Micrococcus lysodeikticus membrane ATPase. Effect of trypsin on stimulation of a purified form of the enzyme and idenfification of its natural inhibitor.

A soluble purified form of Micrococcus lysodeikticus ATPase (form BAT, from strain B, active, trypsin-stimulated) was stimulated 100% by trypsin and this stimulation was inhibited by preincubation of the protease with phenyl methyl sulphonylfluoride. This form of the enzyme was also stimulated 125-150% by filtration on Sephadex G-200. Analysis by sodium dodecyl sulphate-gel electrophoresis showed that stimulation of this form of M. lysodeikticus ATPase was always accompanied by the disappearance of a subunit of mol. wt. 25000 (epsilon subunit). It suggests that this subunit is the natural inhibitor of M. lysodeikticus ATPase. In the case of ATPase stimulation by trypsin, a partial and limited degradation of the alpha subunit was also observed. The interaction between the epsilon subunit and the rest of the ATPase complex was reversibly affected by pH, suggesting its non-covalent nature.