ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract— Cyclic 3′,5′-AMP (cAMP) and cyclic 3′,5′–GMP (cGMP) phosphodiesterase activities were found in human cerebrospinal fluid (CSF) using low substrate concentration (0.4μM). More rapid hydrolysis of cGMP than that of cAMP was observed in human CSF. However, cGMP hydrolytic activity of CSF was very much lower (0.3 pmol/min/ml CSF) than that of human cerebral cortex (33.7 nmol/min/g wet cortex). The pH optimum was found to be 8.0 (cGMP phosphodiesterase) and 7.5 (cAMP phosphodiesterase). The maximum stimulation of both cAMP and cGMP phosphodiesterase was achieved at 4 mM-MgCl2. Cyclic AMP had relatively little effect on the hydrolysis of cGMP in CSF and the cortex, while cGMP inhibited hydrolysis of cAMP in both tissues. Snake venom was found to stimulate cAMP and cGMP phosphodiesterase activity of CSF, by 60% and 110% respectively. This stimulation by snake venom was also observed in the cortex phosphodiesterase, but was not observed in human plasma or thyroid phosphodiesterase. When CSF was applied to Sepharose 6B column, cGMP phosphodiesterase was separated into three different molecular forms. A plot of activity against substrate concentration using peak I (largest molecular size) revealed a high affinity (Km= 2.6μM) and a low affinity (Km= 100μM) for cAMP suggesting the existence of at least two molecular forms of the enzyme. On the other hand, using a cGMP as substrate the only one Km value (1.90 μm) was obtained. These Km values of CSF enzymes described above were close to those obtained from human cerebral cortex preparations. The enzyme under peak I corresponded to the cortex enzyme when judged from its molecular size and stimulation by snake venom. It seems likely from our results that at least a part of CSF phosphodiesterase originates from the central nervous system.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1975.tb07692.x
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