Factors affecting cyanoborohydride reduction of aromatic Schiff's bases in proteins.

Reductive alkylation of bovine serum albumin (BSA) and wool by a aromatic aldehydes and sodium cyanoborohydride has been investigated. The aldehydes used were chosen to allow convenient quantitative measurement of binding by ultraviolet spectroscopy. Alkylation of BSA occurred primarily at two highly reactive sites. Variation of time, PH, reactant concentration, and addition of urea had little effect on the extent of alkylation of BSA. However, more extensive alkylation was achieved in buffered aqueous dimethyl sulfoxide. The unusual reactivity of two epsilon-amino groups on the BSA molecule is attributed to closely placed lysine residues in the primary sequence rather than to favorable placement of unrelated, distant reactive centers. Similarly, only a few of the potentially available epsilon-amino groups of wool were observed to react.