CHLOROPHYLL and HEMOGLOBINT W O NATURAL PYRROLE PIGMENTS EMMA M. DIETZ* Harvard University, Cambridge, Massachusetts
C
HLOROPHYLL is the brilliant green pigment found in certain special cells of all green plants. I t absorbs energy from the sun and in some unknown way uses it for the manufacture of sugar, starch, and proteins (1). This important process is known as photosynthesis and ultimately provides food for all plants and animals on the earth. Hemoglobin is the red pigment coloring the red blood cells of animals. It is necessary for the maintenance of l i e through respiration-the process which provides a constant supply of oxygen to the tissues. In the slow development of the chemistry of these two pigments, it has been an increasing source of wonder to chemists to find that two substances of such widely different origin and function are yet so remarkably similar in structure. The pure pigments as isolated in the laboratory are very different in appearance. Chlorophyll, when separated from the leaf structure, is a dark green wax which is really not one substance but two closely related ones, called chlorophyll a and b by Willstatter. Hemoglobin is a compound molecule consisting of a colorless protein (globin) attached to four molecules of a red-brown crystalline pigment called heme. In the process of isolation from hemoglobin, heme changes over to its familiar oxidation product, bemin, which is a brownred crystalline compound of high melting point. When chlorophyll is dissolved in ether or chloroform a brilliant green solution results; hemin forms a red-brown solution. When observed through a spectroscope, solutions of either pigment show the remvkable property, due to similar elements of structure, of absorbing sharp bands of visible light. There results an unusual banded spectrum in the visible region, which is characteristic for each compound and serves as a valuable means of identification. An important diierence between the two pigments which is immediately apparent from a chemical analysis, is that chlorophyll contains magnesium, whereas hemin contains iron incorporated in the large organic molecule. The widespread distribution and importance to life of both substances early stimulated the interest of sdeutists. The chemistry of chlorophyll was confused for some time by the use of drastic methods of isolation which altered or destroyed the molecule and introduced metallic impurities. I t is still a matter of concern to the chemist to find means of isolating this complex
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* Sarah Berliner Fellow. American Association of University Women, 1934-1935, at present engaged in research at the University of Munich, Munich, Germany.
material without introducing subtle changes in structure. Heme, the pigment now believed to be present in hemoglobin, was long mistaken for its close relative hemin, to which it is readily converted during isolation. There are many similar instances in the history of the chemistry of natural products where faulty isolation bas obscured the true structure for years. RELATIONSHIP
BETWEEN
CHLOROPHYLL AND
HEMIN
The first suggestion of a relationship between hemin and chlorophyll was made as early as 1851 by Verdeil (Z),though on the basis of invalid evidence. He unwittingly introduced iron into his preparations of chlorophyll by employing crude methods and reagents, and as a result thought that it might be related t o hemin, which was already known to contain iron. Actually, the similarity in the two pigments is not in the metallic constituents but in the rest of the molecule. However, Verdeil's hypothesis stimulated research on the problem for years and culminated in the series of brilliant investigations by Hans Fischer for which he was awarded the Nobel Prize .in 1930 (3). He and his co-workers fmally established the correct structure of natural hemin and heme by synthesis, and showed their true relationship to chlorophyll. Research on the plant pigment benefited enormously by these results, but its structure is not yet absolutely clear and its complete synthesis has not been accomplished. In the present discussion of the subject it has been found convenient to follow the historical development, and t o consider 6rst the structure of hemin and its relationship to chlorophyll, before presenting the detailed structure of the latter. The 6rst real evidence of the connection between chlorophyll and hemin was theformation of very similar red,.crystalline compounds called porphyrins, from both blood and plant pigments. These were first obtained by Hoppe-Seyler (4) in 1879, later by Schunck and Marchlewski (5) by drastic chemical treatment of the two pigments. These porphyrins formed bright red solutions in ether with striking four-banded absorption spectra in the visible region, and they were actually close chemical relatives though not identical as a t first supposed. In 1901, Nencki (6) reduced both hemin and a crude preparation of chlorophyll to mixtures of volatile bases called pyrroles (seeI),thus showing for the f i s t time that pyrrole nuclei were involved in the structure of both pigments. Willstatter (7) later identified the same
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H
Methyl Ethyl Maleie Imlde
pyrrole fragments from both chlorophyll and hemoglobin, thus proving a very close relationship. Kiister (8) studied the products of drastic oxidation (11) as well as reduction and proposed in 1910 the correct general formula for the nucleus common to the porphyrin, hemin, and chlorophyll molecules. It was not until twenty years later, however, that the Kiister formula was completely justified by the synthetic results of Fischer. THE FORMULA OF HEMIN
X = Fe++) the iron is in the reduced form, without the halogen atom. The interconversion between protoporphyrin and its two iron derivatives is readily accomplished in the laboratory. On drastic reduction of hemin and heme the metal drops out and the porphin ring breaks on either side of the bridge carbon atoms, forming the pyrroles shown in I ; oxidation removes the bridge carbon atoms completely, forming hematinic acid (see 11) as stated above. I t might be mentioned here that hemin and heme are class names applied to Feel++ and Fe++ complexes of all porphyrins, but have been adopted as the specific names for the blood pigment derivatives, more correctly called protohemin and protoheme. Further, the use of non-systematic names, wherever possible in this field, is preferable to the very lengthy Geneva nomenclature, though somewhat confusing at first. These incidental names are usually derived from Greek stems denoting color, i. e., chlorophyll = green leaf, porphyrin = purple.
