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Effects of enzymatic deamidation by protein-glutaminase on structure and functional properties of alpha-zein

Yong, H.Y., Yamaguchi, S., Gu, Y.S., Mori, T., Matsumura, Y.
Journal of agricultural and food chemistry 2004 v.52 no.23 pp. 7094-7100
corn, zein, enzymatic treatment, glutaminase, Chryseobacterium proteolyticum, enzyme activity, functional properties, protein secondary structure, food biotechnology, emulsifying properties, solubility, antioxidant activity, protein aggregates
The performance of novel protein-glutaminase (PG) purified from Chryseobacterium proteolyticum on alpha-zein was investigated. Highly insoluble alpha-zein was able to be deamidated to the extent of deamidation degree 62% by using 50 mM potassium phosphate (pH 8) containing 11.7% ethanol, at 40 degrees C for 137 h. Analysis by sodium dodecyl sulfate polyacrylamide-gel electrophoresis showed that deamidated and non-deamidated zeins have different mobilities. Results of circular dichroism spectra revealed the decline in alpha-helix contents of alpha-zein by deamidation. Besides, Fourier transform infrared spectroscopy analysis demonstrated alterations in the secondary structure of alpha-zein by deamidation. The assignment of the amide I region showed a remarkable decrease in antiparallel intermolecular beta-sheets (around 1690 cm(-1)) as an indication of the weakening aggregation ability of the deamidated molecules. Solubility and emulsification properties of alpha-zein, particularly at pH 7, were remarkably improved after the deamidation by PG. Gas chromatography and peroxide value studies pointed out that deamidated alpha-zein in powder form exhibited an inferior antioxidative property as compared with the non-deamidated one.