CARL -ALPER Hahnemann Medical College, Philadelphia, Pennsylvania
BIOLOGICAL chemistry is a study of the nature of the structural components of tissues and the metabolic changes going on a t all times inside the living cell. In addition to a qualitative description of the structural comoonents of the animal bodv, biochemistw describes
are formed from basic precursors. These reactions are controlled chemically by the amounts of matter and energy involved in the specificbiochemical reaction and physiologically by the nervous system and the hormones of the endocrine glands. Introductory courses-in chemistry emphasize the concept of chemical equilibrium and the nature of TABLE 1 Fundamental Concepts of Chemistry Relating to the chemical reactions (Table 1). These concepts apply throughout the realm of chemical reactions, whether Nature of Biochemical Reactions they are carried out in a reaction chamber such as a test Application to biochemical tube or in a reaction chamber such as a living cell. reaetim The distinction between these two systems is that in (1) Weight relations in Matter and energy are not lost. chemical reactions but may be interconverted. testAube experiments the reaction may be controlled This permits the biochemical easily by the investigator, whereas in the cell the conand camrvation of matter and enerev atoraee of enerev-rich com-. vounas which mafbe utilized as trols are a function of the internal environment, t h e hormones, and the nervous system. needed. (2) Mass action and the Rates of reactions are variable. Courses in organic chemistry describe a vast number speed of chemical reIn addition to external factors, of chemical reactions based upon the chemical nature actions reaction rates depend on the effective concentrations of the re- of certain reactive groups, ring and chain structures acting substances; the concen- (Table 2). Recently efforts have been made successtration of substances in biochemical rreations is in the order fully in the interpretation of organic reactions based upon electronic structures (1-6). of micro amounts. (3) Chemical equilibrium Reaotions may either go to comA systematic study of biochemical reactions is genpletion or to equilibrium. Fre erally lacking in the course in biological chemistry. The reason for this may be that in the past students of biochemistry have placed little emphasis on the interreh i z e d in a second reaction. lationship between chemical structure and the func(4) Catalysis Reactions may be speeded up by specific chemical agents. Pbys- tional and metabolic aspects of biochemistry. Courses iological catalysts are protein in bioloeical chemistrv include discussions of the enzymes; they are very specific chemist6 and metabolism of carbohydrates, fats, and in their activity. (5) Homogeneous versus Biochemicd rreations may be car- proteins, enzyme chemistry, and biological oxidation and reduction. In many of the textbooks emphasis is r i d out in true solutions, a t the dispersed systems interface between fat and an placed upon enzyme nomenclature and classification, aaueous solution. and a t the int e h c e between 'the mitochon- whereas little or no interest is demonstrated in the drial surface and rtn aqueous fundamental types of biochemical reactions that occur. solution. Although much information may be gleaned from a (6) Valence, chemical af- Biochemical compounds are clas- classification of enzymes (Table 3) according to the finity, and molecular sified as organic compounds. structure Some exhibit the .relatively modern point of view, the average student cannot be simple structures of aclds, esters, expected to accomplish this for himself. alcohols, aldehydes, and keThere is no significant difference between reaction tones. Others i r e c6mplex proteins, lipids, polyssceharides, types in biological chemistry and organic chemistry condensed rines. and heterocv- except that in physiological systems, as a rule, the reacclic compound;.' tions are catalyzed by enzymes and carried out under very mild conditions (Table 4). the quantitative composition of the body, that is, the It is the purpose of this review to demonstrate the size of the body compartments: (1) volumes of the relationship of reaction types in biological chemistry fluid compartments; (2) the equivalence and osmolarity with the previous experience of the student in organic of the ionic environments; and (3) the masses of chemistry and to compare the factors which control mineral constituents and cell solids. Metabolic reac- chemical reactions inside the cell with those in the test tions describe the chemical changes whereby substances tube. 282
JUNE, 1954 FACTORS CONTROLLING BIOCHEMICAL REACTIONS
TABLE 3
The fundamental reaction with which all students of chemistry are familiar is the representation of a double replacement or metathesis reaction:
+ mB
rC
(1) Hydrolasea (cleave a reactive group) (a) Ester+s (b) Glvcosidases
