LYTIC ENZYMES IN THE DIGESTIVE JUICE OF HELIX POMATIA: CHITINASES AND MURAMIDASES

Abstract

Two enzymes in the digestive juice of Helix pomatia are responsible for most of the juice's lytic activity towards Micrococcus lysodeikticus. The enzymes were isolated by gel filtration in polyacrylamide (Biogel P-30) followed by gradient displacement from Amberlite CG50. Both enzymes hydrolyze mucopeptide from the cell wall of M. lysodeikticus and the hydrolysis is accompanied by liberation of soluble reducing sugar. The reducing end groups were shown to be N-acetyl-muramic acid residues by evidence that the hexitol of muramic acid is the only amino sugar hexitol which is released from the mucopeptide by the reaction sequence: enzymic hydrolysis, reduction with sodium borohydride, and acid hydrolysis. Thus both enzymes are muramidases. One enzyme (designated muramidase I), like egg-white lysozyme, readily hydrolyzes hydroxyethyl chitin; the other enzyme (muramidase II) does not. Muramidase II is the more basic of the two enzymes; its isoelectric point in 0.05 M hydrochloric acid – Tris buffer is close to pH 9.0. The molecular weights of muramidase I and muramidase II were estimated by the Archibald method to be approximately 21,000 and 24,000 respectively; both estimates assume a partial specific volume of 0.72 cc/g.