Yeast Epiarginase Regulation, an Enzyme-Enzyme Activity Control

Abstract

In the presence of ornithine and arginine, ornithine carbamoyltransferase (OTCase) and arginase form a one-to-one enzyme complex in which the activity of OTCase is inhibited whereas arginase remains catalytically active. The mechanism by which these nonallosteric enzymes form a stable complex triggered by the binding of their respective substrates raises the question of how such a cooperative association is induced. Analyses of mutations in both enzymes identify residues that are required for their association, some of them being important for catalysis. In arginase, two cysteines at the C terminus of the protein are crucial for its epiarginase function but not for its catalytic activity and trimeric structure. In OTCase, mutations of putative ornithine binding residues, Asp-182, Asn-184, Asn-185, Cys-289, and Glu-256 greatly reduced the affinity for ornithine and impaired the interaction with arginase. The four lysine residues located in the SMG loop, Lys-260, Lys-263, Lys-265, and Lys-268, also play an important role in mediating the sensitivity of OTCase to ornithine and to arginase and appear to be involved in transducing and enhancing the signal given by ornithine for the closure of the catalytic domain.

Selective control of amino acid metabolism by the GCN2 eIF2 kinase pathway in Saccharomyces cerevisiae

“…Both arginine anabolism and catabolism are linked to the urea cycle. In the case of the urea cycle, cell uses the available arginine, ornithine, and citrulline to effect enzymatic activity in addition to Gcn4p to regulate metabolic flux [13,26]. While we were unable to completely eliminate the growth defect in gcn2 Δ strains with supplements, partial growth restoration was possible in media containing high concentrations of ornithine.…”