(1)
A+B=C+Dienergy nA
C l d c a t i o n of E n z y m e
+ s D 3~energy
(2)
The equation as written represents the relative number of molecules of each substance which participate in and result from the reaction. It also represents the fact that neither matter nor energy is lost in the reaction. However, the equation does not describe the factors which control this reaction and leaves open for consideration the following questions: (1) How is the reaction initiated? (2) Does the reaction go to completion or achieve an equilibrium state? (3) What determines the rate of attainment of equilibrium? (4) What happens to the end products of the reaction? In the purely chemical system (Table 5) the reaction is initiated and controlled by the investigator. In a biochemical system (Table 5) the exact mechanism for the initiation of a cycle of metabolic reactions is not well understood. Finite physiochemical control is manifested by the nervous system, neuro-humoral agents in conjunction with hormones, the concentration of enzymes and coenzymes, and the internal physiological environment (7) made up of electrolytes, nonelectrolytes, and macromolecules. Under the mild conditions of the cellular environment, which are fairly con-
(2)
(d) Peptidases (e) Pbosphaddases Cf) Polyphospbatases (a) C-S hydrolases (h) C-C hydrolases Tramjerases (tranafeming part of the donor molecule except hydrogen or electrons to the acceptor molecule) (a) Transmethvlase (b) Transscetyiase (c) Transglycosidase id1 Transnhosohatase (g)
ransadenylase Transsulfurase
(a) Aerobic and anaerobic transhydrogemses (b) Aerobic and anaerobic transelectronases (c) Peroxidases and catalases (4) Lyases and svntheases ~ n a y m e splitting s or synthesizing C-C bonds (b) Enzymes splitting or synthesizing C-N bonds (c) Enzymes splitting or synthesizing C-S bonds (d) Enzymes splitting off or adding HsO (5) Isomerases and racemes (catalyze molecular rearrangements)
(a)
' HOFFMAN-OSTENHOP, 0.) Advanees in E ~ y m d . ,14, 219 (1953).
stant for all biochemical reactions, the physiological controls of biochemical reactionsserveto agtivate suecific biochemical reactions, to control the pathway of
TABLE 2 Soms Organic Functional Groups Important i n Biochemistry Name
Formula
Class of compound
Biochemical compounds
-
Hydroxyl group
-OH
Alcohols
Carboxyl group
-COOH
Acids
Carbonyl group
>C=O
Aldehydes and ketones
Amino group Sulfhydryl group
-NHI -SH
Amines Mercaptans
Phenyl group Cyclopentanoperhydropbenanthrene
Pyridyl Group
0
Alcohols Carbohydrates Hydroxy acids Acid Carbohydrates Keto acids Glyceraldehyde Amino acids Thio acids Methiol compounds
Aromatic
Amino acids
Polyeyolic condensed ring
Steroid hormones Bile acids Vitamin D
Heterocyclic N compound
Niacin, vitamins Bs and coenzymes
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As soon as a compound is formed in a given transformation it is used up as the substrate in the succeeding reaction. This mechanism does not permit the ac( 1 ) Temperature Reactions proceed at 37'C. (2) Hydrogen ion concen- Approximately neutral, pH 7.34. cumulation or piling up of any one constituent. If in some way a biochemical transformation is partially tration (3) Oxidation-reduction po- Temperate redox potential, rH 17- inhibited or completely blocked, as might occur in tential 22. certain pathological disturbances or because of the ac(4) Concentration of react- Extremely low. ants tion of a drug, then one should expect a building up of (5) Single solvent system All biochemical reactions take the concentration of the final compound formed with place either in dilute aqueous solutions or at the interface of its consequent effect on the equilibrium of the reaction such solutions with fatty, fi- in which it is formed. brous, or mitochondria1 layers. Finally, before leaving this subject it is necessary to (6) Concentration of en- Under physiological conditions this should be fairly constmt. consider the concept of reversihility of biochemical rewme actions. For chemical reactions to he freely reversible there must be no resultant change in the free energy of metabolism of a given substance, and, finally, to inte- the system. Frequently in biochemical systems, where grate the metabolic pathways of a number of physiolog- temperature and concentrations of reactants vary relaical substrates to yield useful energy and precursors tively little, there is a net decrease in free energy; and, therefore, for a reaction to he reversible an input of for tissue synthesis. In addition to the factors which determine the rate energy is required to maintain energy balance. Cona t which a biochemical reaction (Table 4) reaches equilibrium in vitro, one should consider the point of TABLE 6 equilibrium for the entire biochemical system in vivo. Fundamental Types of Biochemical Linkagw (Linkages Between Carbon and Related Atoms) Not only is the rate of the end