MEMBRANE-BOUND PROTEINASES OF HALOBACTERIUM-HALOBIUM

Cell envelopes of Halobacterium halobium contain proteolytic activities, which cleave I-125-insulin and C-14-casein with pH-optima in the alkaline range. About 50% of the intracellular proteases are strongly attached to the cell envelopes and cannot be removed by washing with 25% sodium chloride solution. This high amount of membrane-bound proteases is independent of the kind of cultivation. The main part of the envelope-bound proteolytic activity is attributed to metalloproteases, with EDTA and o-phenanthroline causing inhibition. Serine and cysteine protease inhibitors had no influence. In density gradients (consisting of Ficoll and 20% sodium chloride) proteolytic activities could be detected in two distinct bands, a minor band at a density of 1.165 and the main proteolytic activity at 1.145 g/cm3. When the cell wall was removed from the other cell envelope constituents by EDTA treatment, a single band with proteolytic activity in the density gradient at 1.145 g/cm3 was detectable. Lubrol, Brij 35 , and octyl glucoside were used for the solubilization of the membrane-bound proteases' The greatest part of them could be solubilized using 0.2% octyl glucoside. C-14-labelled bacteriorhodopsin was not cleaved by any of the intracellular or extracellular proteinases.