Archive image from page 577 of Currents in biochemical research, 1956;. Currents in biochemical research, 1956; twenty-seven essays charting the present course of biochemical research and considering the intimate relationship of biochemistry to medicine, physiology, and biology currentsinbioche1956gree Year: 1956 ( G. ROBERT GREENBERG tionation of the system would eventually show E to be a side product. Specific radioactivity measurements do not in themselves prove that a compound is an intermediate. Thus in studying the conversion of hypoxanthine to inosinic acid the author (12) found the fo
Archive image from page 577 of Currents in biochemical research, 1956;. Currents in biochemical research, 1956; twenty-seven essays charting the present course of biochemical research and considering the intimate relationship of biochemistry to medicine, physiology, and biology currentsinbioche1956gree Year: 1956 ( G. ROBERT GREENBERG tionation of the system would eventually show E to be a side product. Specific radioactivity measurements do not in themselves prove that a compound is an intermediate. Thus in studying the conversion of hypoxanthine to inosinic acid the author (12) found the following specific activities (counts/umole) after incubation of C-hypoxanthine with pigeon liver for 21 minutes: hypoxanthine, 4500; inosine, 2150; and inosinic acid, 1380. Furthermore inosine appeared to be a better precursor of IMP than hypoxanthine was. Accordingly it was considered rea- sonable to suggest that the reaction mechanism was via inosine perhaps as follows: ATP hypoxanthine + ribose-1-phosphate > inosine > IMP However, Buchanan and co-workers (30) have fractionated this system and their results together with the discovery of PRPP (18) provide evidence that the following holds: (1) Inosine , _ + |ATP > PRPP I at: R-5-P Hypoxanthine was more rapidly equilibrated with inosine (1) than it was converted to IMP (2), and therefore inosine had shown an intermediate specific activity in our experiments. Specific activity measurements against time may give more positive indication that a compound is an intermediate. But even when the compounds follow the typical precursor-product curves, the results are not unequivocal. More adequate evi- dence is obtained when in addition the total activity of each fraction is recorded. This allows one to observe that a net quantity of C activity has been transferred from one compound to another over a period of time. Since from the specific Dr. J. M. Buchanan, private communication. 556
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