On the partial reactivation of inactivated pantothenase from Pseudomonas fluorescens.

Partial reactivation of inactivated pantothenase (pantothenate amidohydrolase, EC 3.5.1.22) from Pseudomonas fluorescens was studied. After partial inactivation during storing, pantothenase activity is increased by 10-40% when incubated with, for instance, oxalate, oxaloacetate or pyruvate. Reactivation proceedes slowly; with oxaloacetate the stable level of enzyme activity is attained in 20-30 min. The same compounds also cause reactivation of thermally inactivated pantothenase when partial inactivation has occurred at 28-37 degrees C. The amount of the reactivating enzyme form is relatively greater the lower the temperature during inactivation, but it never exceeds 20% of the original amount of active enzyme. Also another, unstable form of pantothenase is formed in thermal inactivation. This form becomes inactivated in a few minutes after the heat treatment, at pH 6-8 and at temperatures between 0 and 10 degrees C. Reactivation causes special problems in enzyme kinetic measurements; for instance, curvature is found in the lines of Ki determination by the Dixon plot.