Comparative study of nuclear and cytoplasmic glycogen isolated from mutant HD33 ascites cells

Mutant cells of the HD33 subline of the Ehrlich‐Lettré ascites tumor synthesize and store glycogen mainly intranuclearly, when growing in vivo, and exclusively in the cytoplasm, when permanently cultivated as a suspension cell strain. To investigate whether there exist differences between glycogen of nuclear and cytoplasmic origin, the ultrastructure and the biophysical and biochemical properties of glycogen from in vivo and in vitro grown HD33 ascites cells were compared. Pronounced heterogeneity and differences in glycogen particle ultrastructure were evident in situ and after isolation of the native, high‐molecular polysaccharide. Nuclear glycogen contains a fraction of heavier molecules (up to 2 × 109) and larger particles (up to 340 nm) which could not be found in the cytoplasmic preparations, which contained only particles smaller than 140 nm. The subparticles of β‐type are similar in both nuclear and cytoplasmic glycogen. The absorption spectra and glucose analysis after degradation with phosphorylase and debranching enzyme indicate that nuclear glycogen has a higher degree of branching, associated with a decrease in the average chain length between the branching points, and shorter external polyglucosidic chains than cytoplasmic glycogen. This is the first report about the analysis and properties of isolated nuclear glycogen.