The structure of the yeast cell wall - I. Identification of charged groups at the surface

Abstract

The electrophoretic mobility of various strains of Saccharomyces cerevisiae and S. carlsbergensis over the range pH 2 to 9 and at constant ionic strength ( I = 0.005) varies from about + 0·5 to — 1·5 µ , s -1 (V /cm ) -1 , values of an order indicating that the fraction of the cell surface occupied by ions is probably rather small. Both intact cells and the cell walls isolated from them behave similarly on electrophoresis and in a manner varying with the strain of yeast. It is the composition of the wall therefore which determines the electrophoretic properties. Two general effects (I and II) of change of pH on electrophoretic mobility were distinguished as characterizing certain strains of yeast, although in other cases they were encountered together. In the first type (I), the mobility was nearly independent of the pH and corresponded to a negative charge. As such charges were lacking from yeasts grown in media deficient in phosphate, and as the mobility of the isolated cell wall appeared to be directly related to its phosphorus content, the negative charge may be attributed to combined phosphate forming part of the fixed structure of the cell wall. In the second form of behaviour (II) the mobility varied continuously between pH 3 and 6, with an alteration in charge from positive to negative at about pH 4. In this case the charged groups are tentatively attributed to protein, as material of this nature was removed together, apparently, with the groups themselves when cell walls were treated with alkaline solutions.