A detailed examination of the hemin formula will bring out several features, shared by chlorophyll as well. It contains four pyrrole, or modifiedpyrrole nuclei bound into a large symmetrical ring structure by four carbon atoms. For purposes of nomenclature, the unsubstituted molecule is called a porphin ring. In hemin there is an unbroken alternation of single and double bonds such as is assumed for all porphyrins, and is found on a smaller scale in benzene. As in benzene, the exact location of each bond is not determined and various arrangements are possible. The evidence BLOOD AND CELOROPHY2.L WRPHYFSNS of years indicates that most compounds exist in only The correctness of these, structures for protoporone of the possible electromeric forms, and it remains phyrin and its iron derivatives was proved through for physico-chemical methods, such as electrometric the isolation and identification of their degradation titration [as applied by Conant to some chlorophyll products and finally through the synthesis of the whole derivatives ( 9 ) ] to determine which form is present.
:.
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Heme = Protoheme Hcmin Protohemin
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X Fe++ X = l'eCltt
Only one possible electromeric structure of each compound is shown here for convenience. In hemin (Formula 111; X = FeCl++) two hydrogen atoms of the parent porphyrin, protoporphyrin (Formula IV; X = -CH=CHe), have been replaced by an FeCl++ grouping which is doubtless coordinately bound to all four nitrogen atoms. In heme (Formula 111:
series of blood porphyrins by Fischer. In protoporphyrin, as in hemin, there arefourmethylgroups (-C-CHnCOOH >C=CHCOOH >CHCHOHCOOH
Fischer, X =
Conant, X
=
place in the presence of acid and alkali. All of these qualifications are fulfilled by chlorophyll or the pheophorbides, which contain the same grouping. Thus Stoll prepared a benzoyl derivative of methyl phipophorbide a (30), showing the presence of an hydroxyl group. Later Fischer discovered the conditions necessary for oxime formation (31) after fruitless attempts by several investigators. This evidence indicates that the fifth oxygen atom can function as part of either an hydroxyl or a carbonyl group. The starting material was recovered unchanged from both derivatives by hydrolysis. I t was this evidence for a carbonyl group which, in 1934, seemed to rule out the Conant and Stoll formulas, since neither as such contains a group capable of forming an oxime. Alkali hydrolyzes the ester groups and splits the carbocyclic ring of chlorophyll forming the tribasic acid chlorin c (Formula XIII). Strong acid retains the ring structure, although hydrolyzing the ester groups and removing carbon dioxide from the free bridge carboxyl group, forming phylloerytbrin (Formula XIV). These reactions of chlorophyll in acid and alkali are also characteristic of beta-keto esters and therefore support the Fischer formula. Pbylloerythrin was first isolated by Marchlewski (32) and has since been found frequently as a degradation product of chlorophyll in the animal body (33). Fischer early suspected a close relationship between the two, and after proving that phylloerythrii contains a carbocyclic ring was led to postulate a similar ring in chlorophyll. The structure of phylloerythrin was thoroughly established by the synthesis from methenes of its reduction product, desoxyphylloerythrin (34),and by its alkaline degradation to phyllo-, pyrro-, and rhodoporphyrins. The same carbon ring is also de6nitely present in pheoporphyrin as (35), a porpbyrin isomeric with ph~ophorbidea and produced by very mild hydrogen iodide treatment of chlorophyll or phipophorbide.
