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Membranes of Mammary Gland: I. Bovine Mammary Mitochondria

Department of Animal Sciences, Purdue University, Lafayette, Indiana 47907

ABSTRACT

Purified mitochondrial fractions were isolated from lactating bovine mammary gland and were characterized by electron microscopy and assayed for electron transport ability, cytochrome content, and enzymes characteristic of other cellular membranes. The mitochondria contained 0.35 mg of lipid per milligram of protein. The major constituents of the phospholipid fraction, which accounted for 85% of the total lipids, were choline and ethanolamine glycerophosphatides and diphosphatidyl glycerol. Significant amounts of coenzyme Q, cholesterol, and free fatty acids also were present. The fatty acids of mitochondrial lipids were highly unsaturated. Oleic and linoleic acids were the major unsaturated acyl residues encountered; only small amounts of unsaturated acids with chain lengths greater than 18 carbon atoms were detected. Of the individual phospholipids, diphosphatidyl glycerol contained the most and sphingomyelin the least unsaturated fatty acids. Electrophoretically, both qualitative and quantitative differences in protein were observed comparing mitochondria from bovine heart and mammary gland.

Compared with literature values, mammary mitochondria contain lipid, coenzyme Q, cytochromes a₃ + a, and NADH-cytochrome c reductase in amounts near those of bovine heart mitochondria. Mitochondria from bovine liver and kidney contain lesser amounts of these constituents. Thus, bovine mammary mitochondria resemble those of heart in composition and electron transport ability.