STUDIES OF THE TRANSGLYCOSYLATION REACTION CATALYZED BY THE DECYCLING MALTODEXTRINASE OF FLAVOBACTERIUM SP NO-92 WITH MALTOOLIGOSACCHARIDES AND CYCLODEXTRINS

The degradation pattern of malto-oligasaccharides (from maltotriose to maltooctaose) and cyclodextrins by the decycling maltodextrinase of Flavobacterium sp. no. 92 was studied. Both the activity and the affinity of the enzyme increased up to maltohexaose, confirming that the active site comprised six subsites. The molar catalytic activity with cyclomalto-hexaose was insignificantly less than that with maltohexaose, but the Michaelis constants determined for the cyclodextrins were 4.4 times lower than those of the malto-oligosaccharides with corresponding lengths. The molecular binding affinities of maltohexaose and cyclomaltohexaose were found to be -28 and -31.5 kJ.mol(-1), respectively. The maltodextrinase displayed considerable transglycosylation activity, in which glucosyl-transfer predominated. The molar concentrations of transglycosylation products were highest with maltotetraose, but decreased linearly with increasing lengths of substrate. Likewise, the concentration of the individual products decreased linearly for every substrate. The molar concentrations of the individual hydrolysis products (except for glucose) were comparable in the digests of all the substrates assayed, and decreased linearly with increasing lengths. The amounts of glucose decreased linearly with increasing length of substrates, which was ascribed to the length-dependent binding modes of substrates at the active site. The comparison of the actual amounts of hydrolysis and transglycosylation products formed with maltotriose to maltopentaose with those calculated on the basis of substrate consumption suggested that the transglycosylation rates with these substrates were higher than the calculated values, i.e., the bimolecular reaction was likely to be vital to their degradation. Less transglycosylation products, but larger amounts of the ''open-chain'' substrate were observed in the digests of cyclomaltodextrins. The accumulation of the open-chain substrate might be due to the higher affinity of the enzyme for cyclomaltodextrins, thus preventing the resulting malto-oligosaccharides from being degraded in the presence of an excess of the cyclic substrate.