I t will be noted that there is an ethylidene grouping (=CHCH8) in Fischer's formula for chlorophyll a which does not appear in any of the others. This was recently postulated as the result of newly discovered evidence and is thought to be present in all derivatives of chlorophyll except porphyrins, which have an ethyl gronp in its place. This newly detected group appears to take up two atoms of hydrogen, and with hydriodic acid to be oxidized to an acetyl group, which can be split off, leaving a free hydrogen atom. Two compounds resulting from such degradation reactions have been synthesized and the position of this group may be regarded as established although its exact nature is not quite so certain. One very important reaction of chlorophyll which also centers in the disputed carbocyclic ring is called allomerization and was discovered by Willstatter and Utzinger (36). This is a subtle change takimg place in alcohol solution, whereby the abiity of the pigment to show a certain Molisch color reaction is lost, but no change in color or spectrum is observed. Conant made the valuable discovery that allomerization is a dehydrogenation reaction (37) involving two chemical equivalents, in which either oxygen or potassium molybdicyanide can serve as agents. He also found that allomerized chlorophyll ditrers in behavior on alkali treatment from the unallomerized material. Thus he demonstrated the formation of a ketonic add (-COCOOH), pheopurpurin 7, from allomerized chlorophyll (38), while unaltered chlorophyll yields an hydroxy acid (-CHOHCOOH), chlorin e hydrate, which dehydrates on isolation (39). Conant therefore postulated an easily formed hydrate of chlorophyll (see Formula XII), with a secondary alcohol gronp capable of being dehydrogenated to a carbonyl group, as the seat of allomerization. The proof of a similar dehydrogenation of a --CHOH group in chlorin e hydrate seemed to lend weight to this hypothesis. Stoll later incorporated Conant's interpretation of allomerization into his formula, but dropped the idea when Fischer demonstrated the presence of a carb8nyl group in unaltered chlorophyll. Fischer, on the basis of allomerization experiments assumes that the dehydrowith qninone in alcohol (M), genation takes place between the gamma and 10 positions, forming a double bond, and that the molecule may then add water or alcohol to the carbon atoms at positions 6 and 10 (1,4addition) as is shown below.
XV.
Thus according to Conant the addition of water must precede dehydrogenation, while according to Fischer water cannot add until dehydrogenation has taken place. Careful analysis of purer samples of allomerized products and a further study of the properties of Fischer's 10-hydroxy methyl ph~ophorbidea might help to clear up this difficulty. This compound on Conant's formulation would be a hydrate of the unallomerized material. Against this view is the fact that the compound is always prepared in allomerizing media, and also that it no longer forms chlorin e on alkali treatment, a criterion for unallomerized material. Conant and Fischer have postulated d i e r e n t chlorin e formulas consistent with the formation of chlorin e with alkali, or its ester with diazomethane, from their respective structures for ph~ophorbidea. The behavior of chlorin e hydrate as au alpha-hydroxy acid in the presence of suitable oxidizing agents h d s no explanation in Fischer's formula, which is satnrated and cannot form a hydrate. This casts some doubt not only on his formula for chlorin e but also for phaeophorbide from which it is derived. Aside from the determination of the nature and location of substituent groups on the chlorophyll skeleton, there remain problems in connection with the h e structure of the nucleus which will doubtless require new methods of attack. Conant and Kamerlimg compared the absorption spectra of chlorins and porphyrins a t liquid air temperatures (41), and found the difference similar to that between benzene and dihydrobenzene under the same conditions. They suggested, therefore, that there is a completely conjugated system of double bonds in the porphyrins which-is broken in the chlorins by partial hydrogenation. Cofiant has shown further that chlorophyll can be converted into a simply constituted chlorin, chlorin f, by transformations which do not affect the nucleus; and that chlorin f is a dihydro derivative of a porphyrin, isorhodoporphyrin (4Z), an isomer of rhodoporphyrin (43). This evidence indicates that chlorophyll has the nucleus of a chlorin (or dihydro-porphyrin). Fischer accepts the assignment of additional hydrogen atoms to the inner porphin ring of the chlorins and chlorophyll but, since he postulates a free ethylidene group on one pyrrole ring, the total hydrogen content of both chlorins and porphyrins is kept the same. This assumption is based on catalytic hydrogenation data indicating that they are isomeric (44). Thus conflicting chemical evidence has
