Linked Life Data

6255064

Source:http://linkedlifedata.com/resource/pubmed/id/6255064

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
5
pubmed:dateCreated
1981-2-19
pubmed:abstractText
The light-activated cyclic GMP phosphodiesterase (PDE) of frog photoreceptor membranes has been assayed in isolated outer segments suspended in a low-calcium Ringer's solution. Activation occurs over a range of light intensity that also causes a decrease in the permeability, cyclic GMP levels, and GTP levels of isolated outer segments. At intermediate intensities, PDE activity assumes constant intermediate values determined by the rate of rhodopsin bleaching. Washing causes an increase in maximal enzyme activity. Increasing light intensity from darkness to a level bleaching 5 x 10(3) rhodopsin molecules per outer segment per second shifts the apparent Michaelis constant (Km) from 100 to 900 microM. Maximum enzyme velocity increases at least 10-fold. The component that normally regulates this light-induced increase in the Km of PDE is removed by the customary sucrose flotation procedures. The presence of 10(-3) M Ca++ increases the light sensitivity of PDE, and maximal activation is caused by illumination bleaching only 5 x 10(2) rhodopsin molecules per outer segment per second. Calcium acts by increasing enzyme velocity while having little influence on Km. The effect of calcium appears to require a labile component, sensitive to aging of the outer segment preparation. The decrease in the light sensitivity of PDE that can be observed upon lowering the calcium concentration may be related to the desensitization of the permeability change mechanism that occurs during light adaptation of rod photoreceptors.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Nov
pubmed:issn
0022-1295
pubmed:author
pubmed:issnType
Print
pubmed:volume
76
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
631-45
pubmed:dateRevised
2008-11-21
pubmed:meshHeading
pubmed:year
1980
pubmed:articleTitle
Control of the cyclic GMP phosphodiesterase of frog photoreceptor membranes.
pubmed:publicationType
Journal Article, In Vitro, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't