摘要：Pyroglutamyl aminopeptidase I (PAP-I) is known for specifically removing the L -pyroglutamate ( L -pGlu) residue from the amino terminus of L -pGlu proteins and peptides. In general, substrate recognition of PAP-I as to L -pGlu moiety is tightly regulated. However, we recently identified PAP-I as a metabolic enzyme of an organic nitrate compound, RS-7897, which contains L -2-oxothiazolidine-4-carboxylic acid ( L -OTCA). L -OTCA is a latent sulfhydryl group, which has moiety structurally related to L -pGlu. In this study, we investigated the substrate specificity of PAP-I toward modified L -pGlu-containing substrates using recombinant rat, mouse and human PAP-Is. PAP-I was tolerant of replacement of a carbon atom at the 4-position of the L -pGlu moiety by a sulfur atom ( L -OTCA), an oxygen atom ( L -2-oxooxazolidine-4-carboxylic acid, L -OOCA) and an NH group ( L -2-oxoimidazolidine-4-carboxylic acid, L -OICA). The K m values for rat PAP-I in hydrolyzing L -pGlu– L -Ala, L -OTCA– L -Ala, L -OOCA– L -Ala and L -OICA– L -Ala were 0.057, 0.43, 0.71 and 0.42 m M , respectively. Similar results were observed in mouse and human PAP-Is as well. Moreover, the hydrolysis of RS-7897 in rat and mouse liver cytosols were both completely inhibited by an antibody against rat PAP-I, strongly suggesting that PAP-I is solely involved in the hydrolysis of L -OTCA-containing compounds in rat and mouse liver cytosols.
关键词：pyroglutamyl aminopeptidase I; L -pyroglutamate;substrate specificity; L -2-oxothiazolidine-4-carboxylic acid
