02355naa a2200289 a 450000100080000000500110000800800410001902400350006010000200009524501460011526000090026150000230027052014660029365000110175965000110177065000130178165000430179465000170183765000150185465300310186965300270190065300220192770000170194970000170196670000170198377300650200021651382024-06-26       1996    bl uuuu     u00u1 u    #d7 a10.1017/s002202990003154x2DOI1 aCOOLBEAR, K. P.  aComparative study of methods for the isolation and purification of bovine kappa-casein and its hydrolysis by chymosin.h[electronic resource]  c1996  aComparative study.  aAbstract: kappa-Casein was purified from a single batch of whole acid casein (kappa-A variant) using different methods in order to compare their merits in producing a purified material with a carbohydrate and phosphate heterogeneity representative of the whole kappa-casein complement in milk. Ion-exchange methods of purification gave products of higher purity than precipitation techniques involving final purification by ethanol fractionation, but all methods resulted in kappa-caseins of apparently similar heterogeneity and chemical composition. The purified kappa-caseins were hydrolysed with chymosin and the derived macropeptides isolated. These were all virtually identical as determined by reversed-phase chromatography and gel electrophoresis. Some observations on chymosin hydrolysis of kappa-casein were made. In addition to formation of the major para-kappa-casein (Glu1-Phe105) and macropeptide (Met106-Val169), chymosin hydrolysis at pH 6.6 also resulted in two minor para-kappa-caseins with N-termini corresponding to Phe18 and Ser33 of kappa-casein. At pH 5.5 and 4.5 para-kappa-casein was rapidly hydrolysed into at least six fragments, one of which had an N-terminus corresponding to Trp76 of kappa-casein. At pH 6.6, 5.5 and 4.5 the kappa-casein macropeptide was stable to chymosin, but at pH 2.3 it was hydrolysed by chymosin into fragments with N-termini corresponding to Met106, Ile125, Ala138, Val139, Thr145 and Glu147 of kappa-casein.  aCasein  aCattle  aChymosin  aHigh performance liquid chromatography  aKappa-casein  aMetabolism  aHydrogen-ion concentration  aIsolation purification  aPeptide fragments1 aELGAR, D. F.1 aCOOLBEAR, T.1 aAYERS, J. S.  tJournal of Dairy Researchgv. 63, n. 1, p. 61-71, Feb. 1996.