Studies on rat-liver glycylglycine dipeptidase

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Abstract
The glycylglycine-hydrolyzing activities present in a high-speed supernatant from homogenized rat liver have been studied. Both Co2+ and Mn2+ ions activate the hydrolysis but other bivalent cations are either without effect or inhibitory. The presence of one cation inhibits activation by others. There is significant hydrolytic activity in the absence of metal ions. This activity is inhibited by bivalent cations and by complexing agents such as EDTA and citrate. Studies of the effects of pH, reaction temperature, dialysis and time on these activities suggest the presence of at least two enzymes. Differences in substrate requirements were also observed. L-Leucine and L-isoleucine inhibit the Co2+ ion-activated enzyme, L-leucine competitively, but were less effective inhibitors of the enzyme that did not require metal ions. L-Lysine inhibited the metal-ion-free system more than the Co2+ ion system. The Km and Ki values and heats of activation were calculated from the results and these also indicate the non-identity of the metal-ion-requiring and the metal-ion-free activities.