Glutamine Synthetase and Glutamyltransferase in Developing Chick and Rat Tissues

Abstract

Concomitant determination of γ-glutamine-hydroxylamine-glutamyltrans-ferase (GT) and γ-glutamyl hydroxamate synthetase (GS) activities in chick retina, brain and liver between the 13th day of incubation and a day after hatching showed that while both activities increased late in incubation, in neural tissues their rises were not simultaneous throughout development; in liver both activities were already high on the 14th day of incubation and changed in parallel thereafter. GS and GT activities could be evoked prematurely in all three tissues by cortisol, but GT activity showed higher responses to the hormone. GT and GS were separable by differential solubilization in chick liver but not in retina of chick or rat. The wide spread of the ratios of GT:GS activities in homogenates of a number of chick and rat tissues (1:1 to 73:1) indicates that the GS reaction is not catalyzed by the same protein that catalyzes the GT reactions. Relative amounts of GT(T) (free of GS activity) and of variants of GS (with different competences to catalyze the GT reaction) may govern the changes between the two activities during development and their distribution among different adult tissues in chick and rat.

Amino Acid Metabolizing Enzymes in Rat Submaxillary Gland, Normal or Neoplastic, and in Pancreas

“…The varying ratios between glutamyl transferase and glutamine synthe tase activities (ranging from 45 in liver to 2.3 in pancreas), observed pre viously in other mammalian and avian tissues [9,13], suggest that pancreas, like rat muscle and heart, contains essentially only glutamine synthetase II with its associated low glutamyl transferase (GT(S)) activity [13] while sub maxillary gland, like rat liver and brain, contains both glutamine synthetase (with GT(S) activity) and glutamyl transferase [12].…”

Developmental Formation and Cortisol Regulation of Gamma-Glutamyl Transpeptidase in Brain and Spinal Cord of Chick Embryo

“…Relatively high levels of GGT activity were estimated in postnatal brain or its different regions [1,11,20,23], However, it is considered that GGT may play a more significant role in amino acid transport in the brain of the fetus than in the adult [15]. As no requirement for monovalent cations was found when GGT activity was studied with gluta thione as the gamma-glutamyl donor [28], the functional role of such a transport system might be more evident during the period of development of the chick embryo brain when the Na+ gradient across membranes of chick nerve cells is not yet established [25], Cortisol has been found to regulate the synthesis of many tissue enzymes [6] including Na^-KT-ATPase [26], gamma-glutamine hydroxylamine glutamyltransferase and gammaglutamyl hydroxamate synthetase [7,18] in the brain of the developing chick embryo. A study of the steroidal regulation of enzyme activities in chick embryo brain offers an opportunity to judge their role in physiological functions dur ing brain development.…”