The rabbit pulmonary monooxygenase system. partial structural characterization of the cytochrome P-450 components and comparison to the hepatic cytochrome P-450.

Two forms of rabbit pulmonary cytochrome P-450, P-450I and P-450II, are distinguished by unique peptides observed upon electrophoresis of the products of limited proteolysis (with papain or chymotrypsin) in the absence or presence of sodium dodecyl sulfate. In contrast, the peptides from the proteolytic digestions of pulmonary cytochrome P-450I are indistinguishable from those of the major form of hepatic cytochrome P-450 induced by phenobarbital (P-450PB). Electrophoresis of the fragments of P-450, and P-450II produced by treatment with cyanogen bromide also shows different peptides, whereas the peptides produced from P-450I and P-450PB are the same. The amino acid composition and P-450II is different from that of P-450I or P-450PB. P-450II is distinguished further from the other two cytochromes on the basis of amino acid composition and subunit molecular weight (either as calculated from the amino acid composition or as estimated from sodium dodecyl sulfate polyacrylamide gel electrophoresis). The sequence of the first five residues at the NH2-terminal segment of P-450I and P-450PB are identical, while that of P-450II is different.