Action of protein-glutaminase on alpha-lactalbumin in the native and molten globule states.
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-lactablumin revealed that the stability of the tertiary structure of alpha-lactablumin 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.
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Laboratory of Quality Analysis and Assessment, Division of Agronomy and Horticultural Science, Graduate School of Agriculture, Kyoto University, Gokasho, Uji, Kyoto 611-0011 Japan.
Matsumura
Y
Y
Yamaguchi
S
S
Mori
T
T
D000595:Amino Acid Sequence; D000641:Ammonia / Q000032:analysis; D002942:Circular Dichroism; D004220:Disulfides / Q000737:chemistry; D005417:Flavobacterium / Q000201:enzymology; D007700:Kinetics; D007768:Lactalbumin / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D011489:Protein Denaturation; D012697:Serine Endopeptidases / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D011503:Transglutaminases / Q000378:metabolism*
D004220:Disulfides; D010446:Peptide Fragments; D000641:Ammonia; D007768:Lactalbumin; D011503:Transglutaminases; D012697:Serine Endopeptidases; C028344:glutamyl endopeptidase