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C O M M U N I C A T I O N S TO THE
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EDITOR
pool from which transformation products are iormed. The metabolism of cholesterol and its conversion to pregnenolone by adrenal homogenates have been consistently demonstrated in three additiondl experiments in approximately the same yield. The full details of these studies will be published subsequently. \Ye should like to thank Dr. Harris Iiosenkranz and &It-. Paul Skogstroni for the analysis and interprekdtions (of the infrared spectra.
vin ureidosuccinate and dihydrodrotate. Ureidosuccinate has been pictured as arising from argininosuccinate, based on the finding that the ureide carbon of citrulline3 as well as carbon dioxide4 contribute to position-2 of tissue pyrimidines in the pigeon. In the rate and in rat liver homogenates, no such incorporation from citrulline could be demonstrated, and this failure was attributed to active degradation of citrulline to urea in mammalian k-er. In the present study, pigeon and rat \\.ORCESTER FOUNDATION FOR 9 S A B A ~liver slices have been compared in regard to inEVPERIMENTAL BIOLOGY 0 HECHTER corporation into orotic acid of the ureide carbon of SHREWSBURT, MASS. D STO\E citrulline and the aniidine carbon of arginine. RECEIVED h f A Y 18, 10% L(+)-Citrulline was prepared from uren-CI4 -~ by the method of Kurtz.6 I,( +)-hrginine.HCl Fellow of the Kellogg roundatlon On leave from the ?\llnlqtry (7 was synthesized from cyanogen bromide-CI4 via of Agriculture, England 0-methylisouronium chloride.'j Both materials had specific activities of 2.84 X 106 c.p.111. per MASS SPECTRUM OF OCTABORANE mmole. Incubation was carried out essw tially Sir: according to Reichard7 using 15-18g. of pigeon or From recent mass spectrographic studies' of rat liver slices, 50 ml. of Krebs-Henseleit bicarbonvarious boron hydrides we have observed the mass ate medium supplemented with 90 mg. of glucose, spectrum of an octaborane, the existence of which 50 nig. of sodium ATP and 15 mg. of carrier orotic was first postulated by Burg and Schlesinger2 acid. Each bath also contained either 0.1 mmole of ~ - c i t r u l l i n e - C ~ ~0.5 mmole of L-aspartate or from vapor tension measurements. 0.1 mmole of L-arginine.HC1-C14 0.5 mmole of fumarate. After 4 hours of incubation at R i " , . I orotic acid was recovered from each deproteinized medium as described by R e i ~ h a r d . ~The product was characterized by ultraviolet absorption spectrum and m.p. (341-343') after recrystallization from water. All samples were combusted, and counted as barium carbonate under a thin-window 85 90 95 100 Mass number, m/e. Geiger-Mueller counter. 3t5
+
Fig. 1.-Partial
ma45
spectrum of octaborane.
The mass spectrum of octaborane from mass numbers 85 to 100 is given in Fig. 1. The dominant peak occurs a t mass number 93, and double ionimtion peaks are found in the region of mass numbers 44-48. The sharp cut-off in peak heights a t mass number 100 suggests that the composition of the octaborane is BaHI?, thus indicating that this compound belongs to the group of the (more) st>tijleboron hydrides3 In addition to the above findings we have been ahle to confirm Norton's finding of n ~ n a b o r a n e . ~
RADIOACTIVITY
+
TABLE I OROTIC ACID FROM LIVER SLICESTUDIES
O F ISOLATED
R a t liver, Pigeon liver, c.p.m. per milliatom C
Substrate L( +)-Citrulline-Cl*
+ )-Citrulline-C14 L(+ )-Argini~ie-C~~
I.(
3,390 3,040 0"
0 0 0 0
L(+)-Arginine-C14 Zero means