Frscmds INTERPRETATION OF ALLOMERIZATION
led to a diierence of opinion as to the state of oxidation tailed structures of chlorophyll and of hemin from the of the chlorophyll nucleus. Conant believes the chloro- point of view of their interconversion in the animal phyll skeleton to be that of a dihydro-porphyrin, body. As explained above, chlorophyll has either a dihydro- or an iso-porphyrin ring rather than a porFischer thinks it is that of an isomerized porphyrin. A further application of physico-chemical methods phyrin ring, and its substituent groups correspond more to the determination of nuclear structure is the electro- closely to mesoporphyrin than they do to hemin. metric titration by Conant of the individual basic Therefore, no simple theoretical transformation can pyrrole groups in various chlorophyll derivatives in be postulated. This, however, does not exclude the biological possibility, although the degradation prodglacial acetic acid solution (9). ucts of chlorophyll thus far found in the human and animal body are not suggestive of a direct transformaCHLOROPHYLL B tion. Nevertheless, many investigators have claimed Chlorophyll b, as Willstiitter's analytical results to 6nd a positive reaction of chlorophyll in anemia preshowed, d8ers from the a component by only one oxy- vention and therapy in animals. The common type gen atom. Conant (45) [and later also Warburg of pernicious anemia is believed to be due not to lack (&)I obtained carbonyl derivatives of compounds of of red pigment but to other factors necessary for the the b series and so placed this oxygen atom in a carbonyl origination of red blood cells in the bone marrow. group (capable of enolization) on one of the bridge Hence chlorophyll feeding might not be expected to carbon atoms of his structure for chlorophyll a. He help. Perhaps a more significant experiment is that assigned it to a position on the nucleus in order to ac- of Patek and Mmot (51) who investigated human pacount for its enormous effect on the absorption spec- tients with a rarer type of anemia caused by pigment trum. Fischer fist placed this group in the beta posi- scarcity and observed a small positive increase in tion of the propionic acid residue (47), but has recently hemoglobin concentration on intravenous injection of moved it to a formyl group in position 3 of pyrrole ring a chlorophyll derivative (chlorin e). The very small I1 in his formula for chlorophyll a (48). effect makes it probable that under the conditions of Besides the carbonyl group characteristic of this the experiment, chlorophyll and its derivatives merely series, chlorophyll b seems to contain the same carbo- break into simple pyrrole fragments in the body which cyclic ring as the a compound. Thus Stoll isolated a are then available for recombination to hemiu, but dioxime of methyl phaeophorbide b (49) and Fischer that the conversion is not very e5cient. The tetrapyrryl ring structure not only plays an has prepared a number of porphyrins paralleling the phm- and chloroporphyrins of the a series (50). The important r61e in the photosynthesis of plants and in greater scarcity of chlorophyll b and the greater diffi- the respiration of animals, but has recently been deculty of purification of its derivatives have delayed tected in such powerful body.,catalysts as catalase progress in this series and its formula is less certain (52) and peroxidase (53) and in the cytochrome c of than that of the a derivative. There is no evidence of yeast (54). Traces of porphyrins are found very widethe interconversion of the two series in the plant nor spread in nature but usually without any obvious biois there any explanation of their very constant ratio logical function. Future research will undoubtedly as observed by Willstitter. uncover further examples of the intervention of this We are now in a better positiqn to compare the de- type of molecule in important natural processes. C
LITERATURE CITED
(1) Recent developments on the nature of photosynthesis and the rdle played by chlorophyll are summarized in a review by H. A. Spoehr: "The chemical aspects of photosyn-
thesis," Stanford University Annual R&m of B w c h istry. 2, 453 (1933). (2) V E ~ ECompt. ~ , rend.. 33, 689 (1851). (3). FISCHER. Nobelvortrag Stockholm 1931; Z. onam. . Chic,
.
