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SUMMARY: The paths of transfer of phosphate groups during uptake of inorganic orthophosphate by Micrococcus pyogenes var. aureus (strain Duncan) have been studied by following the incorporation of 8aP-labelled phosphate groups into the phospholipid (LP), acid-soluble inorganic ( AI) and organic (AO), deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and glycerophospho-protein complex (PGP) fractions of the cells. In resting cells a strictly reciprocal exchange of inorganic phosphate across the osmotic barrier is half complete in 70 min. During respiration or growth, phosphate moves inward through the osmotic barrier at the same rate as during rest, but the outward movement is abolished. Phosphate accumulates mainly in the AI, A0 and LP during respiration, but in all the fractions during growth. Most of the phosphate of the organic fractions is drawn through the AI. The RNA is formed from the nucleotides of the AO, while the DNA phosphate is derived either directly from the A1 or from intermediates in the AO. Little or no turnover of RNA or DNA phosphate occurs during growth, and phosphate is not transferred directly or indirectly from RNA to DNA or vice versa. The PGP, although the major constituent of the mechanically rigid cell envelope, does not participate as a whole in phosphate transfer reactions during rest or respiration; but during growth the amount of PGP increases in proportion to the expansion of cell envelope area. The LP phosphate exhibits rapid turnover during respiration and growth. The work to be described here was undertaken to obtain information about the process of assimilation of inorganic orthophosphate by Micrococcus pyogenes var. uurew (strain Duncan). The aim was to trace with the paths of entry of phosphate from the suspension medium into the main phosphate fractions of the cells when (a) resting, (b) respiring, and (c) growing. The phosphate fractions selected for study were : the cold 5 yo trichloroacetic acid-soluble inorganic (AI) and organic (AO), the phospholipid (LP), deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and glycerophospho-protein complex (PGP) fractions of the cells; and the inorganic phosphate of the medium (mI). All are well known except the PGP, the major constituent of the mechanically rigid cell envelope of M. pyogenes, formerly called XSP (Mitchell & Moyle, 1951 b). Essentially the problem was the same as that of Juni, Kamen, Reiner & Spiegelman (1948) in their studies of phosphate assimilation by baker's yeast. Our treatment differs, however, in one important respect. Spiegelman and his collaborators interpreted their findings in the usual terms of phosphate ' turn- over ' inferred in many cases from determinations of relative specific activity alone. Much more definite information may be obtained from estimations of the total P and contents of the phosphate fractions: moreover, interpreta- tion becomes easier and less ambiguous because the total P and contents

Paths of Phosphate Transfer in Micrococcus pyogenes: Phosphate Turnover in Nucleic Acids and other Fractions