Chromium(III). beta. ,. gamma. -bidentate guanine nucleotide complexes as probes of the GTP-activated cGMP cascade of retinal rod outer segments

Journal Article · Tue Oct 18 00:00:00 EDT 1988 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00421a034· OSTI ID:7189674

Frey, S E; Hingorani, V N; Su-Tsai, Saiumei; Ho, Yeekin ^[1]

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1. Univ. of Illinois, Chicago (USA)

The exchange-inert Cr(III) {beta},{gamma}-bidentate guanine nucleotide complexes Cr(III)GTP and Cr(III)Gpp(NH)p were used to probe the role of transducin in activating the retinal cGMP cascade. The Cr(III) nucleotide complexes were found to have lower binding affinity for transducin as compared to the Mg{sup 2+} complexes. However, the rate of hydrolysis of the transducin-bound Cr(III)GTP was similar to that of Mg(II)GTP. Cr(III)Gpp(NH)p activated the cGMP phosphodiesterase of photolyzed rod outer segment membranes up to 75% of the Mg(II)Gpp(NH)p level but lacked the ability to dissociate the transducin subunits from the rod outer segment membrane. This result implies that the activation of the phosphodiesterase by transducin-GTP complex is a membrane-associated event and the formation of a soluble complex of transducin-GTP with the inhibitory peptide of the phosphodiesterase may not be an obligatory step. Both the {Delta} and {Lambda} screw sense stereoisomers of Cr(III)Gpp(NH)p were capable of activating the cGMP cascade with no apparent stereoselectivity. The nature of the interaction of the metal ion and GTP at the nucleotide-binding site of transducin is discussed together with the results from previous studies using the phosphorothioate GTP analogues and is compared to the site found in homologous GTP-binding proteins such as elongation factor Tu. The implications of the observed results on the molecular mechanism of visual signal transduction are discussed.

• OSTI ID: 7189674
• Journal Information: Biochemistry; (USA), Journal Name: Biochemistry; (USA) Vol. 27:21; ISSN 0006-2960; ISSN BICHA
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BODY
BODY AREAS
CATTLE
CHEMICAL ACTIVATION
CHEMICAL REACTIONS
CHROMATOGRAPHY
CHROMIUM COMPLEXES
COMPLEXES
DAYS LIVING RADIOISOTOPES
DECOMPOSITION
DICHROISM
DOMESTIC ANIMALS
ENZYMES
ESTERASES
EYES
FACE
HEAD
HYDROLASES
HYDROLYSIS
ISOTOPES
LIGHT NUCLEI
LIQUID COLUMN CHROMATOGRAPHY
LYSIS
MAMMALS
NUCLEI
NUCLEOTIDES
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANS
PHOSPHODIESTERASES
PHOSPHORUS 32
PHOSPHORUS ISOTOPES
RADIOISOTOPES
RETINA
RUMINANTS
SENSE ORGANS
SEPARATION PROCESSES
SOLVOLYSIS
STEREOCHEMISTRY
TRANSITION ELEMENT COMPLEXES
VERTEBRATES