Studies on the metabolism of ATP by isolated bacterial membranes: solubilization and phosphorylation of a protein component of the diglyceride kinase system

A soluble fraction, obtained by extracting E. coli cytoplasmic membrane vesicles with water, transfers radioactivity from γ-³²P]ATP to a protein present in this soluble fraction. The formation of the ³²P]phosphoprotein appears to be reversible. Thus the protein can transfer its ³²P to ADP to form ³²P]ATP, and the phosphate on the protein can exchange with the phosphate of ATP. Preliminary evidence indicates that the phosphate moiety is linked to a histidine residue of the protein. The Mn²⁺ and ATP dependencies of ³²P]phosphoprotein formation are almost identical to the diglyceride kinase reaction previously reported in intact membrane vesicles. Although indirect evidence supports the involvement of the phosphoprotein in the diglyceride kinase reaction, the soluble fraction catalyzes only a slow formation of ³²P]phosphatidie acid from γ-³²P]ATP and α,β-diglyceride.