Proteinaceous Inhibitor Versus Fructose as Modulators of Pteris deflexa Invertase Activity

Author： Sampietro A.R. Isla M.I. Vattuone M.A. Sayago J.E.

ISSN： 1475-6366

Source： Journal of Enzyme Inhibition and Medicinal Chemistry, Vol.17, Iss.2, 2002-01, pp. : 123-132

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Abstract

An acid invertase from the fern Pteris deflexa Link was purified and the effect of reaction products on enzyme activity was studied. Fructose and glucose were competitive and non-competitive inhibitors of the enzyme, respectively. Since proteins suppressed glucose and fructose inhibition of the enzyme, an invertase modulation by reaction products is unlikely; nevertheless, an invertase proteinaceous inhibitor previously reported could have a role in this respect. The purified enzyme was an heterodimer M_r 90,000 Daltons composed of subunits of 66,000 and 30,000 Daltons. The enzyme had β-fructofuranosidase activity and hydrolyzed mainly sucrose but also raffinose and stachyose, with K_m of 3.22, 10.80 and 38.50 mM, respectively. Invertase activity with an optimum pH at 5.0 was present in almost every leaf fern tissue. Pinnas (sporophyll leaflets) had the higher enzyme levels. Invertase histochemical and immunochemical localization studies showed the enzyme mainly in phloem cells. Epidermis, collenchyma and parenchyma cells also showed invertase protein.