β-Glucosidase of Penicillium funiculosum. II. Properties and mycelial binding

Abstract

The properties of two isozymes of β-glucosidase of Penicillium funiculosum (part I of this series) are described. The molecular weights of isozyme 1 was 2.3 × 10⁵ by gel filtration and 1.2 × 10⁵ by SDS gel electrophoresis, indicating two subunits. The molecular weight of isozyme 2 was unusually low for a fungal β-glucosidase: 1.6 × 10⁴ by gel filtration and 3.7 × 10⁴ in the presence of isopropanol. The two enzymes differed from other fungal β-glucosidases in their substrate specificities. They showed high activity with pNPG, cellobiose, cellotriose, cellotetraose, cellopentaose, gentiobiose, and laminarin, but were inactive with filter paper, CM cellulose, or derivatives or stabilized by bovine serum albumin and several alcohols such as butanol and propanol. It was inhibited by glucono-δ-lactone (K_i = 0.67μM) and glucose (K_i = 0.92mM). The enzyme was quantitatively adsorbed by P. funiculosum mycelium at pH 4 and the immobilized enzyme was as enzymically active as the free enzyme, but more heat stable. The binding efficiency was very high (5000 IU enzyme/g mycelium). It could be quantitatively eluted with buffers at pH 7 or by 0.02M Ca, Mg, or Al chlorides. The binding was selective, since mycelium grown on lactose could produce and also bind only β-glucosidase isozyme 1, whereas mycelium grown on cellulose could produce as well as bind both β-glucosidase isozymes as well as cellulases. Mycelial binding was unaffected by washing with EDTA or trypsinization, but was totally lost by washing with dilute KOH, HCl, or ethylenediamine.