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Action of protein-glutaminase on alpha-lactalbumin in the native and molten globule states

Gu, Y.S., Matsumura, Y., Mori, T.
Journal of agricultural and food chemistry 2001 v.49 no.12 pp. 5999-6005
molecular conformation, enzyme activity, glutaminase, bacteria, Chryseobacterium proteolyticum, protein tertiary structure, lactalbumin
The action of a novel protein-glutaminase from microorganisms on alpha-lactalbumin was investigated. When alpha-lactalbumin in the native state was incubated with protein-glutaminase, the deamidation proceeded gradually, i.e., the deamidation degree increased to 20% and 55% after 4 and 24 h, respectively. The transformation of alpha-lactalbumin from the native state to the molten globule state caused an increase in the rate of the enzyme-catalyzed deamidation, particularly in the early stage. The deamidation degree for the molten globule state reached 61% after 4 h, followed by a gradual increase to 66% after 24 h. CD spectral analyses of deamidated alpha-lactalbumin revealed that the stability of the tertiary structure of alpha-lactalbumin was closely related to the degree of deamidation, whereas the secondary structure was not affected by deamidation. Glutamine residues in alpha-lactalbumin to be modified by protein-glutaminase were identified as Gln[39], [43], [54], and [65]. Conformational characteristics of the amino acid sequence around these glutamine residues are discussed.