???EFFECTS OF SODIUM NITROPRUSSIDE AND NITRITE ON OUABAINE-SENSITIVE Na+, K+-АТРase
ACTIVITY OF MYOMETRIUM SMOOTH MUSCLE
Palladin Institute of Biochemistry, National Academy of Science of Ukraine, Kyiv;
Effective inhibiting effect of sodium nitroprusside and nitrite on Na+, K+-ATPase enzymatic activity of miometrium sarcolemma fraction was shown. Seeming Ki was of micromolar and submicromolar magnitudes. Investigations with sodium nitroprusside demonstrated an uncompetitive inhibition for ATP (growth of affinity for ATP and decrease of maximal velocity) and mixed inhibition for cations (decrease of maximal velocity and activation of constant for K+). Inhibitory effect of ouabain was reduced in the presence of sodium nitroprusside; ditiothreitol prevented enzyme inactivation by sodium nitroprusside. Kinetic analysis of experimental results using ouabain and ditiothreitol suggests chemical modification of enzyme sulfhydryl groups. Resistant component of Na+, K+-ATPase activity, which is sensitive to the action of detergent digitonine, was observed.
In comparative investigations with postnucleus fraction stimulating actions of sodium nitroprusside, sodium nitrite, cGMP (more enhance) were shown. Methylene blue (soluble guanilatecyclase inhibitor) prevented the activation of Na+, K+-ATPase activity by sodium nitrite. We suppose that the way of enzyme activation is prevalent in the condition of the moderate formation of nitric oxide and in the absence of hyper(over)production of reactive oxygen species.
Key words: nitric oxide, smooth muscle, Na+, K+-АТРase, cGMP.
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