Enzymic modification of alpha s1-casein with peptidylarginine deiminase: preparation of less acid-coagulable and less calcium-sensitive casein

• Published in: Journal of dairy research Vol. 58; no. 4; p. 421
• Main Authors: Azuma, N, Nara, K, Kanno, C
• Format: Journal Article
• Language: English
• Published: England 01.11.1991
• Subjects: Amino Acids - analysis; Amino Acids - chemistry; Animals; Calcium - metabolism; Caseins - chemistry; Caseins - metabolism; Cattle; Chemical Precipitation; Chromatography, High Pressure Liquid; Electrophoresis, Polyacrylamide Gel; Female; Hydrogen-Ion Concentration; Hydrolases - metabolism; Isoelectric Point; Milk - metabolism; Peptide Mapping; Protein-Arginine Deiminases
• ISSN: 0022-0299
• DOI: 10.1017/S0022029900030028

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.