Abstract
The enzymic assay for the A protein of lactose synthetase (galactosyl transferase) was carefully evaluated using bovine α-lactalbumin to assay for purified bovine A protein and the A protein in rat mammary homogenates. With purified bovine proteins, the maximum activity was found with 200 μg α-LA/ml with higher levels being inhibitory. With the rat A protein in mammary homogenates, 1 mg bovine α-LA/ml gave the maximum rate. The assay parameters for maximum lactose synthetase and N-acetyllactosamine formation were similar. The enzymic assay for the B protein (α-lactalbumin) of lactose synthetase has been thoroughly investigated using purified bovine α-LA and α-LA present in rat mammary gland homogenates. A correction was necessary for the endogenous lactose synthetase activity of the A protein alone which was dependent on the glucose concentration in the assay. A standard curve of bovine α-LA was necessary for each set of assays since there was variation in the properties of different preparations of the A protein. Under the assay conditions described the amount of α-lactalbumin in the assay (0.02–1.0 μg) per milliliter was quantitatively related to the amount of standard bovine α-lactalbumin.
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