Esterase, active serine, detection

The serine protease from Thermus caldophilus strain GK-24 [292] gave maximum activity at 90 °C in 20 min assays and had a broad pH optimum with casein as substrate. The enzyme showed hydrolytic activity on some small peptide substrates (e.g. CBZ-L-leu-L-tyr-NHj) and also possessed esterase activity. Hydrolysis of synthetic chromogenic peptides and esters is also a property of the recently described serine protease, caldolase, from Thermus strain ToK3 [293]. This enzyme contained 10% carbohydrate and four disulphide bonds, but neither calcium nor zinc were detected in the purified enzyme. Thermostability of the enzyme was high in 0.4 M NaCl, but in low ionic strength buffer rapid thermal denaturation occurred at 75 °C. Work has also been undertaken in this laboratory... 

Caldolysin is the trivial name of the serine proteinase from T. aquaticus strain T351 [284]. This enzyme did not have detectable esterase aetivity and hydrolysis of small peptides of less than four amino acids was not observed. The enzyme was highly stable in the presenee of ealcium ions. Caldolysin bound six calcium ions per molecule of enzyme, there being both high and low affinity binding sites [285]. Stability of apocaldolysin (i.e. caldolysin treated with EDTA to remove all calcium ions) was restored upon incubation with either calcium or lanthanide ions, the latter giving a lanthanide-caldolysin complex more stable than the native enzyme. Strontium ions were the only other divalent metal ions tested that could restore more than 50% activity. 

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