Role of lipoxygenase in the O2-dependent activation of soluble guanylate cyclase from rat lung

Abstract

Guanylate cyclase activity in rat lung supernatant fractions is stimulated 3-4 fold by aerobic incubation at 30 degrees C for approx. 30 min ('O2-dependent activation'). This stimulation was blocked by 20 microM-eicosa-5,8,11,14-tetraynoic acid (ETYA), an inhibitor of lipoxygenase and cyclo-oxygenase, but not by aspirin or indomethacin, which are cyclo-oxygenase inhibitors. The enzyme activator(s) is presumed to be the fatty acid hydroperoxide(s) formed by lipoxygenase. Removal of lipoxygenase from the supernatant fraction by chromatography on Amberlite XAD-4 also prevented activation, which was restored by the addition of soya-bean lipoxygenase. Bovine serum albumin prevented O2-dependent activation or activation by soya-bean lipoxygenase, through its ability to bind the unsaturated fatty acid substrate of lipoxygenase. The lipoxygenase in the supernatant fraction is inhibited by endogenous glutathione peroxidase plus reduced glutathione (GSH); removal of GSH de-inhibits lipoxygenase and activates guanylate cyclase. This was effected by autoxidation, by cumene hydroperoxide (with GSH peroxidase) and by titration with N-ethylmaleimide (NEM). Activation by NEM was inhibited by serum albumin or ETYA, as was activation by low concentrations (less than 50 microM) of cumene hydroperoxide. Activation by higher concentrations was not so inhibited; therefore, cumene hydroperoxide can also activate by a direct effect on guanylate cyclase. A hypothesis for physiological activation is proposed.

Mediators produced by the endothelial cell.

“…255 In contrast, hemoglobin 206 -207 inhibits the vasorelaxant action of NO, SIN-1, GTN, and sodium nitroprusside. Hemoglobin is a direct inhibitor of the active ferroheme center of guanylate cyclase 256 and also effectively removes NO from solution. 257 The vasorelaxant actions of EDRF are antagonized by both methylene blue and hemoglobin.…”

Neurochemical Approaches to the Pathogenesis of Down's Syndrome

“…Apart from the likelihood of alterations in membrane fluidity due to LPX underlying disorders of cellular function in DS, there is now also the interesting possibility that abnormal activation of guanylate cyclase may occur in trisomy 21 as a result of the uncompensated SOD activity and associated LPX. Guanylate cyclase is activated by SOD (Mittal & Murad,1977;Yoshikawa & Kuriyama, 1980), and it is now believed that products of the peroxidation of PUFA are physiological regulators of guanylate cyclase in many tissues (Murad et al, 1979;Craven & De Rubertis, 1982;Leiber & Harbon, 1982;White, Karr & Patt, 1982;Bromberg & Pick, 1983;Sobolev, Tertov & Rybalkin, 1983). Such effects may explain why T-lymphocytes of younger DS patients resemble those of elderly normal subjects in exhibiting markedly elevated levels of cGMP, a finding that has been related to the signs of immunodeficiency that occur alike in normal aging and in DS (Tam & Walford, 1980;.…”

Pharmacological studies on STb heat-stable enterotoxin in pig and rat jejunum

“…Thus arachidonic acid is released from phospholipids or diacylglycerol is converted to endoperoxides or hydroperoxides all known to be activators of guanylate cyclase (Spies et al, 1980White et al, 1982.…”