A TRANSGLUCOSYLASE OF STREPTOCOCCUS BOVIS

Abstract

1. A transglucosylase has been separated from the alpha-amylase of Streptococcus bovis by chromatography of the cell extract on DEAE-cellulose. 2. The transglucosylase can synthesize higher maltodextrins from maltotriose, but maltose, isomaltose and panose do not function as donors. 3. Iodine-staining polysaccharide may be synthesized from maltotriose provided that glucose is removed. Synthesis from maltohexaose results in dextrins of sufficient chain length to stain with iodine, but again maltodextrins of longer chain length are formed when glucose is removed from the system. 4. The transglucosylase degrades amylose in the presence of a suitable acceptor, transferring one or more glucosyl residues from the non-reducing end of the donor to the non-reducing end of the acceptor. With [(14)C]glucose as acceptor the maltodextrins produced were labelled in the reducing glucose unit only. 5. The acceptor activities of 25 sugars have been compared with that of glucose. Maltose has 50%, methyl alpha-glucoside has 15%, isomaltose and panose each has 8% and sucrose has 6% of the accepting efficiency of glucose. Mannose and sorbose also had detectable activity. With the exception of maltose all these sugars produced a different series of dextrins from that obtained with glucose. 6. It was concluded that S. bovis transglucosylase transfers alpha-(1-->4)-glucosidic linkages in the same manner as D-enzyme, but some differences in specificity distinguish the two enzymes. Unlike D-enzyme, S. bovis transglucosylase can transfer glucosyl units, producing appreciable amounts of maltose both during synthesis from maltotriose and during transfer from amylose to glucose. 7. No evidence was found that the transglucosylase was extracellular. The enzyme is cell-bound, and is released by treatment of the cells with lysozyme and by suspension of the spheroplasts in dilute buffer. 8. The transglucosylase may be responsible for the storage of intracellular iodophilic polysaccharide that occurs when the cells are grown in the presence of suitable carbohydrate sources.