Multiple forms of β-galactosidase from mango (Mangifera indica L Alphonso) fruit pulp

Mango (Mangifera indica L cv Alphonso) was found to contain three isoforms (I, II and III) of beta-galactosidase which, upon purification on Sephadex G-200, had relative abundances of 44, 38 and 18%, respectively. The total specific activity increased from 20 to 72 7 mu mol 1(-1) upon purification, representing a similar to 36-fold increase with a recovery of 0.28 U U-1. The optimal pH for activity and stability were in the ranges 3.6-4.3 and 4-6.2, respectively. The optimal temperature for beta-galactosidase activity was between 42 and 47 degrees C with T-m in the range 45-51 degrees C. The K-m for pNP-beta-galactopyranoside was 0.98, 1.11 and 0.95 nM, and V-max was 0.56, 0.53 and 0.35 gmol pNP min(-1), respectively for isoforms I, II and III. Hg2+ caused strong inhibition, whereas galacturonic acid, galactose, xylose, fucose and mannose slightly inhibited the activity of beta-galactosidase isoforms. The apparent molecular weights by GPC were 78, 58 and 91 kDa for isoforms I, II and III, respectively. The ability of these isoforms to degrade the endogenous substrate (arabinogalactan) possibly suggests a role in pectin dissolution during tissue softening/fruit ripening. (c) 2004 Society of Chemical Industry.