Comparative properties of microsomes from cow's milk and from mammary gland. 2. Chemical composition

Abstract
Several methods for estimation of the nucleic acid content of cytoplasmic particles from animal tissues were investigated. A procedure is described which gave satisfactory results on the basis of agreement between estimates based on absorption at 260 m[mu] and organic phosphorus content. The chemical composition of a preparation of disrupted sarcosomes from pig heart was determined. Microsomes from rat liver and from mammary gland of the lactating cow contained relatively high proportions of phospholipid and of nucleic acids, whereas microsomes from cow''s milk contained much less lipid and considerably less nucleic acid. Incubation of mammary-gland microsomes in milk serum caused some loss of lipid and considerable loss of nucleic acid, so that the product had a composition closely resembling that of microsomes from milk. The significance of these results in relation to the origin of milk microsomes is discussed.