CHARACTERIZATION OF A K-ATPASE FROM LACTOBACILLUS-HELVETICUS ATCC-15009()

Lactobacillus helveticus ATCC 15009 (wildtype) membrane preparations h ydrolyzed Mg2+-ATP as a function of K+ concentration (2-200 mM). Mg2+- ATP hydrolysis by L. helveticus membranes was strongly inhibited in th e absence of exogenous K+, while it amounted to 6 nmol ATP hydrolyzed min(-1) (mg membrane protein)(-1) at 50 mM KCl (saturating conditions) and pH 7.2. The K+-dependent ATPase of L. helveticus displayed a rela tively high affinity for potassium ions (K-m= 800 mu M) and was not af fected by pretreatment of membranes with N,N'-dicyclohexylcarbodiimide . Membrane preparations were subjected to hypotonic shock to obtain a maximum yield of open profiles. The formation of a maximum level of en zyme-phosphate complex with a molecular mass of approximately 82 kDa w as induced upon treatment of L. helveticus membrane preparations with low concentrations of [gamma-P-32]ATP in the presence of K+ and La3+ i ons and was visualized by acidic SDS-PAGE. It was concluded that L. he lveticus membranes contain an inwardly directed K+ pump whose presence is discussed in terms of its putative role in cytoplasmic pH regulati on.