44, 617 (1931). ,, (4) HOPPE-SEYLER, "Uber das Chlorophyll der Hamen," 2. physiol. Cham.. 3, 339 (1879); 4, 193 (1880). PIOC.Roy. Soc., 50, 302 (1891); SCRUNCK urn (5) SWIUNCK, MARGUEWSKI, inid., 57, 314 (1895); "Zur Chemie des Chlorophylls," Ann.. 284, 81 (1894). "Uber die Reduktionsprodukte des (6) NENW urn ZALESKI,
Himins und iiber die Konstitution des Hiimins und seiner Derivate," Bcr.. 34, 997 (1901). (7) WILLSTKTTER UND ASCHINA."0nydatian.der Chlorophyll Derivate," Ann., 373, 227 (1910); "Uber die Reduktion des Chlorophylls. I." ibid., 385, 188 (1911). (8) Kiismn, "Beitrige zur Kenntnis des Bilirubins und Hiimins," 2.ghysiol. Cham., 82, 463 (1912). (9) CONANT, CHOW. AND DIETZ,"Chlorophyll series XIV. Potentiometric titration in acetic acid solution of the basic groups in chlorophyll derivatives," J. Am. C h . Soc., 56, 2185 (1934).
(10)
WXLLSTATTER IJND F ~ s c m n ,"Die Stammsubstanzen der
Phylline und Porphyrine," Ann., 400, 182 (1913). UND STANGLER, "Synthese des Mesoporphyrins, Mesoh5,mins. und iiber d ~ eKonstitution de Himins," ibid., 459, 53 (1927). ,, (12) FISCHERurn TREIBS, YJh=2 ~tioparphyrine aus Blattund Blutfarbstoffporphyrine," ibid.. 466, 188 (1928). HERD, VND SWIORYOLLER, "Synthesen der Chloro(133) FISCHER. phyllporphyrine Rhodo- und Pyrroporphyrm, s o ~ l edes I'vrro~trooomhvrin5."rbid 480. 109 (1930)
(11) Flscnsn
.
. .
und Deuteroporphyrjns," ibid., 466,178 (1928). (15) FIscHER UND RIEDL,"Uberfiihrung von Chlorophyll-pyrroporphyrin in Mesaporphyrin aus Himin," inid., 486, 179 "Y
,,'ZY.,. loll,
(16) FwcnEn urn E B E R ~ G E F ~"iiber E R , Mesorhodin und seinen Cbergang m Chloraphyll-parphyrinen. sowic Oxydation dss Phylloerythrinr." ibid.. 509, 19 (19334). (17), WILLSTAI-TUR USD STOLL. "Unwr~uchunzen"ber Chloro-
.
phyll." Julius springer, Berlin, 1913; Translated by Scherzand Mertz. Science Publishing Co., 1928. Theoriginal papers occur in issues of the Annolen from 1906 to 1914. F. G., "Die Konstitution des Phytols," Ann., 464, (18) FISCHER, 69 (1928); FISIXER,F. G. IJND L~WENBERG, "Die Synthese des Phytols." ibid.. 475, 183 (1929).
(19) "Fraktionieruna und Reindar- (36) WILLSTATTER WD UrzrNGen, "ober die ersten Umwand. . WINTERSTEINurn STEIN. stellung organischer Snbstanzen nach dim Prinzip der . . lungen des Chlarophylls," Ann., 382, 129 (1911). chromatographischen Adsorptionsaualyse. (a) 11. Mit- (37) CONANT,KAKERLINO,AND STEELE,"The allomeriration teilung: Chlorophyll." Z. physiol: Chem., 220, 263 (1933); of chlorophyll," J. Am. Chem. Soc., 53, 3171 (1931); (6)WINTERSTEIN UND SCHON, zlnd., 230,139 (1934). also reference (27); STEELE. "Chlor~phyll series VI. (20) STOLLAND WIEDEMANN. "Die optische Aktivitat des ChloroThemechanism of the phase test," i M . , 53, 3171 (1931). phylls," Helu. Chim. Ada, 16, 307 (1933). (38) CONANT,HYDE,MOYER,AND DIETZ, "Chlorophyll series. (21) CONANTAND DIETZ, "Chlorophyll studies. XI. The IV." ibid.. 53, 359 (1931); DIETZAND ROSS, "Chloroposition of the methoxyl group," J. Am. C h . Soc., 55, phyll series. XII. The phgopurpurins," ibid., 56, 159, PO0 / 1 ( 1 1 1 > 110?d> -"" \*""",. I ZSCHIELE,"An improved method of purification of chlorolhlorophyll series. X. The phyll a and b, quantitative measurement of their absorption spectra; prwf for the presence of a third chlorophyll component." Bot. Gas.. 95, 529 (1934). FLSCIIER first published a carbucycli~'ring srructurc for chlorophyll in 1931. "Zur Srrul;rur d r i Chloroplrsll 0," Derivate." Ann., 495 (1532). Ann.. 486. 