COMMUNICATIONS TO THE EDITOR
6196
Vol. 82
TABLE I the relation between these quantities, given by the SOLUBLE D N P AND M g t t ATPASE equation ACTIVITY AHtr Conditions: 23 pmoles Tris, pH 8.5 and 9.0 in presence AR - TmAS - ~ ( T t -r T,) D N P and Mgt+, respectively; 6 pmoles ATP; 0.3-0.75 ER~ECT OBS FAD
ON
+
3
mg. of protein, in volume 0.50 nil. Incubated 10 m i x and 4 min. in presence of D N P and Mg++, respectively, a t 28'. ~- . Extract FAD:
---Millipmoles Pi liberated/mg. protein-1 X 10-1 D N P i -G X 10-'M hTg++-0.00015 0.0045 0.00045 0.0045 M A i 4 ill M
.* .
...
L-6 193 L-7 L-11 L-10 190 L-10' 138 ' Preparation aged
221
213
375 243 48 hours a t
495
605
616
456
475 520
514
421 535 423
508
6i6 4i6
- 17'.
With an aged extract FAD is still stimulatory, but it is incapable of restoring the original level of activity. However, part of the activity loss may be attributed to the existence of a multiplicity of ATPase entities in these extracts,8 only one of which involves a system employing a flavin moiety, but all of which involve Mg++. As with mitochondria and particulate preparations, the soluble ATPase is strongly inhibited by flavin antagonists such as atebrin and chloropromazine. However, the effects of such materials on the ATPase of these preparations differ in several respects from those observed with the particulate preparations3: (1) ATPase activity is inhibited in the presence of D N P or Mg++, there being no evidence of a stimulatory concentration range in the presence of D N P 3a (2) Amytal does not reverse the effect of atebrin, but rather augments it. These results provide the first direct evidence for the possible involvement of a flavin (FAD) in ATPase activity. They differ from results obtained on a soluble Mg+f-ATPase derived froin sonicated m i t o ~ h o n d r i a . ~It must be presumed that desiccation yields a more complex molecule or system which employs FAD as a possible cofactor or prosthetic group. Work is being continued to further detail the function of FAD in ATPase activity.
Here AI7 and AS are the relative partial molar heat and entropy, respectively, of cesium chloride in the solid solution saturated with cesium chloride a t the temperature T,. Tt, is the transition temperature of pure cesium chloride and Ac, is the difference in specific heat of high and low cesium chloride. The above expression simply amounts to equating the free energy of pure low cesium chloride a t the temperature T , with the partial free energy of cesium chloride in the saturated solid solution a t T,. Pure high cesium chloride supercooled to T, is taken as the standard reference state. The equation only requires that the observed condition of no solid solubility of rubidium chloride in low cesiuni chlorideZ prevails up to Tt,. (For further details, the completely analogous treatment of a liquidus curve might be consulted. 4, In the earlier paper,' these approxiniations were iritroduced in equation 1 AI7 = 0
AS
=
-R
111
(2) (3) (1)
p
Acp = 0
Here p is the mole fraction of cesium chloride in the solid solution and R is the gas constant. I t is not obvious, however, that these approximations are permissible. In view of the apparent discrepancy of the transition point depression curve with the heat of transition it woulcj be of interest to obtain numerical values for A I f , A S and Ac,,. A theory by Wasastjerna6 (with modifications by Hovifi)€or the integral heat 01mixing of solid alkali halides may be -used to derive fairly reliable C Y pressions for A H and AS. Starting with Hovi's equations6 and the definition of partial molar quantities, these equations have been deduced
(8) R Penniall, Biochcm. Biophys A d o , in press. (9) R. E. Beyer, i b i d . . 41, 552 (19GO). (10) Fellow of the American Hcart Association.
DEPARTMENT OF BIOCHEMISTRY SCHOOL OP MEDICINE RALPHI ' E X N I A L L ~ ~ UKIVERSITY OF NORTH CAROLINA A3 CHAPELHILL, N. C. RECEIVED OCTOBER 19, 1960
-R
c
111
{ p - (1 (1 1 - 211
)u]
- j>(l-
- 2 P ) ( l --
- en)(l
j)(l
P)li
4-U P -
+ u ) p ( l - p )]
(6)
A previous note' indicated that the observed transition point depression of cesium chloride by rubidium chloride2 cannot be reconciled with the recently observed heat of transition, A H t , , of cesium chloride.a This warrants a closer examination of
In these equations X is the Avogadro nuinbcr, C is the Madelung constant, e the charge of an electron, R the equilibrium distance between cesium and chlorine nearest neighbors in the lattice aad AI< the difference between R and a corresporiding quantity for the rubidium chloride lattice. The three quantities u, ?a and S are given by the equation@
(1) J. Krogh-Moe, J . A m . Chcm. Soc., 8 2 , 2399 (1960). (2) L. J. Wood, C. Sweeney and hl. T. Derbes, i b i d . , 81, 0148 (1959). (3) C. E. Kaylor, G. E. Walden and D. F. Smith, J . Pkys. C k c n . , 64, 276 (1960).
(4) C. Wagner, "Thermodynamics of Alloys," Addison-Wesley Press, Cambridge, hlass., 19.52. ( 5 ) J. A. Wasastjerna, SOC. Sci. I.cnn. Comm. Pliys.-Math , X V . No 3 (1949). (6) V. Hovi, Ibrd., XV, No. 12 (1950).
