High-performance liquid chromatographic determination of PZ-peptidase activity

A rapid and sensitive assay method for the determination of PZ-peptidase activity is reported. This method is based on the monitoring of the absorption at 320 nm of 4-phenylazobenzyloxycarbonyl-L-Pro-L-Leu (PZ-Pro-Leu), enzymatically formed from the substrate 4-phenylazobenzyloxycarbonyl-L-Pro-L-Leu-Gly-L-Pro-D-Arg (PZ-peptide), after separation by high-performance liquid chromatography using a C18 reversed-phase column by isocratic elution. This method is sensitive enough to measure PZ-Pro-Leu at levels as low as 10 pmol, yields highly reproducible results and requires less than 5.5 min per sample for separation and determination. The optimum pH for PZ-peptidase activity was 7.5-8.0. The Km and Vmax values were 166.7 microM and 5.35 pmol/min.microgram protein, respectively, with the use of enzyme extract obtained from mouse whole brain. The approximate molecular mass of this enzyme was estimated to be 64,000 by gel filtration. PZ-peptidase activity was strongly inhibited by Zn2+, Cu2+ and p-chloromercuriphenylsulphonic acid. By using this method, PZ-peptidase activity could be readily detected in a single mouse pituitary gland. Among the tissues examined in various mouse brain regions, the highest specific activity of the enzyme was found in cerebral cortex. The sensitivity and selectivity of this method will aid in efforts to examine the physiological role of this peptidase.