ISSN:
1573-4919
Keywords:
ions
;
nitric oxide
;
retina
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Abstract The divalent cation requirements of NOS activity in bovine retina homogenate supernatant were investigated. Supernatants were assayed under standard conditions (in mM: EDTA 0.45, Ca2+ 0.25, Mg2+ 4.0). In order to investigate the enzyme's dependence on divalent cations, the tissue homogenate was depleted of di- and trivalent cations by passing it over a cation-exchange column (Chelex 100). Surprisingly, NOS activity was 50-100% higher in this preparation. However, addition of either EDTA (33 μM) or EGTA (1 mM) almost fully inhibited NOS activity, suggesting a requirement for residual divalent metal cation(s). Phenanthroline or iminodiacetic acid at low concentrations had little effect on activity, suggesting no requirement for Fe2+, Zn2+ or Cu2+. Ca2+ had a moderate stimulatory effect, with an optimum activity around 0.01 mM. Mg2+ or Mn2+ had little effect at concentrations 〈 0.25 mM. However, in the presence of EDTA, Mn2+ or Ca2+ markedly stimulated NOS activity with the optimum at 0.1 mM. At high concentrations (〉 0.1-0.2 mM), all divalent cations tested (Ba2+, Zn2+, Co2+, Mn2+, Mg2+, Ca2+), as well as La3+, dose-dependently inhibited NOS activity. We propose that retinal NOS requires low concentrations of naturally occurring divalent metal ions, most probably Ca2+, for optimal activity and is inhibited by high di- and trivalent metal concentrations, probably by competition with Ca2+.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1007037307370
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