THE ACTION OF ENZYMES ON HUMAN α-LIPOPROTEIN

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Abstract
Gentle extraction with ether removed 31% of the total sterol but no phospholipid from human [alpha]-lipoprotein. After digestion with chymotrypsin, 65% of the nitrogen was rendered trichloroacetic acid-soluble. Ether extracts then contained 44% of the sterol and 23% of the phospholipid. Trypsin breaks down the protein to the same extent as chymotrypsin but has more effect on lipid binding, 65% of the sterol and 53% of the phospholipid appearing in the ether extracts. There was no preferential extraction of either esterified or unesterified sterol from intact or trypsin-digested [alpha]-lipoprotein. Phospholipase D liberated 88% of the choline present in the lipoprotein and, after such treatment, ether extracts contained 79% of the sterol and 51% of the phospholipid. Paper electro-phoresis of trypsin-digested a-lipoprotein revealed no protein-staining zones. Lipid was spread in a wide zone between the origin and the normal [alpha]2-globulin position.