Induction and characterization of an unusual α-d-galactosidase from Talaromyces flavus

An extracellular α-d-galactosidase from Talaromyces flavus CCF 2686 with extremely broad and unusual acceptor specificity is produced exclusively in the presence of the specific inducer—6-deoxy-d-glucose (quinovose). The procedure for the preparation of this very expensive substance has been modified and optimized. Surprisingly, any of other common α-d-galactosidase inducers or substrates, e.g., d-galactose, melibiose and raffinose, did not stimulate its production. The crude α-d-galactosidase preparation was purified by anion-exchange chromatography and three isoenzymes with different substrate specificities were identified. The main isoenzyme (αGal1) was further purified by cation-exchange chromatography and fully characterized. When compared with other α-galactosidases and also with other isoenzymes produced by T. flavus, it showed a markedly different regioselectivity and also negligible hydrolytic activity towards melibiose. Moreover, it was active on polymeric substrates (locust bean gum, guar gum) and significantly inhibited by α-d-galactopyranosyl azide, d-galactose, d-xylose, melibiose, methyl α- and β-d-galactopyranoside and lactose.