title: Characterization of gamma-glutamyl transpeptidase from the Rathke's gland secretions of Kemp's ridley sea turtles (Lepidochelys kempi).
abstract: The secretion produced by Rathke's glands of Kemp's ridley sea turtles (Lepidochelys kempi) contains the enzyme gamma-glutamyl transpeptidase. The approximately 200 kDa enzyme contains two different subunits, alpha (54 kDa) and beta (21 kDa), in an unknown stoichiometry. The enzyme transfers gamma-Glu from a number of different donors, such as glutamine, glutathione, S-Me-glutathione, N epsilon(gamma-Glu)-Lys, gamma-Glu-Ala, and other gamma-glutamyl amino acids, either to water or to a variety of acceptor substrates. It appears that a free alpha-amino group is the preferred acceptor. The enzyme is not inhibited by typical sulfhydryl reagents such as N-ethyl-maleimide, p-(chloro)mercuri-benzoate or 5,5'-dithio-bis-(2-nitrobenzoate) or by the active Ser reagent tosyl fluoride. Maleate stimulates the activity of the enzyme, and in the presence of 100 mM maleate 2 mM tosyl fluoride becomes an inactivator of the enzyme. The catalytic and molecular properties of the turtle gamma-glutamyl transpeptidase are similar to those established for mammalian gamma-glutamyl transpeptidase. Neither the physiological role of the enzyme nor the biological function of the secretion in which it occurs is understood at this time.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston 77225, USA.
authors.forename: R G
authors.initials: RG
authors.lastname: Krishna
authors.forename: C C
authors.initials: CC
authors.lastname: Chin
authors.forename: P J
authors.initials: PJ
authors.lastname: Weldon
authors.forename: F
authors.initials: F
authors.lastname: Wold
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004789:Enzyme Activation; D008969:Molecular Sequence Data; D013379:Substrate Specificity; D014426:Turtles / Q000378:metabolism*; D005723:gamma-Glutamyltransferase / Q000737:chemistry* / Q000302:isolation & purification
chemical_list: D005723:gamma-Glutamyltransferase