Thermal inactivation of pantothenase from Pseudomonas fluorescens

Protection of pantothenase (pantothenate amidohydrolase, EC 3.5.1.22) against thermal inactivation by ligands was studied. The protective properties of 162 different small-molecule compounds were tested to find the most effective compounds. The best protective results were obtained with oxamate, 3-oxoglutarate, 2-oxomalonate, oxalate and oxaloacetate, in that order. The protection constants (eta) of certain metabolic intermediates were estimated using differential thermal inactivation. Generally they were observed to be lower than the corresponding inhibition constants. The deltaH of the oxalate binding derived from eta values was --165 kJ/mol. Normally, the activation energy of thermal inactivation of pantothenase in the absence of protective compounds is 220 kJ/mol, and the protective ligands enhance the measured activation energies of inactivation.