A method for determination of macropeptide by cation-exchange fast protein liquid chromatography and its use for following the action of chymosin in milk

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Abstract
Summary: Cation-exchange chromatography on a Mono S column (Pharmacia) was used to separate macropeptide from whey proteins. Macropeptide was eluted by 0·1 M-NaCl in a 20 mM-KCl–HCl buffer, pH 2. This technique was suitable for quantitative determination of macropeptide in rennet whey and also for following the action of chymosin on κ-casein in skim milk. Precipitation at pH 4·6 was used to remove residual caseins and to keep macropeptide in solution. In comparison with other methods for determining macropeptide, the present one eliminates the need for pretreatment of samples with trichloroacetic acid (TCA) and allows the recovery of all the macropeptide. Quantitative determination of macropeptide in the 8% TCA-soluble fraction by cation-exchange chromatography showed that only 50–75% of the macropeptide was recovered. This chromatographic technique could also be applied for isolating and producing whole macropeptide on a preparative scale.