engleski

Partial purification and characterization of a novel L,D-endopeptidase from guinea pig serum

Peptidoglycans are common constituents of bacterial cell walls, conferring physical integrity upon the cell, but also exhibiting versatile biological activities including immunomodulating and antitumor properties. Peptidoglycan monomer (PGM) from Brevibacterium divaricatum is disaccharide pentapeptide of the following composition: GlcNAc-MurNAc-L-Ala-D-isoGln-mesoDAP-(NH2)-D-Ala-D-Ala(1). The hydrolitic enzyme N-acetylmuramyl-L-alanin amidase catalyses the hydrolysis of the PGM into disaccharide and pentapeptide portion. This enzyme has been detected in human, mouse, rabbit, bovine and sheep sera(2). The same enzymatic activity was found in the guinea pig serum, but in addition we recently discovered different enzymatic activity that cleaves the pentapeptid into alanin and the respective tetrapeptide. Such activity has not been detected into mammalian sera so far, althought the presence of complementary bacteriolitic enzymes has been reported. We now report the partial purificetion of a novel enzyme from guinea pig serum on DEAE-Sepharose fast flow. Enzymatic reaction was followed using the pentapeptide as a substrate, by thin layer chromatography and high performance liquid chromatography. Mass spectroscopy of the resulting tetrapeptide reveald that the novel enzyme cleaves L-alanine from the NH2-terminus of the pentapeptide, alowing us to assume that the discovered enzyme might be L,D-endopeptidase. Also, different derivatives of the pentapeptide were tested as a potential substrates for this enzyme. (1) Keglević D., Ladešić B., Tomašić J., Valinger Z. and Naumski R., Biochim. Biophys. Acta 585 (1979)281-293 (2)Valinger Z.,Ladešić B. and Tomašić J., Biochim. Biophys. Acta 701 (1982)63-71

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