Tissue distribution of enzymes of arginine biosynthesis in terrestrial snails

1. The levels of activity for ornithine carbamoyltransferase (E.C. 2.1.3.3), argininosuccinate synthetase (E.C. 6.3.4.5) and argininosuccinate lyase (E.C. 4.3.2.1) were determined in various tissues of the land snails Otala lactea and Helix aspersa. The tissues examined were of endodermal, mesodermal and ectodermal origins. All tissues possessed activities of these three enzymes. 2. The levels of the three enzymes were relatively uniform from one tissue to the other with the exception of blood in which only low levels of activity were found. The lack of localization of these enzymes in any one tissue in the snails is in contrast to higher vertebrates where high levels of the arginine pathway enzymes are localized in one or very few tissues. 3. The tissue distribution of the enzymes of arginine biosynthesis in O. lactea and H. aspersa is consistent with previous studies in which it has been shown that the protein arginine in each tissue is labelled following the injection of [¹⁴C]bicarbonate into whole snails. The apparent capacity of each tissue to synthesize arginine may reflect the relative lack of differentiation of the tissues with respect to the arginine pathway in comparison to that found in mammals.