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A Novel Invertase from a Thermophilic FungusThermomyces lanuginosus:Its Requirement of Thiol and Protein for Activation

Chaudhuri, Amitabha and Maheshwari, Ramesh (1996) A Novel Invertase from a Thermophilic FungusThermomyces lanuginosus:Its Requirement of Thiol and Protein for Activation. In: Archives of Biochemistry and Biophysics, 327 (1). pp. 98-106.

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Unlike the invertases from the mesophilic fungi and yeasts, invertase from a thermophilic fungus,Thermomyces lanuginosus,was unusually unstable bothin vivoandin vitro.The following observations suggested that the unstable nature of the enzyme activity in the cell-free extracts was due to the oxidation of the cysteine residue(s) in the enzyme molecule: (a) the addition of dithiothreitol or reduced glutathione stabilized invertase activity during storage of the extracts and also revived enzyme activity in the extracts which had become inactive with time; (b)N-ethylmaleimide, iodoacetamide, oxidized glutathione, cystine, or oxidized coenzyme A-inactivated invertase; (c) invertase activity was low when the ratio reduced/oxidized glutathione was lower and high when this ratio was higher, suggesting regulation of the enzyme by thiol/disulfide exchange reaction. In contrast to the activation of invertase by the thiol compounds and its inactivation by the disulfides in the cell-free extracts, the purified enzyme did not respond to these compounds. Following its inactivation, the purified enzyme required a helper protein in addition to dithiothreitol for maximal activation. A cellular protein was identified that promoted activation of invertase by dithiothreitol and it was called “PRIA” for theprotein which helps inrestoringinvertaseactivity. The revival of enzyme activity was due to the conversion of the inactive invertase molecules into an active form. A model is presented to explain the modulation of invertase activity by the thiol compounds and the disulfides, both in the crude cell-free extracts and in the purified preparations. The requirement of free sulfhydryl group(s) for the enzyme activity and, furthermore, the reciprocal effects of the thiols and the disulfides on invertase activity have not been reported for invertase from any other source. The finding of a novel invertase which shows a distinct mode of regulation demonstrates the diversity in an enzyme that has figured prominently in the development of biochemistry.

Item Type: Journal Article
Publication: Archives of Biochemistry and Biophysics
Publisher: Elsevier Science
Additional Information: copyright of this article belongs to Elsevier Science.
Keywords: Thermomyces lanuginosus;thermophilic fungi;invertase;enzyme regulation;thioldisulfide exchange reaction.
Department/Centre: Division of Biological Sciences > Biochemistry
Date Deposited: 18 Jan 2010 09:37
Last Modified: 19 Sep 2010 05:53
URI: http://eprints.iisc.ac.in/id/eprint/25084

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