Site of secretion and properties of endogenous endo-beta-1,4-glucanase components from Reticulitermes speratus (Kolbe), a Japanese subterranean termite

Two endo-beta-1,4-glucanase components (YEG1 and YEG2) of the endogenous cellulase from the Japanese subterranean termite, Reticulitermes speratus, were purified to homogeneity using gel filtration and hydroxylapatite chromatography, and their enzymatic properties were investigated. Using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), YEG1 and YEG2 had M-r of 42 kDa and 41 kDa, respectively. Both components had an optimal pH of 6.0, an optimal temperature of 50 degrees C and were stable at 40 degrees C for at least 30 min. Both components showed high activity on sodium carboxymethylcellulose (CMC), 73.6 U/mg protein for YEG1 and 83.4 U/mg protein for YEG2. The K-m values of YEG1 and YEG2 on CMC were 1.83 mg/ml and 1.48 mg/ml, respectively. YEG1 did not hydrolyse cellotetraose or cellotriose, whereas YEG2 hydrolysed cellotetraose to cellobiose and cellotriose to cellobiose and glucose. Both YEG1 and YEG2 hydrolysed cellopentaose to cellotriose and cellobiose. Neither component hydrolysed cellobiose. The hydrolytic products from crystalline cellulose (Sigmacell type 20) by YEG1 and YEG2 were cellobiose and a trace amount of glucose. Polyclonal mouse anti-serum raised against YEG2 crossreacted with YEG1, suggesting a common origin for both components. Using this anti-serum, Western blotting and immunohistochemistry showed the presence of YEG1 and YEG2 in the salivary glands, but not in the midgut epithelium. The data suggest that the salivary glands are the site of secretion of endo-beta-1,4-glucanase in R. speratus. (C) 1997 Elsevier Science Ltd.