Catalytic characterization of phytase (myo-inositolhexakisphosphate phosphohydrolase) from Aspergillus niger van Teighem:Glycosylation pattern,kinetics and molecular properties

摘要

A phytase with a high specific activity from Aspergillus niger van Teighem was purified to near homogeneity and characterized in terms of different catalytic properties.The N-terminal sequence of purified phytase was determined to be FYYGAALPQS.The purified phytase was a glycosylated protein as judged by positive PAS staining with pI of 3.8 as estimated by two-dimensional gel electrophoresis.The kinetic studies revealed that the enzyme was competitively inhibited by myo-inositolhexasulphate (MIHS),a structural analogue of phytic acid,with apparent K_i of 0.05 mM.The K_m of the phytase increased from 0.625 to 1.898 mM in the presence MIHS with 50% inhibition of phytase activity at 100 mu M MIHS.The enzyme was significantly inhibited by inorganic phosphorus in uncompetitive manner (K_i=0.16 mM) with 50% inhibition of phytase activity at 0.2 mM P_i.This phytase protein was approx.three-fold more sensitive to MIHS inhibition than inorganic phosphorus.