Selective covalent modification of newly synthesized activation-induced sialoglycoconjugates on the T lymphocyte membrane

Resting human lymphocytes were oxidized by periodate and subsequently reduced with borohydride to block the aldehydes formed. The cells were then incubated for 24 or 48 hours with (or without) the mitogenic lectin phytohemagglutinin. A second oxidation with periodate at the indicated times resulted in strong surface-aldehyde formation in samples incubated with the mitogen, compared to control samples which exhibited very low quantities of aldehydes. The data show that this elevation in aldehyde formation was strictly dependent on protein synthesis, similarly to the appearance of Tac antigen in these cells. Cell surface aldehydes were detected in flow cytometry with a fluoresceinated hydrazide molecule and electrophoretically with biocytin hydrazide in conjunction with 125I-streptavidin. The proposed method for the elimination of the chemical reactivity of carbohydrates from the surface of resting lymphocytes thus enabled the selective covalent modification of newly synthesized sialoglycoconjugates formed upon a mitogenic trigger. The data also suggest the existence of a very low turnover rate of sialoglycoconjugates on the resting lymphocyte membrane.