Rabbit Muscle Adenosine 5'-Monophosphate Aminohydrolase

Abstract

Abstract Rabbit muscle 5'-AMP-aminohydrolase [EC 3.5.4.6] was sensitive to inhibition by di- and tricarboxylic acids such as succinate, maleate, fumarate, and citrate; the ADP-activated enzyme was more sensitive to these inhibitors than enzyme assayed in the presence of the activator, potassium. Citrate was competitive for ADP (Ki = 0.11 mm) and reduced the Hill slope for ADP activation from 1.7 to 1.1. Citrate also inhibited the enzyme when allowed to remain with enzyme before assay. Enzyme incubated in the presence of other metal-binding agents such as o-phenanthroline, ethylenediaminetetraacetate, 8-hydroxyquinoline-5-sulfonate, dithioerythritol, and mercaptoethanol also showed marked inhibition as a function of time of incubation before assay. Atomic absorption analysis established the presence of 2.6 g atoms of zinc per mole of native enzyme (mol wt 278,000). No significant amounts of magnesium, calcium, iron, or cobalt were observed in the purified enzyme. Removal of zinc by 8-hydroxyquinoline-5-sulfonate decreased enzymatic activity proportionally. Apo-AMP-aminohydrolase, which contained 0.45 g atoms of zinc per mole enzyme, was readily reconstituted with Zn2+, Co2+, Mn2+, and Fe2+; the cations Ni2+, Cd2+, Mg2+, and Cu2+ did not reactivate. The data suggest that AMP-aminohydrolase is a zinc metalloenzyme and that zinc is required for activity.