Enzymatic synthesis of p-nitrophenyl 4(5)-O-beta-D-galactosyl-alpha-maltopentaoside as a substrate for human alpha-amylases.

Enzymatic modification at the nonreducing end D-glucosyl residue of p-nitrophenyl alpha-maltopentaoside was developed by using the transglycosylation of beta-D-galactosidase from Bacillus circulans. The enzyme regioselectively synthesized p-nitrophenyl 4(5)-O-beta-D-galactosyl-alpha-maltopentaoside (a yield of 12.0% based on the amount of p-nitrophenyl alpha-maltopentaoside added) on a preparative scale from lactose as a donor and p-nitrophenyl alpha-maltopentaoside as an acceptor. It revealed that the nonreducing end galactosyl group of p-nitrophenyl 4(5)-O-beta-D-galactosyl-alpha-maltopentaoside did not prohibit the action of human salivary and pancreatic alpha-amylases. This derivative was shown to be very suitable as a novel substrate for analytical use of human alpha-amylase assay in serum through a conjugated reaction involving glucoamylase and alpha-D-glucosidase.