Kinetic characterization of plasma membrane atpase from Saccharomyces cerevisiae

Publisher Website
Google Scholar
Abstract
Plasma membrane preparations have been isolated from spheroplasts of Saccharomyces cerevisiae, strain R XII, via lysis and subsequent differential centrifugation. These preparations are almost devoid of mitochondria) contamination. The plasma membrane ATPase is fairly stable when refrigerated, but loses activity at 8 °C and above. Below pH 5.6 the ATPase is irreversibly inactivated. The enzyme also splits GTP and ITP, although to a lesser extent. Mg2+-ions are essential as part of the reactive substrate, MgATP, and furthermore they activate the ATPase. Optimal conditions depend on substrate concentration. When the concentration of free Mg2+ ions exceeds about 0.1 mm, competitive inhibition occurs. In the range of pH 5.6–9.2 two functional groups dissociate. One, with pKb = 8.1 ± 0.1 participated in substrate binding and another one with pKb′ = 8.1 ± 0.1 is involved in substrate splitting. The experiments with group-specific inhibitors suggest that an α-amino group and a sulfhydryl residue are involved in substrate binding and conversion. Furthermore, imidazole, tryptophan and carboxyl residues may be important for the catalytic process.

This publication has 40 references indexed in Scilit: