β-1,4-mannosyl-glycoprotein β-1,4-N-acetylglucosaminyltransferase III activity in human B and T lymphocyte lines and in tonsillar B and T lymphocytes

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Abstract
.beta.-1,4-Mannosyl-glycoprotein .beta.-1,4-N-acetylglucosaminyltransferase III (GlcNAc-T III) catalyzes the incorporation of a "bisecting" N-acetylglucosamine (GlcNAc) residue in .beta.1-4 linkage to the .beta.-linked mannose of the core of asparagine linked-protein bound oligosaccharides (N-glycans). The activity of GlcNAc-T III was determined in Triton X-100 extracts of four human Epstein-Barr virus (EBV)-infected B-cell lines, in four T-cell lines originally established from lymphocytes of patients with acute lymphatic leukemia, and in human tonsillar B and T lymphocytes. The four EBV-transformed B-cell lines showed appreciable GlcNAc-T III activities (ranging from 3.4 to 19.0 nmol/ .cntdot. h-1 .cntdot. mg protein-1), while the tonsillar resting B lymphocytes had much less activity (0.68 nmol .cntdot. h-1 .cntdot. mg protein-1). The four T-cell lines and the tonsillar T lymphocytes had negligible GlcNAc-T III activities (ranging from 0.02 to 0.25 nmol .cntdot. h-1 .cntdot. mg protein-1). Enzyme product was identified by high resolution proton nuclear magnetic resonance spectroscopy and methylation analysis. This is the first demonstration of GlcNAc-T III activity in human lymphocytes. The presence of GlcNAc-T III in B-cell lines correlates with the reported occurrence of bisecting GlcNAc residues in the oligosaccharides of human immunoglobulins G, A1, M, and D, tonsillar class II antigens, and membrane glycoproteins from B lymphocytes. The negligible GlcNAC,-T III activity of the four human T-cell lines and of tonsillar T lymphocytes agrees with the reported absence of bisected structures in N-glycans from human T lymphocyte membrane glycoproteins.

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