Biochemical characterisation of leukaemia-associated antigen p24 defined by the monoclonal antibody ba-2

The ieukaemia-associated cell surface antigen p24/BA-2 is a single polypeptide chain with a molecular weight of 24000. Treatment with glycosidases or exposure of cells to tunicamycin failed to show any change in the molecular weight of the antigen when examined by SDS-polyacrylamide gel electrophoresis. In addition, it failed to bind to lectin affinity columns of concanavalin A, lentil lectin or Ricinus communis lectin. This is consistent with the absence of N-asparagine linked oligosaccharide chains on the antigen. Pulse-chase labelling of protein p24 shows a post-translational modification resulting in a molecular weight increase of approx. 500-1000. Alkaline treatment resulted in a decrease in molecular weight of approximately the same amount, suggesting that p24 may contain some O-glycosidically linked oligosaccharide. Protein p24 has a basicpI of 7.3 which is unchangod after neuraminidase treatment. Protein p24/Ba-2 cannot be labelled by either the lipophilic photoactivatable nitrene reagent, hexanoyldiiodo-N-(4-azido-2nitrophenyl)tyramine, or with [³²P]phosphate. This suggests that the molecule is non-integral in nature and that it does not form an intimate association with the lipid matrix. Identical molecular weights, when reduced and non-reduced antigens were compared, suggest that it contains no internal disulphide linkages and failure to detect any other band on gradient gel SDS-polyacrylamide gel electrophoresis from 5-15% suggests that it is not strongly associated with any other structure.