Incorporation of amino acids by isolated submitochondrial fractions of lactating goat mammary gland in vitro.

Incorporation of amino acids by mitochondria and its subfractions from mammary gland of the goat during lactation was studied in vitro. Assessment of distribution of radioactivity incorporated by intact mitochondria into its subfractions revealed maximum specific activity in the inner membrane. During lactation the inner membrane of mitochondria exhibited further stimulation in such incorporation. Matrix was the next active fraction whereas outer membrane and peripheral space had negligible radioactivity. In isolated submitochondrial fractions from mammary gland incubated with radioactive amino acids under similar conditions of assay, the inner membrane was the most potent subfraction in incorporation. In mammary tissue during lactation this fraction was the most active site. The relative sequence of the subfractions appeared to remain unaltered in lactation and was in the order of inner membrane greater than matrix greater than outer membrane greater than peripheral space. The ratio of specific activity in inner to outer membrane appears to increase significantly during lactation.