Relations Between Coenzyme A and Presumptive Acyl Carrier Protein in Different Conditions of Streptococcal Growth

摘要

Exploration of the specific role of cystine in the postexponential growth of Streptococcus faecalis led to an inquiry into the fate of cellular coenzyme A (CoA) and acyl carrier protein (ACP), both of which depend for their biosynthesis on cystine and pantothenate as precursors. In S. faecalis cells labeled by growth in the presence of ¹⁴C-pantothenate, the label could be separated on the basis of solubility at pH 2.1 into two fractions of sharply differing metabolic characteristics. The fractions were not purified, but the soluble ¹⁴C behaved analytically like CoA, and the insoluble ¹⁴C was considered to represent an ACP-like entity on the basis of circumstantial evidence. The fate of these two fractions under various conditions of growth was studied. When the medium contained an excess of the needed precursors, the cellular content of CoA and ACP appeared to remain constant during exponential growth, and in a molar ratio of about 4 CoA to 1 ACP. Cellular ACP, once formed, appeared to be stable under these conditions, but CoA was degraded and replaced at the rate of approximately 20% per division period. With restrictive levels of pantothenate in the medium, initially formed CoA disappeared during growth, as a result, apparently of being converted to ACP. However, when the resulting CoA-depleted cells were returned to a medium containing enough pantothenate, resumption of normal growth was preceded by a lag period, during which rapid conversion of ACP to CoA appeared to take place.