130 (1931). The revised formula shown is 141) ll VII. Evi. . CONANTAND KAMERLING," C h l o r ~ ~ h v series ~ u h l k h e din AS;.. 513, 107 (1934). "Neue Erkenntnisse dence as to structure from mea&&ment of absorption in dder Feinstruktni des Chlordphylii a." spectrum," J. Am. Chem. Soc., 53,3522(1931). STOLLUND WIEDEMANN. "Der Reaktionwerlauf der Phasen- (42) CONANTAND BAILEY, "ChlorophyU series. IX. Transprobe und die Konstitutiane von Chlorophyll a und b," formations establishing the nature of the nucleus," Natum'ssrmschaffen,20, 706 (1933). ibid.. 55, 795 (1933). FISCHER,"Uher Chlorophyll a," Ann., 502, 175 (1933); Pedler Lecture, J. Chem. Soc.. February, 1933. See also (43) DIETZAND WERNER,"Chlorophyll series. XIII. Nuclear isomerism of the porphyrins," ibid.. 56, 2180 (1934). TREIBS, Z. UngW. Chem., 47,294 (1934). STOLLUND WIEDEMANN,"Die Zusammensetzung des (44) F ~ s c m nWNn LAKATOS,"Katalytische Hydrierung in der Chlorophyll Reihe," Ann., 506, 123 (1933); FISCAER, Chlorophylls," Helv. Chim. Acta, 16, 183 (1933). LAKATOS, UND SCHNELL, ibid., 509, 201 (iQ34); FISHER ARMSTRONG, "The const~tutionof chlorophyll," Ckrmistry DND SPIELBEROER. "Teilsynthese von Athyl Chloro&Industry, 52, 809 (1932). phyllide b, sowie iiber 10-Athoxy Methyl Phzophorbide STOLL UND WIEDEMANN, "Uber Chlorophyll a, seine phaseb." ibid.. 515, 130 (1935). positiven Derivate nnd seine Allomerisation," Helv. Chim. Acfa, 16, 739 (1933); also reference (24) above. (45) CONANT,DIBTZ,AND WERNER,''Chlorophyll studies. VIII. ''Chlorophyll CONANT,DIETZ, BAILEY. AND KAMERLING, The structure of chlorophyll b," J. Am. C h . Soc., 53, series V. The structure of chlarophyU a," J. Am. Chem. 4436 (1931). Soc.. 53. 2384 (19311. (46) W n a u n o , "lfber Phmphytin b," Biochmn. Z.. 235, 240, STOLLUND WIEUEMANN, "Die Benzoylverbindungen und 244, 9 (1932). (1931); *bid., Oxime Ton Methyl Pheophorhide a;' Helo. Chim. Acte. (47) FISCHER,BROICH,BUEITNER.DND NUSSLER, her Chloro17, 163 (1934). phyll b (I)," Ann. 498,228 (1932); FISCHER,B m I m n . FISFEER, RIEDMAIR, UND HASENKAMP, "Uber OxyporphyUND NUSSLER, %her Chlorophyll b (11), HENDSCHEL, ixd., 503, 1 (1933). nne. Ein Beitrag zur Kenntnis der Feinstruktnr van Chlorophyll a," Ann., 508,224 (1934). (48) FISCHERUND BREITNER, "lfber Chlorophyll 4" ibid., 511, MARCHLEWSKI. Z. physiol. Chem., 42, 464 (1904); her 183 (1934): ibid., 516,61 (1935). den Ursprung des Cholehamitins." i M . , 45, 466 (1905); (49) STOLL UND WIEDEMANN,"Die Oxime der Phaophorbide "Chemie der Chloro~hvll." Braunschweie. Viewea. 1909. b." HA.Chim. Ada, 17,456 (1934). (50) h s c n s n , HENDSCAEL, UND:NOSSLER, "Nachweis des isacyclisches Ring in Chlorophyll b," Ann., 506,83 (1933). (51) PATEKAND MINOT, "Bile pigment and hemoglobin regeneration. The effect of bile pigment in cases of chronic ~ls&IEn UND H E S ~"Vorkommen von ~h
