Phosphorylation coupled with anaerobic breakdown of citrulline

Abstract

Phosphorylation of ADP coupled with breakdown of citrulline to ornithine by a cell-free extract of Streptococcus faecalis was studied quantitatively. A mixture containing citrulline and ADP releases CO2, forms ATP, and removes ADP and inorganic phosphate, the 4 changes being approx. equivalent. Results agree with the view that the overall change is: citrulline + ADP + phosphate[forward arrow]ornithine + CO2 + NH3 + ATP. p32-labeled potassium dihydrogen phosphate was used to distinguish between ATP formed from ADP by the action of adenylate kinase (myokinase) and by synthesis involving inorganic phosphate. Appearance of P32 in ADP, and in both of the labile phosphates of ATP, but not in AMP, indicates the presence of adenylate kinase in extracts of S. faecalis. Fission of citrulline according to the reaction formulated above represents a new type of coupled phosphorylation leading to formation of pyrophosphate bonds of ATP.