Comparison of purified acid phosphatase allozymes inDrosophila virilis: Differences in carbohydrate content and composition of the allozymes

Three acid phosphatase (EC 3.1.3.2) allozymes (ACPH¹, ACPH², and ACPH⁴) ofDrosophila virilis show different activities as measured by electrophoretic techniques. Recently, it was suggested that these differences are attributable to the variable ability of the allozymes to be incorporated into lysosomes (Narise, S.,Genet. Res. Cambr., 45:143, 1985). Immunoelectrophoresis demonstrated that the activity differences between these electrophoretic variants coincided with differences in the amount of the enzyme protein in soluble fractions but not in whole cell-free extracts. These results support the idea that acid phosphatase allozymes inD. virilis are cell-localization variants. We examined the problem by structural analysis of both the protein and the carbohydrate moieties of these allozyme glycoproteins, since lysosomal enzymes are known to become localized in lysosomes through their carbohydrate moieties. The three ACPH allozymes were purified to homogeneity from their respective homozygotes and compared with respect to amino acid composition and carbohydrate content and composition. Amino acid compositions were similar, while content and compositions of neutral sugars were significantly different. The neutral sugar content of ACPH¹ was 9.2%; that of ACPH², 21.0%; and that of ACPH⁴, 7.3%. A trace of hexosamines, but noN-acetylneuraminic acid, was found in the ACPH allozymes. Isoelectric points varied corresponding to their electrophoretic mobilities, which were not changed by treatment with alkaline phosphatase and neuraminidase.