DEVELOPMENT OF THE ORNITHINE CYCLE IN RAT-LIVER - ZONATION OF A METABOLIC PATHWAY

Ammonia-fixation in mammalian livers is, via the ornithine cycle and g lutamine synthetase, strictly compartmentalized, occurring in a wide u pstream periportal compartment and in the very last downstream pericen tral hepatocytes, respectively, This conclusion is based on the well-k nown distribution patterns of carbamoyl phosphate synthetase I (CPS) a nd glutamine synthetase in the developing and adult liver, To determin e to what extent the expression patterns of the ornithine cycle enzyme s are coordinated with that of CPS, we investigated the patterns of ex pression of the individual messenger RNAs (mRNAs) of the ornithine cyc le pathway in developing and adult rat liver, Our results show that, w ithin the liver, all mRNAs of the ornithine cycle pathway are zonated, The patterns of expression of the different mRNAs match almost perfec tly, with variations only in the steepness of the gradients of the mRN As, suggesting that, in the rat, common regulatory factors are involve d in the establishment of the zonation pattern.