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Purification and partial characterization of xyloglucan-hydrolyzing enzymes from watermelon placental tissue

Karakurt, Yasar, Huber, Donald J.
Journal of the science of food and agriculture 2009 v.89 no.4 pp. 645-652
Citrullus lanatus, watermelons, fruits (plant anatomy), O-glycoside hydrolases, purification, enzyme activity, xyloglucans, enzymatic hydrolysis, molecular weight
BACKGROUND: Watermelon (Citrullus lanatus (Thunb.) Matsum & Nakai) fruit matrix glycans are comprised largely of xyloglucans (XGs). As in other fruits, these polymers show significant molecular mass downshifts during ripening. In the present study, we describe the purification and characteristics of a number of xyloglucanases (XGases) from the placental tissue of ripe watermelon. XGases were extracted from watermelon fruit placental tissue and purified by sequential ion-exchange, gel-permeation and concanavalin A chromatography.RESULTS: Five XGases (P1S2, P2S2, P3S1, P3S2, P3S3) were recovered with molecular masses ranging from 30.5 to 77.5 kDa on SDS-PAGE. All XGases showed maximum activity at pH 5-5.5 and 35-40 °C against tamarind seed XG and were also active against XG-rich matrix glycans from watermelon fruit. The enzymes were strongly inhibited by mercury and hydrolyzed XG without generation of oligomers or monomers. P3S3 had the highest activity against XG. The purified enzymes were active toward carboxymethylcellulose, indicating that they were not XG specific.CONCLUSION: The pattern of molecular mass downshifts during XG hydrolysis by the purified XGases and the absence of monomeric and oligomeric products are consistent with endo-type catalysis for the XGases and with a role for these enzymes in the degradation of cell wall XG during ethylene-induced watersoaking of watermelon fruit placental tissues.