Catalytic properties of wheat phytase that favorably degrades long-chain inorganic polyphosphate.

Abstract

ObjectiveThis study was conducted to determine catalytic properties of wheat phytase with exopolyphosphatase activity toward medium-chain and long-chain inorganic polyphosphate (polyP) substrates for comparative purpose.MethodsExopolyphosphatase assay of wheat phytase toward polyP75 (medium-chain polyP with average 75 phosphate residues) and polyP1150 (long-chain polyP with average 1150 phosphate residues) was performed at pH 5.2 and pH 7.5. Its activity toward these substrates was investigated in the presence of Mg2+, Ni2+, Co2+, Mn2+, or ethylenediaminetetraacetic acid (EDTA). Michaelis constant (Km) and maximum reaction velocity (Vmax) were determined from Lineweaver-Burk plot with polyP75 or polyP1150. Monophosphate esterase activity toward p-nitrophenyl phosphate (pNPP) was assayed in the presence of polyP75 or polyP1150.ResultsWheat phytase dephosphorylated polyP75 and polyP1150 at pH 7.5 more effectively than that at pH 5.2. Its exopolyphosphatase activity toward polyP75 at pH 5.2 was 1.4-fold higher than that toward polyP1150 whereas its activity toward polyP75 at pH 7.5 was 1.4-fold lower than that toward polyP1150. Regarding enzyme kinetics, Km for polyP75 was 1.4-fold lower than that for polyP1150 while Vmax for polyP1150 was 2-fold higher than that for polyP75. The presence of Mg2+, Ni2+, Co2+, Mn2+, or EDTA (1 or 5 mM) exhibited no inhibitory effect on its activity toward polyP75. Its activity toward polyP1150 was inhibited by 1 mM of Ni2+ or Co2+ and 5 mM of Ni2+, Co2+, or Mg2+. Ni2+ inhibited its activity toward polyP1150 the most strongly among tested additives. Both polyP75 and polyP1150 inhibited the monophosphate esterase activity of wheat phytase toward pNPP in a dose-dependent manner.ConclusionWheat phytase with an unexpected exopolyphosphatase activity has potential as a therapeutic tool and a next-generational feed additive for controlling long-chain polyP-induced inappropriate inflammation from Campylobacter jejuni and Salmonella typhimurium infection in public health and animal husbandry.