The structure of the yeast cell wall - II. Degradative studies with enzymes

In contrast to the use by earlier investigators of alkali in degrading the walls of yeast cells, various enzymes have now been employed for this purpose, the reaction products being characterized with the aid of chromatography. Isolated cell walls were dissolved completely by enzyme preparations from Helix pomatia and to various extents up to about 50 % by enzymes present in malt, by crystalline trypsin or by crystalline papain. In the case of the malt and snail enzymes, the rapidity of the reactions was directly proportional to the phosphorus content of the cell wall. Both glucose and N-acetylglucosamine were formed using either the malt or the snail enzymes, but no dialyzable products were detected following the action of trypsin or papain. In all cases the non-dialyzable products included both mannan and glucan fractions. Using papain, an initial phase of rapid reaction led to almost complete loss of the negative charge associated with phosphate ions. Effectively the whole of the phosphate thereby dissolved was subsequently recovered in the form of a complex with mannan and protein, which therefore probably forms part of the wall surface. On the basis of such observations, the major constituents of the wall are envisaged as con­ sisting of an insoluble glucan matrix (ca. 50%) attached by means of a protein ‘cement’ (ca. 7 %) to mannan (ca. 20%) and also to soluble glucan (ca. 10%). From the magnitude of the charge density at both the inner and outer surfaces of the wall, it is tentatively concluded that a relatively large fraction of each is occupied by mannan and a comparatively small fraction by protein.