reaction a function of the .. . . . factors previously discussed, but it is subject to the Amino acids Carbon-Carbon Monomccharides rates of food intake, food digestion, metabolite absorpFatty acids and esters tion, metabolite transport, metabolism, tissue synthesis Alicyclic compounds and breakdown, and excretion. The over-all rate of the Fatty acids and esters Carbon-Oxygen system is a function of the rate of the slowest reaction. Monosaccharides Glyeosidos Thus, the equilihrium constant, which is calculated Alcohols from the respective concentrations of the reactants and Aldehydes Ketones end products of the reaction after equilihrium has been Amino acids Carbon-Nitrogen attained, is in reality a summation effect of all of these Amides factors. It must he realized, however, that in bioPeptide linkages chemical systems the contribution of any one of these Glucosamine Heterocyclic compounds physiological factors to the final result cannot he evalAmino acids Carbon-Sulfur uated. Since the concentrations of reactants in hioHeterocyclic compounds chemical reactions are very low (frequently in the range of micromoles of reactants) only with the recent development of micro and nltramicro analytical tech- sequently, although many hiochemical reactions are reniques have measurements of equilibrium constants of versible, others are not because of the decrease in free energy of the system. Since systems of biochemical biochemical reactions in nitro become possible (8a). Metabolism is a complex system of biochemical re- reactions have a common starting point and must be actions functionally linked together in coupledreactions. able to return to this starting point, we have devised the concept of cycles of metabolic reactions. This concept is essential and has proved to be true. It is the only way in which a starting point may be restored TABLE 5 An Analysis of an In Vim end In Vitro Chemical if one of a system of coupled reactions is irreversible. Transformation We also observe that the chief manifestations of life, (1) Chemical transGlycogen 8 0 n-Glucose synthesis and growth, are irreversible processes. Thus formation I n oitro In vivo we must conclude that the reversibility of individual (2) Initiation of reac- Man-controlled Hormonal hiochemical reactions is not carried over by the comtion HC1 at boiling plete biochemical system. Catalysis TABLE 4 Physiological Environment of Biochemical Reactions
+
-
temp. Net energy change Wasted Final outcome of Reaction goes to reaction completion nmiic equilibrium Fate of end prod- End products End products are u s e ucts accumulate ful in enerev o m duetion or-lormation of glycogen de
FUNDAMENTAL TYPES OF BIOCHEMICAL LINKAGES
Prior to a consideration of the nature of hiochemical reactions, i t is necessary to review the structure of compounds that play an important role in biological chemistry. Generally, inorganic ions are important in the maintenance of osmotic equilibrium. The only in-
JUNE, 1954 organic chemical reaction of importance in biological chemistry is the formation of apatite and apatite-like salts in the formation of bones and teeth. Orzanic chemistrv. which encomvasses the chemistry 2 carbon compounds, was originally so designated because a t that time it pertained only to the chemistry of plant, animal, and micro-organism materials. In the chemistry of living systems the compounds of importance exhibit carbon-carbon, carbon-oxygen, carbonnitrogen, and carbon-sulfur bonds (Table 6). The C-0, C-N, and C-S classes of compounds represent groups which are chemically and physiologically very reactive. We might state this as an axiom to the previous statement: all polar bonds are chemically and physiologically very reactive. The fundamental types of biochemical linkages are peptide, glycoside, and ester in proteins, carbohydrates, and lipids, respectively (Table 7). In addition to these we find demonstrated in biochemical comnounds acid anhydride, acyl, phosphate ester, and pyrophosphate linkages. Thus it is to be noted that biochemical compounds may be classified either as organic compounds or as organic chelate complexes. Generally, the structures of the biochemical macromolecules (naturally occurring high molecular weight polymers) are exceedingly complex and have not been completely determined. For example, although the naturally occurring amino acids are known, i t is difficult to ascertain the succession of amino acids in a protein molecule. The possibilities for such combinations are limitless. By way of contrast, the structure of the synthetic polymers such as nylon, Buna rubber, and rayon are well known. In addition to their complexity of structure, biochemical compounds exhibit a higher degree of lability than the commonly known organic synthetic polymers. This property results in added difficulties in the determination of the structures of the naturally occurring macromolecules.