TRANSITION POINT DEPRESSION OF CESIUM CHLORIDE BY RUBIDIUM CHLORIDE
Sir :
Dec. 5, 1960
COMMUNICATIONS TO THE EDITOR
6197
is soluble in low cesium chloride a t any temperature) the experimental results appear to be inconsistent. SVENSKA SILIKATFORSKNINGSINSTITUTET G ~ T E B O RSWEDEN G, J. KROCII-hiOE RECEIVED SEPTEMBER 19, 1960
THE n
8 can be calculated if the comDressibilitv coefficient,
‘(”) ?p
and the cubic expansion- coeflicient,
-* T *
TRANSITION IN NUCLEIC ACIDS AND POLYNUCLEOTIDES
Sir:
The 2600 A. absorption band of the nucleic acids is often tacitly assumed to be a single electroiiic (E), is known. Equations 5 and 6 have been band. However, spectroscopic studies suggest V dT simplified by assuming that the 6 value for cesium that the seemingly simple near-uItraviolet band is chloride is equal to the value for rubidium chloride. actually rather complex, aside froni the superposiThis is not likely to introduce a serious error, since tion of pyrimidine and purine bands. First i t is the values calculated for some other alkali halides clear’ that the purine absorption band consists of two independent and mutually perpendicularly indicate little variation in 8.: Numerical values for 4€1 and T4.9 have been polarized F P * transitions, involving the conjugaevaluated from equations 5-9, taking for 6 the tion electrons of both rings. Secondly, both in the value 9.1 given by Hovi for rubidium chloride,’ pyrimidines2 and purines2-* there is an n+ir* and calculating R and A R a t various temperatures transition region on the long wave length side of for the unit cell edge interpolation formula given the strong near ultraviolet v i r * absorption band, by Wood, Sweeney and Derbes2 Results are even in aqueous solution. The n+r* absorption given in cal./mole in the table, columns 3 and 4, appears in the N-heterocyclic bases in aqueous for a solid solution of p mole of cesium chloride solution often as merely a shoulder or poorly rewith 1-p mole % rubidium chloride a t the tem- solved inflection in the absorption curve. The n+n* transitions originate in the promotion perature of initial transition. Column 5 gives the of a non-bonding (n-orbital) lone-pair electron on a simpler expression RT In p. hetero-atom (0 or N) to an empty n-antibonding TABLE I molecular orbital. The n+r* transitions are distinguished from w n * transitions by several T A ~ R T I U ~ P A3 T,, OK. inherent characteristics, of which two are of special 0 0 0 735 1.00 interest here: (a) the n+n* absorption bands are of 0.95 4 i3 711 73 intrinsically low intensity, being a t most one-tenth 0 90 14 14 1 139 688 as intense as the ~ i rbands; * (b) the n+n* bands 628 0 80 54 282 278 have transition moments polarized out-of-plane, 0.50 251 652 488 672 whereas the T+T* transition moments are polaThese data show clearly that the approximations rized in-plane for all pyrimidines and purines. represented by equation 2 and 3 did not strongly Thus for DN.4 or other two stranded helical interfere with our previous efforts to determine polynucleotides, the transition moment for the the heat of transition in cesium chloride.’ Thus v n * transition is perpendicular to the molecular by using equations 1, 4 , 5 and 6, a heat of transition helix axis, while the n+r* transition moment is around 1.4 kcal./mole is found, as compared with parallel to the helix axis. the value 1.55 kcal./mole based on equations 1, Dichroic studies on oriented polymer films should 2, 3, 4.l The calculated heat of transition is reveal the characteristic differences in polarization seen to deviate from the experimental value (0.58 directly. Accordingly, a series of ultraviolet absorpkcal. /mole) far more than can possibly be explained tion curves in polarized light were measured using by a non-ideal mixing of cesium and rubidium oriented films of various synthetic polynucleotides atoms. and nucleic acids. Films were prepared by placing Data for an accurate evaluation of the remaining the polymer sample on a quartz disk and dissolving correction term (the last term in equation l),which the material in a small droplet of water This takes care of the difference in specific heat of high produced a gel which was stroked until the maand low cesium chloride, do not exist. When terial had air dried. The films were optically clear, T t r - Tm is small, however, this term is quite and examination under the polarizing microscope negligible (of the order of magnitude 4 ~ p ( T t r - revealed several areas of high birefringence. The Tm)’/2Tm). From the heat content curves,a Acp disks were placed in a Cary Model 14 recording is calculated to be 0.173 cal./mole deg. a t 745OK., spectrophotometer which had been fitted with a value which entirely justifies the exclusion of this Clan Thompson prisms so that the polarized abterm from the calculations. Actually an agree(1) S. F. Mason, J Chcm. SOL.(London), 2071 (1954). ment between the observed heat of transition and (2) F. Halverson and R.C. Hirt. J. Chrm. Phys., 19,711 (1951). the heat of transition calculated from the phase (3) S. F. Mason in “Recent Work OD Naturally Occurring Nitrogen diagram cannot be obtained by choosing any rea- Heterocyclic Compounds,” Special Publications, No. 3, Chem. SOC. sonable function for Ac,. Therefore (provided (London), 1955, p. 139. (4) M. Kashd, in “The Nature and SigniGcance of n n* Transithat only a negligible amount of rubidium chloride tions,” “Symposium on Light and Life,” Johns Hopkins University TI
1
-
(7) V Hovi, Acta MctaIlurgrra, 2, 334 (1954).
Press, Baltimore, Md., 1960.
