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The possible regulatory role of tetrahydrobiopterin (BH 4 ) in Type III nitric oxide synthase (NOS III) activity of human placentae from first trimester, term and pre-eclamptic pregnancies was investigated. In homogenates of first-trimester or term placentae, BH 4 stimulated NOS III activity up to 2.5-fold in a concentration dependent manner from 20n m to 1μm BH 4 , and half-maximal...
We have found in a previous study that 5-50 μm tetrahydrobiopterin (BH 4 ) stimulated 1.2-2.5-fold Ca 2+ -dependent nitric-oxide synthase (NOS) activity in homogenates prepared from primordial human placentae. Now we report on the dramatic, about sixfold, activating effect of BH 4 on this activity measured in microsomal preparations. Firstly, both in the absence and presence...
Homogenized first trimester human placenta exhibits both Ca 2+ -dependent (90–95 per cent) and Ca 2+ -independent (5–10 per cent) nitric oxide (NO)-synthesizing activities. Addition of tetrahydrobiopterin (BH 4 ) to homogenates containing Ca 2+ in maximally activating concentrations (>0.5 μm) results in a further 2–2.5-fold activation of NO synthesis, with half-maximal...