TABLE 8 Fundamental Types of Biochemical Reactions Lytic reactions (a) Hydrolysis ( b ) Phos~horolysis Transfer reactions (a) Tr.mmethyletion ( b ) Transphosphorylation (c) Tran&ylition~ ( d ) Transglucosidation (e) Transamination if) Transesterification (g) Transpeptidation (h) Transamidination Oxidation-reduction reactions (a) Loss of hydrogen ( b ) Gain of water, loss of hydrogen
~.
(5) Isornerization and raeemization
of carbohydrates, proteins, and fats from animal and plant sources. These substances are converted in the digestive tract by hydrolytic and phosphorolytic reactions into simple compounds (Tables 8 and 9). Following entry into the circulation, these simple compounds TABLE 9 Digestion of Biochemical Fuels original fuels-
Carbohud~ales
Starch Glycogen Sucrose Lactose Pentose Following di- Glucose gestion enter Fructose circulation Galactose as:
FUNDAMENTAL TYPES OF BIOCHEMICAL REACTIONS
The fuels which are ingested to maintain the energy requirements for life and to provide precursors for tissue syntheses are complex structures. The foods consist TABLE 7 Fundamental Types of Biochemical Linkagea (Linkage. Between Simple Molecules) Cornpound
Protein
Carbohydrate Li~id
Organic phosphates
Linkage Peptide Amide Salt Hydrogen bonds Glycoside , Aeetal Ester Acid Acid anhydride Aeyl compounds Ester Acid anhydride
Pmteins
F&
Animal and Fats and vegetable other lipids proteins Low mol. wt. polypep tides,amino &!ids, punne and pyrimidine bases
Glycerol Fatty acids Choline HaPO4 Cholesterol Cholesterol esters
eventually find their way to the sites of metabolic activity in the animal organism. The products which are assembled in the liver and other tissue cells constitute the metabolic pool (Table 10 and the diagram) and will be used for tissue synthesis and energy production, or will be excreted as end products of metabolism. The biochemical reactions observed in the course of metabolism (Table 8) include transfer reactions, oxidation-reduction reactions, condensation reactions, and isomerization and racemieation. Hydrolytic Reactions (9-16)
The principal reaction of the digestive tract is that of hvdrolvsis. The excess of water would favor the state or eankbrium that amroaches complete hydrolysis. A condition that further favors complete hydrolysis of fats, carbohydrates, and proteins in the digestive
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activation of the gronp on which the replacement is to occur. (a) Transmethylation (29-24) is the biological transfer of preformed methyl groups from dietary sources. The naturally occurring methyl donors, that is, the compounds which have a labile methyl gronp, are choline, betaine, dimethylpropiothetin, and methionine. Transmethylation plays an important role in the biosynthesis of methionine, choline, sarcosine, and creatine. The labile methyl gronp of methyl donors also provides the N-methyl group of epinephrine and N'methylnicotinamide.
TABLE 10 Metabolic Pool (Labile Reserve) Carbohudmfm
Glucose Fn~ctose Z-C residue 1-C residue
Fats
Proleins
Proteins Fat Amino acids 2 4 residue Polypeptides Ketone bodies ZC residue l-C residue Urea Other N products 1-C residue
tract is the removal from the site of reaction of the smaller fragments by the absorption of the products of hydrolysis into the circulatory system. The products R-CHI + R'H R'-CHa + RH (9) which are absorbed are transported to the major sites Betaine + Homocysteine Methionine + Dimethylglyoine (lo) of metabolic activity. By way of contraat, organic (b) Transphosphorylation (65-67) is the biological hydrolytic reactions have well defined equilibrium contransfer of phosphate from compound A to compound stants. B. This reaction, more freqnent,ly than other trans(a) Proteolysis (14-1 6 ) .
=
H R+ni--c-nr
8
H
I
A
+ HoH-R-cooH
boon
I'eptide bond
(b) Lipolysis (11-1 3 ) . R-C-OR'
d!
Fat
-
+ Water +
HOH
+ Water
+ H,N-A-R,
T k u e cells (Maintains constancy of cornpoaitian Leuel)
Variable intake
(3)
cI o o H Amino acids
+ R'OH
R-C-OH
8
Acid
LABILE STORE
(4)
+ Alcohol
Blood plasma and extracellular Anid (Maintains and reflecta constancy of cornpodtion)
(c) Lysis of glycoside linkage (9, 10).
