Enzymatic properties of a galactolipase from rice bran.

Abstract

Enzymatic properties of a galactolipase (G–2) which has the highest activity in four galactolipases of rice bran were investigated. The molecular weight was estimated to be about 4 × 104 by gel filtration, and the Km value was 0.34 mm for monogalactosyldiacylglycerol. The enzyme was activated markedly by sodium deoxycholate and slightly by calcium ion, but inhibited by EDTA, Triton-X–100, sodium dodecylsulfate, NaCl and organic solvents. The enzyme lost more than 95% of its original activity when heated at 50°C for 10 min at pH 7.5. The enzyme catalyzed the hydrolysis of both galacto- and phospholipids. The relative hydrolysis rates decreased in the order of digalactosyldiacylglycerol > monogalactosylmonoacylglycerol > monogalactosyldiacylgiycerol > lysophosphatidylcholine > phosphatidylcholine. The enzyme catalyzed the hydrolysis of fatty acid ester bonds at both C − 1 and −2 positions of galactolipid. It is suggested that serine and cystine residues are important to the enzymic activity.