Azuma N, Nara K, Kanno C
Department of Animal Science, Faculty of Agriculture, Utsunomiya University, Japan.
J Dairy Res. 1991 Nov;58(4):421-9. 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.
用肽基精氨酸脱亚氨酶（EC 3.5.3.15）进行酶促修饰，使得αs1-酪蛋白六个精氨酰残基中的五个被转化为瓜氨酰残基，只有N端的精氨酰残基未受影响。通过聚丙烯酰胺凝胶电泳（PAGE）证实了净负电荷的增加。完整的αs1-酪蛋白的等电点从4.46降至脱亚氨型的4.30，同时将酸沉淀起始点从pH 5.17降至pH 4.62。脱亚氨的αs1-酪蛋白在无钙情况下的自缔合较少，且比天然型对钙的敏感性更低，尽管其钙结合能力略有增强。在存在25 mM氯化钙和κ-酪蛋白的情况下，未发生钙诱导的αs1-酪蛋白沉淀，混合物溶液保持透明。αs1-酪蛋白的脱亚氨作用导致其特性发生改变，可能是通过干扰疏水作用和/或氢键相互作用。精氨酰残基的正电荷可能在酪蛋白胶束形成中起重要作用。
