Invertase activity associated with the walls of Solanum tuberosum tubers

Three fractions with invertase activity (beta-D-fructofuranoside fructohydr olase, EC 3.2.1.26) were isolated from mature Solanum tuberosum tubers: aci d soluble invertase, invertase I and invertase II. The first two invertases were purified until electrophoretic homogeneity. They are made by two subu nits with an apparent M-r value of 35000 and their optimal pH is 4.5. Inver tase I was eluted from cell walls with ionic strength while invertase II re mained tightly bound to cell walls after this treatment. This invertase was solubilized by enzymatic cell wall degradation (solubilized invertase II). Their K(m)s are 28, 20, 133 and 128 mM for acid soluble invertase, inverta se I, invertase II and solubilized invertase II, respectively. Glucose is a non-competitive inhibitor of invertase activities and fructose produces a two site competitive inhibition with interaction between the sites. Bovine serum albumin produces activation of the acid soluble invertase and inverta se I while a similar inhibition by lectins and endogenous proteinaceous inh ibitor from mature S. tuberosum tubers was found. Invertase II (tightly bou nd to the cell walls) shows a different inhibition pattern. The test fbr re association of the acid soluble invertase or invertase I on cell wall, free of invertase activity, caused the reappearance of all invertase forms with their respective solubilization characteristics and molecular and kinetic properties. The invertase elution pattern, the recovery of cell wall firmly bound invertase and the coincidence in the immunological recognition, sugg est that all three invertases may be originated from the same enzyme. The d ifference in some properties of invertase II and solubilized invertase II f rom the other two enzymes would be a consequence of the enzyme microenviron ment in the cell wall or the result of its wall binding. (C) 1998 Elsevier Science Ltd. All rights reserved.