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COMMITXICATIONS TO THE EDITOR
Vol. 80
and measurement of their absorption at 510 mp.7 h mixture of undialyzed enzyme and acetolactic acid produced 1.3 pmoles of a-ketoisovaleric acid, and the yield was almost doubled by T P N adclition. Crude extract or substrate alone, or dialyzed extract with substrate yielded only negligible arnounts. -1ddition of boiled crude extract, T P N , or DPN arid ATP restored activity of the dialyzed extract. These data demonstrate that acetolactate is a precursor of valine in S. cereuisiae, and suggest t h a t T P K (probably T P N H ) is involved with this transformation. Further efforts are proceeding for purification and fractionation of this enzyme system and for identification of several other keto acids which appeared in the chromatogram^.^
ing known partial pressures of oxygen. Oxygen, a t a known pressure, was introduced into a stainless steel bomb containing cells with polonium solutions for high pressure studies. Oxygen concentrations were calculated from the data of Zoss, Suciu and Sibbitt.' Suitable corrections were made for the dark reaction and oxidation at atinospheric pressures. The change in ferric ion concentration was followed spectrophotometrically and the rate of energy absorption in the solutions was obtained from the rate of Po21odisintegration. This rate was measured by absolute counting in a calibrated pulse ionization chamber. The full energy of the 5.3 MeV. alpha particle was assumed to have been expended within the solution. G(Fe +++) increases rapidly from its air-free value of 3.7 t o 3.2 for air-saturated solutions (2.2 X (9) This uork was supported by grants from t h e National Science -11 02).A4bove oxygen concentrations of Foundation. T h e American Cancer Society, and t h e Kational Institutes of Health. l o p 3 31, however, G(Fe+++) is nearly a linear function of the logarithm of the oxygen concentraTHEINSTITL-TE FOR CASCERRESEARCH AND MURRAY STRASSXAK tion. The highest experimental G(Fe++' ) value LASKES.4C HOSPITA4LRESEARCH IYSTITUTE obtained in this work was 9.1 f 0.4 at 1903 p.s.i. JENXIE B. SHATlOX PI?II.ADELPHIA, PEXSSYLVAKIA MILTOSE. CORSEY oxygen. The increase in G(Fe+++) with oxygen concenSIDNEY U'EISHOUSE tration is attributed t o a competition of reaction RECEIVED JAYKART 30, 1933 (1) with reactions ( 3 ) , ( 3 ) , and (4) in the mechanism of the Fricke ferrous sulfate d ~ s i m e t e r . ~ THE EFFECT OF OXYGEN O N FERRIC ION YIELDS I N H + 0 2 = HOn (1) AQUEOUS SOLUTIONS CONTAINING POLONIUM H + H = Hz (2) Sir: 9 revised G(Fef++) yield of 5.2
* 0.15 has been
obtained for a-particles from dissolved Pozlo in the aerated Fricke ferrous sulfate dosimeter. The previous value of about 6.0 reported by various worker^',^,^ is probably too high. Other lower ~ a l u e s ~ .have j * ~ been reported recently. G(Fe +&+) has been found t o vary from 3.7 f 0.2 in air-free solutions t o values approaching 10 at oxygen concentrations above 0.1 AT. Solutions studied were 3 m M in FeS04, 1 r n X in XaC1, 0.S N in HzS04and contained on the average 0.4 mc./ml. of Poz1". G(Fe+++) was independent of dose rate between 0.01 and 0.90 mc./ml. Oxygen pressures below 1 atmosphere were obtained by evacuating the samples and reintroduc(1) S . Xiller and J . Wilkinson, T r a n s . F a v a d a y SOC.,5 0 , 690 (1954). (2) 1%'. R . AIcDonell and E. J . H a r t , TIXISJ O U R N A L , 76, 2 1 2 1 (19.54). (3) hf. Haissinsky a n d M. C. Anta, Compl. rend., 836, l l C l (1953). (4) W. R. Henke, P. K. Kruys and P. P . Lifland, Project Report for t h e School of S u c l e a r Science a n d Engineering, (Argonne h'ational Laboratory) 2nd Sess'on, June 1, 1956. (3) .4.0. Allen, I n l . C o n f . o i t Peacefid Uses of Afotiiir E n e v g y , Vol. 7 , 813, United Nations N. Y..1956. ( i ; ) M , Ixfort. Com,bl. rend., 245, 1 0 2 3 (1987).
H + OH = + H T y- F e + + = H P + F e + + + H20
(3)
(4 IXTorkwith higher than 3 mill initial ferrous ion concentration [ (Fe++)o] indicates a marked dependence of G ( F e r f + ) on (Fe+f)ofor oxygen concentrations in the regions of t o lo-' ill. In contrast, at atmospheric pressures the ferric ion yield is much less sensitive t o (Fe++)". Further work is being carried out on the effect of ferrous ion concentration and on the effect of pressures above 2000 p s i . The author wishes t o express his gratitude to Drs. E. J. Hart, N. Miller and H. Fricke for valuable discussions and advice given during the course of this research which was carried out under the auspices of the United States Atomic Energy Cornmission a t Argonne National Laboratory. H
CHEMISTRY DEPARTMENT UVIVERSITY OF ROCHESTER CONRAD S ROCHESTER 20, S. Y . RECEIVED JAYUARY 31, 19%j&
TRUmORE
(7) A. Zoss. S. h'. Sucii:, W. L. Sihbitt, Tvnnr A m . S o r . M p c h . Eng., 7 6 , G!) (1%74),
