Enzyme and Nucleic Acid Formation During Synchronous Growth of Rhodopseudomonas spheroides

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Abstract
The synthesis of various cell components was examined during the anaerobic photosynthetic growth of synchronous populations of R. spheroides. Net DNA, RNA and protein increased continuously as did the rate of incorporation of radioactive precursors into protein. The rates of incorporation of radioactive precursors into RNA and DNA were marked by abrupt discontinuities which may represent changes in rates of synthesis or fluctuations in precursor pools. Although the synthesis of bacteriochlorophyll occurred in a continuous manner, those enzymes examined which are involved in the synthesis of tetrapyrroles (succinyl CoA thiokinase, S -aminolevulinic acid synthetase and 6-aminolevulinic acid dehydrase) increased discontinuously. Two other enzymes not involved in tetrapyrrole biosynthesis were examined. Alkaline phosphatase increased in a stepwise manner during the division cycle, whereas the synthesis of ornithine transcarbamylase increased rapidly before leveling off for a period of time until synthesis began again. In each instance of discontinuous enzyme synthesis, increases occurred at regular and characteristic times during the divi- sion cycle. Precipitation by (NH4)2 SO4 was employed to remove low molecular weight end product inhibitors from enzyme preparations. The stepwise increases in enzyme activity may not be affected by periodic end product inhibition. A temporal map of enzyme synthesis during the division cycle was constructed. Both [delta] -aminolevulinic acid synthetase and 5 -aminolevulinic acid dehydrase appeared early in the division cycle, whereas alkaline phosphatase and succinyl CoA thiokinase appeared later.