Light regulation of cGMP metabolism in toad rod outer segments (ROS) deduced from intact photoreceptor and cellfree kinetics

Conference · Fri May 01 04:00:00 EDT 1987 · Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States)

OSTI ID:6372218

Dawis, S M; Graeff, R M; Heyman, R A; Walseth, T F; Butz, E A

The rate of cGMP hydrolysis by phosphodiesterase (PDE) in intact ROS, monitored in dark-adapted isolated toad retina by the rate of /sup 18/O appearance in guanine nucleotide ..cap alpha..-phosphoryls, is 1/360th of that observed in disrupted ROS at a substrate concentration equivalent to the total (cGMP) in ROS. Low to moderate photic stimuli increase this cGMP hydrolytic rate up to 10-fold in intact ROS with little or no change in total (cGMP). G-protein activation determined in intact ROS by the fraction of GDP labeled with /sup 18/O corresponds with light-related increases in cGMP flux. In contrast, relatively high intensities and extended illumination cause attenuation of maximal cGMP hydrolysis with proportionate reductions in total (cGMP). From these observations combined with the effects of activated G-protein on kinetics and cGMP binding of ROS PDE the following model for light-regulation of cGMP metabolism was deduced: cGMP flux in intact ROS is severely restricted in the dark state because approximately 99% of the cGMP is bound to high affinity sites on the non-stimulated form of PDE. This constraint is relieved when activated G-protein converts the cGMP-binding form of PDE to a high K/sub m/ catalytic form. cGMP is then redistributed to a dynamic pool where it is available to PDE catalytic sites and lower affinity allosteric sites. The (cGMP) in the dynamic pool is maintained or further increased or decreased by modulating the activity of an apparently light-sensitive guanylyl cyclase.

• Research Organization: Univ. of Minnesota, Minneapolis
• OSTI ID: 6372218
• Report Number(s): CONF-870644-
• Conference Information: Journal Name: Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States) Journal Volume: 46:6
• Country of Publication: United States
• Language: English

Related Subjects

550501* -- Metabolism-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AMPHIBIANS
ANIMALS
AQUATIC ORGANISMS
BIOCHEMICAL REACTION KINETICS
BODY
BODY AREAS
CYCLASES
ELECTROMAGNETIC RADIATION
ENZYME ACTIVITY
ENZYMES
ESTERASES
EVEN-EVEN NUCLEI
EYES
FACE
FROGS
HEAD
HYDROLASES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGHT NUCLEI
LYASES
METABOLISM
NUCLEI
NUCLEOTIDES
ORGANIC COMPOUNDS
ORGANS
OXYGEN 18
OXYGEN ISOTOPES
PHOSPHODIESTERASES
RADIATIONS
REACTION KINETICS
SENSE ORGANS
STABLE ISOTOPES
TRACER TECHNIQUES
VERTEBRATES
VISIBLE RADIATION