Adenosine triphosphate conservation in biosynthetic regulation. Escherichia coli phosphoribosylpyrophosphate synthase.

The citrate cleavage enzyme (EC 4.1.3.8) of rat liver is inhibited by adenosine diphosphate, which appears to compete with adenosine triphosphate. This effect may ensure that fatty acids are produced only when the ATP level is high. The “energy charge” of the adenylate system, defined as (ATP + 4 ADP)/(AMP + ADP + ATP), is proposed as a fundamental metabolic control parameter. Enzymes that utilize ATP and are inhibited by ADP or AMP will yield steep curves of velocity as a function of energy charge (resembling the steep curves of velocity as a function of substrate concentration that are characteristic of many regulatory enzymes) even in the absence of multiple sites and cooperative binding.