Human immunodeficiency virus-1 protease. 1. Initial velocity studies and kinetic characterization of reaction intermediates by super(18)O isotope exchange

The peptidolytic reaction of HIV-1 protease has been investigated by using four oligopeptide substrates, that resemble two cleavage sites found within the naturally occurring polyprotein substrates Pr55 super(gag) and Pr160 super(gag-pol). The values for the kinetic parameters V/KE sub(t) and V/E sub(t) were 0.16-7.5 mM super(-1) s super(-1) and 0.24-29 s super(-1), respectively, at pH 6.0, 0.2 M NaCl, and 37 degree C. By use of a variety of inorganic salts, it was concluded that the peptidolytic reaction is nonspecifically activated by increasing ionic strength. V/K increased in an apparently parabolic fashion with increasing ionic strength, while V was either increased or decreased slightly.