Michael Mattey1, Davina Simoes2, Angela Brown1 and Xiaolian Fan1 1Department of Bioscience and Biotechnology, University of Strathclyde, Todd Centre, 31, Taylor Street, Glasgow, G4 0NR, Scotland. 2University of Sunderland, School of Health Sciences, Chester Road, Sunderland SR1 35D, UK.

Two esterase enzymes have been isolated, one from Candida lipolytica and one from Bacillus stearothermophilus, which are characterised by an unusually small molecular weight. The Candida enzyme is 5.7 kDa, with 56 amino acid residues and the Bacillus enzyme is 1.57 kDa, with only 17 residues (1).
In both cases the catalytic activity appears to depend on a bound metal ion, as shown by dialysis against chelating agents, ion replacement and inhibition by metal complexing agents. Specific activities are similar to reported esterase activities.
The Candida esterase has a temperature optimum of 280 , as might be expected from a mesophilic organism, but it has a half-life of 2 hours at 500 . The esterase from B.stearothermophilus is thermophilic, but whereas the optimum growth temperature is 550 the enzyme optimum is about 1200.
Both enzymes exhibit some substrate specificity. The Bacillus enzyme has no particular specificity towards the chain length of the substrate, but shows a marked activity towards the 2- position of triglycerides. The Candida enzyme shows both chain length specificity (optimum at butyl esters), as well as specificity towards the 1-position.