Studies on the formation and stability of a complex between Streptomyces proteinaceous metalloprotease inhibitor and thermolysin

The effects of certain physicochemical parameters on the formation and stability of a complex between Streptomyces proteinaceous metalloprotease inhibitor (SMPI) and thermolysin were investigated. SMPI had its lowest Ki value at a pH of around 6.5 (similar to the pH dependence of the kcat/K(m) of thermolysin catalysis), reflecting the splitting mechanism of the SMPI inhibition of thermolysin. This Ki increased with an increase in pressure, and in (Ki-1) was almost linear with respect to pressure. The volume of the reaction (delta Vcomp), which is the volume change accompanying enzyme-inhibitor complex formation, was calculated as +8.1 +/- 0.3 mL.mol-1, which has a sign opposite to delta Vcomp for neutral peptide inhibitors and acyl-peptide substrates. The temperature dependence of Ki-1 gave the reaction enthalpy (delta Hcomp) and reaction entropy (delta Scomp) of the complex formation as 34.6 +/- 1.4 kJ.mol-1 and 298 +/- 5 J.mol-1.K-1, respectively. These positive reaction volumes and reaction entropies were related to the electrostatic interactions and ionic strength dependence of Ki which corresponded to the key ionic interaction during complex formation. Complex formation with SMPI stabilized thermolysin against pressure perturbation as observed by the changes in the Trp fluorescence of thermolysin with increasing pressure. Thermal stability, however, was affected very little by complex formation with SMPI. Phosphoramidon, Cbz-Phe-Gly-NH2 and Cbz-Phe also positively affected the pressure-tolerance of thermolysin, in the following order: Cbz-Gly-Phe-NH2 < Cbz-Phe << phosphoramidon. The third compound exhibited stabilizing effects comparable with those of SMPI, which suggests that the interaction between SMPI and thermolysin was localized to the reactive site.

Peptide synthesis catalyzed by organic solvent-stable protease from Pseudomonas aeruginosa PST-01 in monophasic aqueous-organic solvent systems

The equilibrium yields of the peptide Cbz-Arg-Leu-NH2 synthesized from Cbz-Arg and Leu-NH2 using the PST-01 protease in the presence of organic solvents were investigated under various conditions. The equilibrium yields depended little on the concentration of the carboxyl component, but significantly on the concentration of the nucleophile. The optimum temperature and pH for a high equilibrium yield were 30 degrees C and greater than 5.0, respectively. Under optimum conditions the equilibrium yields were 71.6% and 87.7% in the presence of 50% (v/v) DMF and 60% (v/v) DMSO, respectively. Furthermore, the PST-01 protease also catalyzed the syntheses of the dipeptides Cbz-Lys-Leu-NH2, Cbz-Ala-Leu-NH2, Cbz-Ala-Phe-NH2, Cbz-Arg-Leu-NH2, and Cbz-Lys-Phe-NH2 with equilibrium yields of more than 60% in the presence of 50% (v/v) DMF and 50 mM sodium phosphate buffer (pH 7.0).

The effect of high pressure on thermolysin

The effects of high pressure on thermolysin activity and spectroscopic properties were studied. Thermolysin showed distinct pressure-induced activation with a maximum observed at 200-250 MPa for a dipeptide amide substrate and at 100-120 MPa for a heptapeptide substrate. By examining the pressure dependence of the hydrolytic rate for the former substrate using a high pressure stopped-flow apparatus as a mixing device under elevated pressures, the activation volume of the reaction was -71 ml mol(-1) at 25 degrees C. Delta V++ was accompanied by a negative activation expansibility and a value of -95 ml mol(-1) was obtained at 45 degrees C. A prolonged incubation of thermolysin under high pressure, however, caused a time-dependent deactivation. These changes due to pressure were monitored by several spectroscopic methods. The fourth-derivative absorbance spectrum showed an irreversible change, mostly in the tyrosine and tryptophan regions, at a pressure higher than 300 MPa. Intrinsic fluorescence and circular dichroism measurements of thermolysin in solution also detected irreversible changes. All these measurements indicated that a change occurred at higher pressures and are explained by a simple two-state transition model accompanied by a large, negative change in the volume of reaction.

Kinetic characterization of the neutral protease vimelysin from Vibrio sp. T1800

The kinetics of the hydrolysis of dipeptide and tripeptide substrates by the recently discovered neutral protease from Vibrio species T1800 (vimelysin) were studied. In the pH dependence of the apparent second-order rate constant, the pKa2 value of vimelysin (approximately 6.5) was significantly lower than thermolysin (8.3), although the pKa1 (approximately 5.1) values were comparable (5.0). The Kcat/Km(lim) parameter for hydrolysis of Fua-Gly-PheNH2 (Fua = furylacryloyl) was more than sevenfold greater than for Fua-Gly-LeuNH2. This higher specificity for Fua-Gly-PheNH2 was deduced for both Kcat and Km parameters. Fua-Phe-PheNH2 showed the highest Kcat/Km(app) value of the six substrates studied. The discrimination between Phe/Leu at the P1' site was most evident when the P1 site was not sufficiently filled. Reflecting the characteristically high proteolytic activity of vimelysin at lower temperatures [Oda, K., Okayama, K., Okutomi, K., Shimada, M., Sato, R. & Takahashi, S. (1996) Biosci. Biotech. Biochem. 60, 463-467], the Arrhenius plot of the apparent second-order rate constant for the hydrolysis of Fua-Gly-LeuNH2 showed an inverse temperature dependence; higher reaction rates were observed at lower temperatures. This was not merely due to the pKa shift nor to thermal denaturation of the enzyme coupling, but rather to the Kcat(app) parameter, which alone showed an inverse temperature dependence. A model containing two temperature-dependent forms of the active enzyme was postulated to explain this unique temperature dependence.