Induction and Inducers of Endo-1,4,-β-Xylanase in the Yeast Cryptococcus Albidus

Abstract

Extracellular endo-l,4-[l-xylanase synthesis in the yeast Cryptococcus alhidus is largely inducible. During growth on wood xylans the yeast produces the enzyme in amounts two orders of magnitude greater than on other carbon sources, including xylose. The enzyme can be induced in washed glucose-grown cells by xylan and fi-1,4-xylooligosaccharides. Among the oligosaccharides only xylobiose was not degraded extracellularly, therefore it appears to be the natural inducer of the enzyme. Xylobiose as a metabolisable inducer is effective at low concentrations and constant availability to cells. At high concentration of xylobiose the inductive effect is less pronounced because of catabolic repression by degradation products. Methyl fi-D-xylopyranoside was found to serve as a non-utilizable inducer of a-xylanase. The enzyme induced by the glycoside appears to be identical with that produced by the cells during growth on xylan. In the preceding paper [l] we have shown that the yeast Cryptococcus alhiclus utilizes for degradation of wood xylans to metabolizable D-xylose at least two hydrolytic enzymes : (a) an extracellular endo-I ,4-p-xylanase secreted into the culture fluid, hydrolysing xylan to series of xylose oligosaccharides, mainly to xylobiose and xylotriose; (b) a cellular fi-xylosidase (xylobiase) hydrolyzing the oligosaccharides to xylose.