Reciprocal effects of an inhibitory factor on catalytic activity and noncatalytic cGMP binding sites of rod phosphodiesterase. [Rana catesbiana]
In illuminated rod outer segment membranes, GTP and guanosine 5'-(..beta..,..gamma..-imido)triphosphate (p(NH)ppG) have reciprocal effects on cGMP phosphodiesterase (PDEase; 3':5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) activity and cGMP binding to noncatalytic sites on that enzyme. Two micromolar p(NH)ppG increased PDEase activity more than 2-fold while inhibiting cGMP binding more than 40%. Reduction of noncatalytic cGMP binding, which followed addition of p(NH)ppG, was not a result of PDEase activation. Both effects of p(NH)ppG were completely dependent on the presence of bleached rhodopsin. A heat-stable factor has been found to inhibit PDEase activity and also to stimulate cGMP binding to noncatalytic cGMP binding sites. Addition of p(NH)ppG reversed the effects of this factor on both PDEase activity and cGMP binding. During purification of this material, the activity peaks for both PDEase inhibition and activation of noncatalytic cGMP binding comigrated on both Blue Sepharose CL-6B column chromatography and sucrose density gradients centrifugation, suggesting that the same factor could be responsible for both inhibition of PDEase activity and enhancement of noncatalytic cGMP binding. Limited tryptic proteolysis of PDEase, which markedly reduced cGMP binding to the noncatalytic sites, and experiments using highly purified cAMP (free of cGMP) as substrate for PDEase showed that the binding of cGMP to noncatalytic sites was not required for the heat-stable inhibitory factor to inhibit PDEase activity. We discuss possible relationships between the regulation of PDEase and the binding of cGMP to noncatalytic sites.
- Research Organization:
- Los Alamos National Lab., NM
- OSTI ID:
- 7090361
- Journal Information:
- Proc. Natl. Acad. Sci. U.S.A.; (United States), Vol. 79:12
- Country of Publication:
- United States
- Language:
- English
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CATALYSIS
INHIBITION
GUANOSINE
CHEMICAL BONDS
PHOSPHODIESTERASES
ENZYME ACTIVITY
RETINA
PHOTOCHEMICAL REACTIONS
BIOCHEMICAL REACTION KINETICS
CELL MEMBRANES
FROGS
AMPHIBIANS
ANIMALS
AQUATIC ORGANISMS
BODY
BODY AREAS
CELL CONSTITUENTS
CHEMICAL REACTIONS
ENZYMES
ESTERASES
EYES
FACE
HEAD
HETEROCYCLIC COMPOUNDS
HYDROLASES
KINETICS
MEMBRANES
NUCLEOSIDES
NUCLEOTIDES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANS
PURINES
REACTION KINETICS
RIBOSIDES
SENSE ORGANS
VERTEBRATES
550200* - Biochemistry