NEUTRAL ALPHA'-MANNOSIDASE OF HUMAN B-LYMPHOID AND T-LYMPHOID CELLS

The presence of neutral alpha-mannosidase was detected in normal and pathological human lymphoid cells; its specific activity was approximately the same in different types of cells, with the exception of the B cells of B-CLL* patients, where it was a little higher. The acid alpha-mannosidase activity was also determined in these lymphoid cells. The activity ratio of these two alpha-mannosidases in pathological B and T cells differed substantially. Although acid alpha-mannosidase activity predominated in T cells, the acid alpha-mannosidase activity in B cells was significantly reduced, and neutral alpha-mannosidase activity predominated. This may indicate a difference in the nature of the metabolism of mannose-containing compounds in these two types of lymphoid cells. A comparative study was made of the properties of partially purified neutral alpha-mannosidase preparations from pathological B and T cells. In both cell types, neutral alpha-mannosidase was localized in the cytosol. The enzyme was very labile and was stabilized by Mn2+ ions and and by dithiothreitol. Neutral alpha-mannosidase from both cell types was activated by Co2+ ions; Zn2+ ions and EDTA inhibited the enzyme. This showed that neutral alpha-mannosidase is a metal-dependent enzyme. Neutral alpha-mannosidase of lymphoid cells was inhibited by swainsonine, the enzyme of the B cells to a greater degree than the T cell enzyme. This suggests that the neutral alpha-mannosidases of B and T lymphoid cells are similar but not identical.