Stability and inhibition of Aspergillus and Rhizopus lipases

A lipase (triacylglyceral aclhydrolase, EC 3.1.1.3) secreted by Aspergillus contains two chains each of molecular weight 25000, with 12 mannose, two galactose and two N-acetylglucosamine residues per chain. The average hydrophobicity is close to the mean fov globular proteins. Thermal denaturation was biphasic when followed by circular dichroism but the stability is not unusual for globular proteins, nor does partial removal of the carbohydrate affect it. (delta G=46kJ). Refolding did not occur. The inhibitory effect of 2H2O on the rate of reaction implicates a histidine in the active centre. The inhibitory effect of concanavalin A was complex but the active centre was blocked. A lipase from Rhizopus arrhizus showed immunological identity with Aspergillus lipase, but unlike that one, was not inhibited by the antiserum. Similarly it was not inhibited by concanavalin -A although Con A-Sepharose was used in its isolation. It was 4-fold as active as the Aspergillus enzyme but had low thermal stability (delta K= 16kJ). The interfacial location of lipases does not impose any special requirement on the overall structure of the enzyme.