Abstract
Tomato (Lycopersicon esculentum Mill) fruit tissue was found to contain two isoforms of a-d-mannosidase (EC. 3.2.1.24), which were purified by ion-exchange chromatography on DEAE sephadex A-50 followed by gel filtration on sephadex G-100. The two isoforms were named isoform I and II (minor and major forms, respectively) which differed in their abundance, their elution profile on both ion-exchange and gel filtration column chromatography. Isoforms I and II showed 6 and 24% of the total activity, respectively. Both the isoforms had an acid pH optimum (4.5) and were thermally stable at 65° for up to 15 min. Isoform I showed a broad temp optimum between 55 and 65° whereas isoform II had an optimal activity at 65°. The Km values of isoforms I and II for p-nitrophenyl-a-d-mannopyranoside were 1.11 and 1.05 mM, respectively. The activity of isoform I was inhibited by Hg2 (1 mM) whereas isoform II was inhibited by Cu2 (0.1 mM) and Hg2 (1 mM). Both the isoforms were free of other glycosidases. Purified isoform II had a SDS Mr of ca. 38,000.
Published Version
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