Alkaline phosphatase was partially purified from human milk and its antigenic, functional and structural properties were characterized. By immunochemical and enzymic criteria, the enzyme resembled the alkaline phosphatase isoenzyme found in human liver. Two-dimensional electrophoretic analysis showed that the milk enzyme differed from the liver both in subunit molecular weight and in isoelectric point. These differences were shown to result from variation in sialic acid content.

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