Primary structure of the (1 leads to 3,1 leads to 4)-beta-D-glucan 4-glucohydrolase from barley aleurone

During germination of barley grains, the cell walls of the starchy endosperm are degraded by (1→ 3,1→ 4)-β -glucanases (EC 3.2.1.73) secreted from the aleurone and scutellar tissues. The complete sequence of the aleurone (1→ 3, 1→ 4)-β -glucanase isoenzyme II comprises 306 amino acids and was determined by sequencing nine tryptic peptides (110 residues) and aligning them with the amino acid sequence deduced from a cDNA clone encoding the 291 NH2-terminal residues. Although no amino acid sequence homology with a bacterial (1→ 3,1→ 4)-β -glucanase is apparent, close to 50% homology is found with two large regions of a (1→ 3)-β -glucanase from tobacco pith tissue. The gene for barley (1→ 3, 1→ 4)-β -glucanase isoenzyme II shares with that for the α -amylase isoenzyme 1 a strongly preferred use of codons with G and C in the wobble position (94% and 90%, respectively). Both enzymes are secreted from the aleurone cells during germination. Such one-sided codon usage is not characteristic for the gene encoding the (1→ 3)-β -glucanase of tobacco pith tissue or the hor2-4 gene encoding the B1 hordein storage protein in the endosperm.