Variable output
Diavam of Elastic Adjustmant of Body Labile S t o r a
-
fer reactions, probably will carry with i t a change in the content of free energy. The most important phosphate donor compound is adenosine triphosphate. It may be Phosphorolytic Reactions (17-21) considered as a storage depot for potential chemical Phosphoric acid rather than water is the participant energy. ATP participates in a variety of coupled bioin the cleavage of glycosidic bonds in polysaccharides chemical reactions in which the bond energy is conand nucleosides in animal tissues. verted to useful chemical work. This energy is utilized in chemical synthesis, osmotic work, heat, Glycogen + H 9 0 , Glucose-l-phosphate (6) light, mechanical work, and electrical work.
I
Polysaccharide
Sucrose
Inasine
+ Water
-
+ HsPOI
+ &PO4
I
Monosaccharides
Glucose-l-phosphate
Hypoxanthine
+ Fructose
(7)
+ Ribasel-phosphate (8)
Transfer Reactions
The biochemical transfer of groups from one organic residue to another is catalyzed by a group of enzymes known as transferases. This reaction involves the replacement of one component of a sensitive biochemical linkage by another similar component. Although the transfer of whole groups is not a new concept to students of chemistry, snch reactions are more generally peculiar to biochemical phenomena. Occasionally, snch reactions have been observed in organic chemistry; for example, the Gabriel synthesis of glycine from phthalimide. Such reactions, although thermodynamically feasible, do not occur in the test tube except in the presence of an enzyme. Obviously, the phy~iological catalyst lowers the energy barrier and permits the
0
R-$-OH
AH
0
+ R'H +
I.--OH + RH AH
Rt-
Adenosine triphosphate Glucose Adenosine diphosphrtte
-
+ Glucose-&phosphate
(111
(12)
(c) Transacylation (28-31) is the biological transfer of acyl, essentially acetyl, groups from one compound to another. A necessary requirement for this system is the cofactor, Coenzyme A. The discovery of this cofactor and the biochemical reactions in which it participates have led to significant advances in the metabolism of the two-carbon unit and fatty acids. R-4-R' Acetyl-Co A
+ R"H
R-H
+ R'-C-R" 11
+ H,PO, = Co A + Acetyl-PO,
(13)
(14)
JUNE, 1954
287
- + - -+
II
duction as the gain of electrons. In any single system if a substance is oxidized there must be present a second substance which will be reduced. Thus, the electron acceptor is reduced and the electron donor is oxidized. Acetyl-Co A + Oraloscetate Co A + Citrate (16) Practically all of the energy needed by living organisms Co A CI-compound (17) comes from biological oxidation-reduction mechanisms. Acetyl-Co A + Acetate The oxidative processes of living systems have evolved (d) Transamination (32-34) is the biological transfer the following features: (1) energy is released in small of an amino group from an amino acid to a keto acid. increments, no greater than 12,000 calories per mole, This is one of the important reactions involved both in which can be handled readily by living cells; (2) the the synthesis of amino acids from nonprotein sources metabolic reactions which result in the release of free and in the catabolism of amino acids. It is a reversible energy are coupled with other reactions into functional reaction which has been observed to be a general meta- systems which simultaneously provide and absorb the bolic process for almost all of the amino acids with the free-energy changes. There are three types of oxidaexception of lysine. tive changes observed in physiological systems. (a) Loss ofelectrons. COOH COOH COOH Acetyl-Co A
+ RNHl
Ca A
+Rt-Lo
R-&H-NH?
eR
I
R-N-C-4Hz
li
(15)
+
- t o
+
Fe++ e FeC++
1
fer of the amidine radical from arginine, as a donor substance, to glycine in the production of guanidinoacetic acid. This is an essential step in the biosynthesis of creatine.
+ R'H
I
II
H NH Arginine
+ Glycine
-
-
+ RH
(19)
+ Ornithine
(20)
R'-N-CNH.
