KINETIC-PROPERTIES OF HIV-1 PROTEASE PRODUCED BY TOTAL CHEMICAL SYNTHESIS WITH CYSTEINE RESIDUES REPLACED BY ISOSTERIC L-ALPHA-AMINO-N-BUTYRIC ACID

Human immunodeficiency virus-1 protease, produced by total chemical synthesis with the cysteine residues replaced by L-alpha-amino-n-butyric acid ([Aba(67,95)] HIV-1 PR), has been used extensively for the X-ray crystallographic structural analysis of the enzyme and its complexes utilized in drug design. Here we report kinetic studies on the synthetic enzyme. The pH optimum is 5.5 at ionic strengths of 0.1 and 1.0. The acid pH optimum is due to a decrease in binding affinity at higher pH values rather than to a reduction in catalytic efficiency. Activity is markedly increased by high ionic strength, although the major effect is on K-m and not k(cat). The effect of pH and ionic strength on the kinetic constants determined for substrates and inhibitors is demonstrated and attention is drawn to the need for assay conditions to be explicitly reported in studies on inhibitor activity. The effect of a number of inhibitors has been measured against the synthetic enzyme and a recombinant HIV-1 PR. This work shows that [Aba(67,95)] HIV-1 PR has full enzymatic activity and normal kinetic properties.