Evidence for the essential histidine residues in geranylgeranyl transferase type I from bovine testis

Geranylgeranyl transferase was purified 30,000-fold by sequential use of 30-50% ammonium sulfate fractionation, Q-Sepharose anion exchange chromatography, Phenyl Superose hydrophobic interaction chromatography, Sephacryl S-300 gel filtration chromatography, and peptide (YREKKFFCAIL) affinity chromatography. Geranylgeranyl transferase, when incubated with diethyl pyrocarbonate (DEPC), a histidine-specific reagent, shows time-dependent inactivation, and the activity is restored by the addition of neutral hydroxylamine. The inactivation follows pseudo-first order kinetics with a second order rate constant of 0.319 M-1min-1. The overall results thus provide evidence that a histidine residue in the active site is involved in the catalytic mechanism of the geranylgeranyl transferase reaction.