KINETIC CHARACTERIZATION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 PROTEASE - DETERMINATION OF INHIBITOR RATE CONSTANTS DURING DYNAMIC MONOMER-DIMER INTERCONVERSION

A numerical method was applied to a system of differential rate equati ons describing the monomer-dimer-inhibitor (M-D-I) interaction involvi ng human immunodeficiency virus type 1 protease and a peptidomimetic, competitive inhibitor, Two pairs of progress curves were obtained, one involving the M-D interaction and the other the M-D-I interaction. Ea ch pair of reactions was designed to begin with extreme conditions and end at the identical equilibrium position. The results were compared with analytical (exact mathematical) methods reported previously, Good agreement between the two methods was observed at high- and low-salt conditions for the rates of monomer association and dimer dissociation , Not surprisingly, however, the major difference was observed in the analyses involving the M-D-I interaction, since analytical methods can not account for dimer dissociation in the presence of inhibitor, While the estimates for the inhibitor off rate were comparable for high-sal t conditions (where dimer dissociation is minimized), the analytical m ethod underestimated this parameter for low-salt conditions by an orde r of magnitude, the consequence of mistaking inactive M for inactive D I. (C) 1996 Academic Press, Inc.