Enzymic modification of alpha s1-casein with peptidylarginine deiminase: preparation of less acid-coagulable and less calcium-sensitive casein.
Enzymic modification with peptidylarginine deiminase (EC 3.5.3.15) enabled five out of six arginyl residues in alpha s1-casein to be converted to citrullyl residues, only the N-terminal arginyl residue remaining unaffected. An increase in the net negative charge was confirmed by PAGE. The isoelectric point was decreased from 4.46 for the intact alpha s1-casein to 4.30 for the deiminated type, while simultaneously lowering the acid-precipitation starting point from pH 5.17 to pH 4.62. The deiminated alpha s1-casein self-associated less in the absence of Ca and was less Ca-sensitive than the native type, although its Ca-binding ability was slightly enhanced. In the presence of 25 mM-CaCl2 and kappa-casein, Ca-induced precipitation of alpha s1-casein did not occur, the solution of the mixture remaining transparent. Deimination of alpha s1-casein resulted in altering its characteristics, possibly by interfering with interactions through hydrophobicity and/or hydrogen bonding. The positive charge of the arginyl residues might play an important role in casein micelle formation.
Azuma
N
N
Department of Animal Science, Faculty of Agriculture, Utsunomiya University, Japan.
Nara
K
K
Kanno
C
C
D000596:Amino Acids / Q000032:analysis / Q000737:chemistry; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002364:Caseins / Q000737:chemistry / Q000378:metabolism*; D002417:Cattle; D011232:Chemical Precipitation; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006863:Hydrogen-Ion Concentration; D006867:Hydrolases / Q000378:metabolism*; D007526:Isoelectric Point; D008892:Milk / Q000378:metabolism*; D010449:Peptide Mapping; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases
D000596:Amino Acids; D002364:Caseins; D006867:Hydrolases; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases; D002118:Calcium