A BSTR ACTThe nitric-oxide synthase (NOS; EC 1.14.13.39) reaction is formulated as a partially tetrahydrobiopterin (H 4 Bip)-dependent 5-electron oxidation of a terminal guanidino nitrogen of L-arginine (Arg) associated with stoichiometric consumption of dioxygen (O 2 ) and 1.5 mol of NADPH to form L-citrulline (Cit) and nitric oxide (⅐NO). Analysis of NOS activity has relied largely on indirect methods such as quantification of nitrite͞nitrate or the coproduct Cit; we therefore sought to directly quantify ⅐NO formation from purified NOS. However, by two independent methods, NOS did not yield detectable ⅐NO unless superoxide dismutase (SOD; EC 1.15.

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Attempts by previous investigators to measure the dielectric constant and electrical conductivity of moist rock and soil samples in the laboratory have produced unexpectedly high values of dielectric constant at low frequencies. These high values have been attributed to measurement error by some critics, making their validity subject to doubt. The present investigation was made to trace the source of the suspected errors and eliminate them if possible. The study resulted in the development of electrochemically reversible electrodes that appear to minimize measurement errors of previous investigators. Measurements were made with the new electrodes over the frequency range 10² to 106 cps using a group of rock and soil samples containing various amounts of moisture. Values of dielectric constant were quite high at low frequencies but were lower than the values obtained by previous methods by as much as an order of magnitude. Statistical correlations were made and empirical equations were derived by computer that gave the following relationships: σ = ƒ(ƒ,w), ϵ/ϵ0 = ƒ(ƒ,w), and ϵ/ϵ0 = ƒ(ƒ, σ100), where σ is conductivity, ϵ/ϵ0 is dielectric constant, ƒ is frequency, w is water content, and σ100 is conductivity measured at 100 cps.

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