Structure and function of yeast acid phosphatase

A pronounced heterogeneity of purified acid phosphatase has been observed. The size heterogeneity which was demonstrated by electrophoretic methods is in agreement with the finding that the enzyme preparation contains families of molecules differing in the carbohydrate content (38% - 70%). The charge heterogeneity was shown by isoelectric focusing indicating the existence of several slightly different protein chains in the enzyme preparation. It was found that the enzyme is a dimer with a mean molecular weight of 252000 Daltons. There are 16 N-glycosidically linked carbohydrate chains, differing in size from 15-150 mannose units, and a very small amount of O-glycosidically linked mannose. Properties of acid phosphatase deglycosilated by treatment with beta-endo-N-acetylglucosaminidase, were compared with the native enzyme and it was found that the carbohydrate chains do not play a direct role in the catalytic activity of the enzyme, but stabilize the tridimensional structure of the molecule. A drastic increase of sensitivity of the deglycosilated enzyme against proteolysis was found.