Characterisation of alpha-amylase and polygalacturonase from Lygus spp. (Heteroptera: Miridae)

Abstract

Polygalacturonase and α-amylase from the salivary glands of Lygus lineolaris and of L. hesperus (Heteroptera: Miridae) were optimally active at acid pH and at 40°C, and were activated by chloride ions. The rates of thermal inactivation of both enzymes followed apparent first-order reaction kinetics, from which apparent thermodynamic variables ( E a, ΔH ‡ , ΔG ‡ and ΔS ‡ ) were calculated. For both enzymes, after exposure to 60–100°C, a biphasic system was demonstrated for their thermal inactivation. Both α-amylases were more active towards gelatinised legume starches than towards soluble starch. The effect of substrate concentration upon the enzyme activities demonstrated higher maximum reaction velocities for the two enzymes from L. lineolaris, and K m V max ratios of 0·31-0·33 for α-amylase and 0·04-0·05 for polygalacturonase. The results from this study indicated the potential abilities of the two enzymes to attack pectic substances and starch in food crops and hence to have a possible potential application in polymer modification in food technology.