I
II
H NH Glycocyamine
-
Electron acceptor
(26)
(b) Loss of hydrogen. (18)
( e ) Transamidinatwn (36, 36) is the biological trans-
R-N-C-NH2
c
CH1
CHI
AHOH
* 0 0 + 2H+ + 2 r -1H
&OOH
acceptor
LOOH
CHICOOH
I
-
Electron acceptor (27)
HOOCCH
A
cH~cooH
+
H h o H
+ 2Hf + 2 r
+
H acceptor:+
Electron acceptor (28)
( c ) Gain of oxygen. H,
-
OI
(f) Transglycosidation (21) is the biological replacement of one component of a glycosidic bond by another radical. This reaction leads to the formation of polysaccharides from simple sugars.
-
H,OS
(29)
Since no one such process would provide for the complete conversion of a six-carbon residue to carbon dioxide and water, and since the energy released would be too great if released all a t once by the cell, oxidation is a R-Glycosyl + R'OH e R'-Glycosyl + R-OH (21) step-wise process. With each oxidative step there is Maltose + Maltotriose Maltotetrose + Glucose (22) liberated a small amount of energy which may be utilized for the immediate physiological requirements of the nsucrose e (Glucose), + nFmctose (23) organism or may be stored for future use. (g) Transesterification (87) is the biological replaceFrequently, biological oxidations proceed according ment of one component of an ester linkage by another to the following pattern: organic group. Such a reaction serves as an important (a) Loss of hydrogen to form a double bond: mechanism for the synthesis of lipids.
=
RCOOR'
+ RUOH
RCOOR"
+ R'OH
(h) Transpeptidation (38,39)is the biological replacement of one component of a peptide bond by another organic radical. This reaction leads to the formation of polypeptides and proteins. H R'
H H
(24)
H
I
R-CH?-CH~COOH
I
e R-b=b- coo^ + ZH++ 2 . (30)
( b ) Addition of water to form an hydroxy acid: H H R-&A-COOH
H
H
I + HOH e R-C-C-COOR I
AH k
(31)
(c) LOSSof hydrogen to form a keto acid: H
H
Rd-&-COOH
AH k
Oxidation-Reduction Reactiom (86, 40)
Oxidation is defined as the loss of electrons and re-
H 5 R-C-&-COOH
+ 2H+ + 2 ~ ( 3 2 )
oI1 HI
(d) Oxidative rupture of the carbon chain to form an acid with two carbon atoms less; or in some instances where an alpha keto acid has been formed, oxidative
288
JOURNAL OF CHEMICAL EDUCATION
decarboxylation to form an acid with one carbon less in the chain. H
= R-cooH + c H z c o o H
R-cAcooH
4 IL
R-C-COOH
tl
+ '/noz= R-COOH + COz
(33) (34)
Condensation Reactions
-
These reactions are not well understood in biolo~ical chemistry. Although we may consider all of the transfer reactions as forms of condensation reactions, this section is concerned mainly with the addition of C1and Cz- fragments to pre-existing organic residues. These reactions are important in the synthesis of larger biochemical comwounds from the small oreanic wrecursors found in the metabolic pool. (a) Aldol Condensation (&). ~
~
~~~~
Iaomerization and Racemization (47)
There are several molecular rearrangements which are well established in biological chemistry. These rearrangements occur a t several different points in the metabolic cycle. They are generally not energy-yielding reactions, but serve to prepare substrates for other reactions which provide energy or special precursors for tissue synthesis. (a) Transformations of structural isomers. (1) Aldose-ketose transformation (Keto-en01 tautomerism). (a) Glucose-6-PO, e Fructose-&PO4
( b ) Glyceraldehyde-&PO, (c) Ribose-5-PO,
= Ribulose-5-PO,
01 8
+ C02
HOOC4-CHI-CH-COOH
HOOC-CH2-C-COOH
I1
+ Cone
4
(42)
e 3-PO4-glycerate
(43) (44)
(3) Interconversion of stereoisomers. These reactions result in the exchange in position of reactive groups. (a) Gluoose-1-PO4 d Galactose-l-PO,
(45)
(b) Citrate e Isocitrate
(46)
(37)
(b) Racemization is the process whereby half of an optically active compound is converted into the enantiomorph with the resultant formation of the dlmodification. Although this is the commonly accepted term for the biochemical reaction to be described, it is a misnomer. This reaction, which is in reality an optical inversion, was mislabeled because the enzyme had been named a wcemase.
(38)
(1) d-lactic acid F? I-lactic acid
(47)
(2) d-allanine
(48)
0
HOOC-C-CH-CH9-COOH
tone-PO,
= GlucaseG-PO,
(b) >PO,-glycerate
CHI
