Selective extraction of alkaline phosphatase and 5'-nucleotidase from milk fat globule membranes by a single phase n-butanol procedure.

A single phase extraction procedure employing 8% (v/v) n-butanol at room temperature extracted over 90% of alkaline phosphatase activity and over 60% of 5'-nucleotidase activity from bovine milk fat globule membranes (MFGM). For 5'-nucleotidase, higher n-butanol concentrations lead to loss of activity, while lower concentrations were ineffective in extracting the enzyme. When extractions were performed at 0 degrees C, similar yields were obtained for alkaline phosphatase extraction with 8% (v/v) n-butanol, but 5'-nucleotidase extraction required 10% (v/v) n-butanol for similar yields. However, 5'-nucleotidase was less susceptible to denaturation during extraction at 0 degrees C. The Km values and substrate specificities for both alkaline phosphatase and 5'-nucleotidase were unchanged by extraction with 8% (v/v) n-butanol. The 8% (v/v) n-butanol extraction procedure provides a 3-fold purification step, and an enzyme preparation suitable for further purification.