Characterization of gamma-glutamyl transpeptidase from the Rathke's gland secretions of Kemp's ridley sea turtles (Lepidochelys kempi).
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.
Krishna
R G
RG
Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston 77225, USA.
Chin
C C
CC
Weldon
P J
PJ
Wold
F
F
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
D005723:gamma-Glutamyltransferase