Abstract

Rabbit cytochrome P-450 isozymes 2 and 5 were purified from pulmonary and hepatic microsomal preparations. Purification of isozyme 5 was monitored by immunochemical methods so that contamination by isozymes 2, 4, and 6 could be avoided. Partial proteolysis of hepatic and pulmonary isozyme 5 showed minor differences in peptide formation when analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and visualized by the silver staining method. In contrast, identical patterns were observed when the peptides were transferred to nitrocellulose paper and visualized immunochemically. The differences observed between the results obtained with the two methods was apparently caused by differences in small amounts of contaminants present in both preparations. HPLC profiles of peptides formed by treatment of pulmonary and hepatic isozyme 5 with trypsin appeared to be the same. In addition, it was found that the pulmonary and hepatic isozymes had identical sequences for the first 20 NH2-terminal amino acids. Three distinct fractions of hepatic cytochrome P-450 isozyme 2 were obtained when chromatography on DEAE-cellulose was used as the final step in the purification procedure. In contrast, only a single fraction of purified pulmonary isozyme 2 was isolated by the same method. Analysis of the pulmonary and three hepatic preparations of isozyme 2 by partial proteolysis and visualization of peptides by silver staining or immunoblotting showed no differences. Analysis of tryptic digests by HPLC also produced the same results for each of the four preparations. The first 24 NH2-terminal amino acids were identical for all four preparations of isozyme 2.(ABSTRACT TRUNCATED AT 250 WORDS)