Maltotriitol Inhibition of Maltose Metabolism in Streptococcus mutans via Maltose Transport, Amylomaltase and Phospho-α-Glucosidase Activities

Abstract

Maltose glycolysis and transport in Streptococcus mutans OMZ 176 were shown to be inhibited by maltotriitol (MTL). The sugar alcohol was taken up, but was not metabolized. The phosphoenolpyruvate: maltose phosphotransferase (PEP:PTS) system activity was present in cells grown on glucose and maltose and was not inhibited by MTL. The product of the maltose PTS reaction was isolated and identified as maltose 6′-phosphate. The phospho-α-glucosidase induced by maltose hydrolyzed maltose phosphate into glucose and glucose 6-phosphate. The maltose-inducible amylomaltase which catalyses the transfer of both glucosyl and maltodextrinyl units was purified. The apparent K_m for maltose was 21.8 mM. MTL inhibited the enzyme activity on maltose (K_i 2.0 mM) and maltotriose without being itself a substrate, but transglycosylation occurred on MTL when maltoheptaose was the donor substrate. These results indicated that in strain OMZ 176, maltose transport was mediated by a PEP-dependent maltose PTS yielding maltose 6′-phosphate which subsequently was hydrolyzed by a maltose-inducible phospho-α-glucosidase. It was suggested that MTL inhibits glycolysis of maltose by reducing the rate of maltose transport and inhibiting amylomaltase and phospho-α-glucosidase activities, resulting in an accumulation of maltose 6′-phosphate.