Purification and properties of Mg2+-Ca2+ adenosinetriphosphatase from Escherichia coli

A procedure for the purification of Mg(2+)-Ca(2+) adenosinetriphosphatase (EC 3.6.1.3) from E. coli, yielding relatively large amounts of highly active enzyme, is described. The enzyme consists of four nonidentical subunits. Trypsin treatment of purified enzyme yields a preparation consisting exclusively of the two larger subunits, which are sufficient for ATPase activity. Purified enzyme is inhibited by 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole; this inhibition is reversed by dithiothreitol, and the diazole is found preferentially associated with the beta-subunit of the enzyme. Antibody prepared against the trypsin-treated enzyme inhibited various ATP-dependent reactions as well as membrane-bound ATPase itself.