Mode of formation of milk fatty acids from acetate in the goat

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Abstract
Milk fatty acids obtained from a lactating goat after the injn. of CH3 C14O2 Na were resolved into individual acids and their C14 content determined. All the even numbered saturated acids from C2 to C18 and also oleic acid were isolated. Traces of propionic and valeric acids were also identified by paper chromatography. Chemical degradations of acetic, butyric and caproic acids were carried out. Only the carboxyl C of acetic acid contained C14. Butyric acid is synthesized from acetate molecules in such a way that the methyl C of one becomes linked to the carboxyl C of the other. It is inferred that only about 40% of the butyric acid is synthesized from acetate, the other 60% being derived from a non-isotopic C4 compound, possibly beta-hydroxybutyric acid. Caproic acid is synthesized by the elongation of the butyric acid chain at the carboxyl end by the addition of acetate. The metabolic "pools" of the short chain acids (up to C10) in the mammary gland cells appear to be very small. The results are consistent with the view that all the milk fatty acids up to and including palmitic are formed by the stepwise elongation of a shorter acid by the addition of a C2 compound derived from acetate. Stearic and oleic acids might be derived mainly from the blood or from a precursor other than acetate. The possible relationship between the mechanism of fatty acid synthesis in the mammary gland and in other mammalian tissues is discussed.