EVIDENCE THAT LIVER-MICROSOMES OF HUMAN NEONATES DESATURATE ESSENTIALFATTY-ACIDS

DELTA6- and DELTA5-Desaturation of essential fatty acids of n - 6 and n - 3 series are required for the biosynthesis of polyunsaturated fatt y acids (PUFAs), which are precursors of eicosanoids and constituents of membrane phospholipids. This pathway could be of special importance during the perinatal period, when PUFAs accretion in the central nerv ous system is very active. However, experimental evidence of DELTA6- a nd DELTA5-desaturase activities in man is very scarce, and no data are available for newborns. We report the DELTA6- and DELTA5-desaturase a ctivities detected in human liver microsomes from three neonates who d ied from associated malformations. Radiochemical assays of DELTA6- and DELTA5-desaturase activities performed with reverse phase HPLC analys is of the products in the n - 6 series ranged from 4.8-13.6 to 3.2-16. 4 pmol substrate converted . min-1 . mg - 1 microsomal proteins, respe ctively. In the n - 3 series DELTA 6-desaturase activity ranged from 5 .3 to 12.8 pmol . min- 1 - mg-1. The relationships between enzyme acti vities and substrate concentrations suggest excess substrate inhibitio n for n - 6 and not for n - 3 fatty acids. These results demonstrate s ignificant DELTA6- and DELTA5-desaturase activities in human liver of neonates, but this activity was lower than previously reported in adul t humans and in mammals, especially rodents.