Carbamyl and Acetyl Phosphokinase Activities of Streptococcus Faecalis and Escherichia Coli.

Acetyl phosphate has been found to replace carbamyl phosphate as substrate for brain carbamyl phosphatase (1) ; for ornithine transcarbamylase from rat liver, frog liver, and bacteria (2, 3); for production of adenosine triphosphate with carbamyl phosphate synthetase from frog liver (3, 4); and for carbamyl phosphokinase from strain Die group D streptococci and Escherichia coli (3, 5). The ratio of the activities of brain carbamyl phosphatase with the two substrates remained constant during three purification steps, but the K,,, for acetyl phosphate was 1.1 X lop2 M and for carbamyl phosphate was 6.4 X 10e3 M and there was some difference between the pH optima of the two reactions (1). The activity of ornithine transcarbamylase from rat liver with the two substrates showed the same temperature stability (2). Carbamyl phosphate synthetase gave ATP with both substrates, the activities with the two substrates showing the same heat sensitivity and the two substrates exhibiting competitive inhibition (4). These results suggest a close relation and possibly an identity between the enzymes using acetyl phosphate and those using carbamyl phosphate. The present paper describes a comparative study of the carbamyl phosphokinase (ATP : carbamate phosphotransferase E.C. 2.7.2.2) and acetyl phosphokinase (ATP : acetate phosphotransferase E.C. 2.7.2.1) from Streptococcus fuecalis R and from Escherichia coli W which attempted to discover whether the two enzymes are identical. A comparison is made between these enzymes from the two sources. In addition, studies on the carbamyl phosphokinase of an E. coli mutant, R 185-482, which is one of a number of E. coli mutants behaving nutritionally and genetically as though they were unable to synthesize carbamyl phosphate (6lo), are reported.