Glycosphingolipids and Glycoproteins in the Wild‐Type and in a Non‐Aggregating Mutant of Dictyostelium discoideum

Fractionation of the phenol‐water extract from aggregation‐competent cells of Dictyosteiium discoideum resulted in the isolation of two main fractions containing two different antigen specificities, I and II, respectively. Antigen I was also obtained from growth‐phase cells of Dictyostelium discoideum. This antigen is a glycolipid, and antigen II is a glycoprotein, both containing the same sugar constituents but in different proportions: the ratio of N ‐acetylglucosamine—fucose—mannose was 12:5:2 and 12:5:6 in antigens I and II, respectively. The lipid constituents of antigen I were identified as behenic acid and 4‐hydroxysphinanine (C 18 ‐phytosphingosine) present in a ratio of 1:1. In addition, phosphate and ethanolamine were found. Under various conditions, antigen I dissociated into subfractions. The protein component of antigen II was rich in acidic and hydroxy amino acids. The carbohydrate moiety was linked through glucosamine units glycosidically to the hydroxy groups of the hydroxy amino acids. Antigen II strongly reacted with concanavalin A. Cells of a non‐aggregating mutant showed markedly increased agglutinability with wheat germ agglutinin, and changed serospecificity and electrophoretic mobility of antigen I. Extracts of cells from this mutant, harvested at a stage analogous to aggregation competence, yielded fractions similar in composition to antigens I and II. However, the N ‐acetylglucosamine—fucose—mannose ratio in this glycolipid was 12:1:3, i.e. the content of fucose was markedly reduced. With N ‐acetyl‐β‐hexosaminidase part of the N ‐acetylglucosamine was liberated from this glycolipid indicating that N ‐acetylglucosamine is a terminal sugar in the mutant antigen. Various results suggest that fucose is the terminal sugar in the wild‐type glycolipid.