THERMITASE, A THERMOSTABILE SERINE PROTEASE FROM THERMOACTINOMYCES VULGARIS - INTERACTION BETWEEN THE ACTIVE-CENTER AND THE SH-GROUP OF THE ENZYME

  • 1 January 1982
    • journal article
    • research article
    • Vol. 41  (2-3) , 137-144
Abstract
Modification of the serine and histidine residues in the active center of [T. vulgaris] thermitase with DFP or L-tosylamide-2-phenylethyl chloromethylketone (TPCK), and of the only SH-group of the enzyme with Hg compounds causes a loss of 4-nitrophenylacetate hydrolyzing activity. While modification of the cysteine residue prevents the reaction of serine and histidine residues in the active center of the enzyme with DFP and TPCK, respectively, the Hg2+- and CF3Hg+-binding to the SH-group after modification of essential amino acid residues in the active center is retained. To elucidate the interaction of the SH-group with the active center, the modified products of thermitase were investigated for their thermostability. Ca2+ had a stabilizing effect on all the modified products of thermitase, as well as on the native enzyme. Simultaneous modification of the cysteine and serine leads to an increase in thermostability of thermitase, while double modification at the cysteine and histidine residues causes destabilization of the enzyme.