THE DEVELOPMENT OF β-D-GLUCANASES DURING THE GERMINATION OF BARLEY AND THE EFFECT OF KILNING ON INDIVIDUAL ISOENZYMES†

Visualization of barley beta-glucan degrading isozymes after gel isoelectric focusing

A simple method to study the polymorphism of barley (Hordeum vulgare L.) beta-(1-3,1-4)-glucanases (specific enzymes of barley beta-glucan hydrolysis) is described. Proteins of a crude extract of germinated barley kernels were separated in an immobilized pH gradient in two pH ranges (pH 3-10.5 and pH 4-7). beta-glucanases were visualized by contact printing with a polyacrylamide gel containing beta-glucan or lichenan. Patterns of beta-glucanases were revealed by staining with Congo Red with resultant clear zones on a stained background. Various conditions of germination, extraction and visualization were investigated. New isozyme bands could be detected and their nature and origin discussed.

Differences in the thermostabilities of barley (1----3,1----4)-beta-glucanases are only partly determined by N-glycosylation

Barley (1----3,1----4)-beta-glucan 4-glucanohydrolase (EC 3.2.1.73) isoenzyme EII carries 4% by weight carbohydrate and is more stable at elevated temperatures than isoenzyme EI, which has no associated carbohydrate. The relationship between carbohydrate content and thermostability has been investigated by treatment of the two isoenzymes with N-glycopeptidase F (EC 3.5.1.52). Removal of carbohydrate from isoenzyme EII results in a decrease in the enzyme's thermostability, but treatment of isoenzyme EI with the N-glycopeptidase F has no effect. In addition, removal of a single N-glycosylation site in isoenzyme EII (Asn190-Ala-Ser) by site-directed mutagenesis of the corresponding cDNA led to a reduction in thermostability, while the introduction of this site into isoenzyme EI enhanced stability. We conclude that N-glycosylation of Asn190 enhances the stability of isoenzyme EII at elevated temperatures, but that other factors related to their primary structures also contribute to the differences in thermostabilities of the barley (1----3,1----4)-beta-glucanases.