After catalytic hydrogenation of the unsaturated fatty acids, the branched chain fatty acids of human milk fat were enriched 100-500-fold by urea fractionation. The fatty acid (FA) mixture obtained was qualitatively and quantitatively analysed by a combination of gas chromatograph-mass spectrometer (LKB 9000) using packed columns, thin film and S.C.O.T. capillary columns.
More than 50 single and multi branched acids could be identified, From the distribution of the individual branching points, it is concluded, that two major pathways exist for the biosynthesis of these acids: either by chain elongation of the branched CoA-esters (such as isobutyryI-CoA, ..~-and fl-methylbutyryl-CoA) or by methylation of the double bond of monoenoic acids. The quantitative distribution of the branched acids strongly resembles that found in many micro-organisms.
Hence it is assumed, that a large number of these acids is produced in -or absorbed from-the intestinal tract.
In breast fed infants, human milk exhibits a peculiar enhancement of resistance against a great variety of bacterial and viral infections1). Human milk also protects mice against a lethal dose of Staphylococcus aureus~2).
During the investigation of this phenomenon, it has been found, that the "resistance enhancing factor" is contained in the fatty acid (FA) fraction3).
Therefore a detailed examination of the FA of human milk has been under-taken4-6). The present paper deals with the saturated branched chain FA.
Branched chain FA from mammalian tissues and fluids have repeatedly been described v-12). The occurrence of phytanic acid, phytenic acids, their major degradation products and their role in Refsum's disease (Heredopathia atactica polyneuritiformis) is amply reported4,1a-17). In contrast to the biosynthesis and function of branched chain FA in micro-organisms as ')0) little is known about their origin and biological function in mammalsZ~).