Characterization of a Bacterial Laminaribiose Phosphorylase

Bacterial laminaribiose phosphorylase (LBPbac) was first identified and purified from cell-free extract of Paenibacillus sp. YM-1. It phosphorolyzed laminaribiose into a-glucose 1-phosphate and glucose, but did not phosphorolyze other glucobioses. It slightly phosphorolyzed laminaritriose and higher laminarioligosaccharides. The specificity of the degree of polymerization of the substrate was clearly different from that of the enzyme of Euglena gracilis (LBPEug): LBPbac was more specific to laminaribiose than LBPEug. It showed acceptor specificity in reverse phosphorolysis similar to LBPEug. Cloning of the gene encoding LBPbac (IbpA) has revealed that LBPbac is a member of the glucoside hydrolase family 94, which includes cellobiose phosphorylase, cellodextrin phosphorylase, and N,N'-diacetylchitobiose phosphorylase. The genes that encode the components of an ATP-binding cassette sugar transporter specific to laminarioligosaccharides were identified upstream of IbpA, suggesting that the role of LBPbac, is to utilize laminaribiose generated outside the cell. This role is different from that of LBPEug, which participates in the utilization of paramylon, the intracellular storage 1,3-beta-glucan.