Mechanism of iodide-dependent catalatic activity of thyroid peroxidase and lactoperoxidase.

Mechanisms that have been proposed for peroxidase-catalyzed iodination require the utilization of 1 mol of H2O2 for organic binding of 1 mol of iodide. When we measured the stoichiometry of this reaction using thyroid peroxidase or lactoperoxidase at pH 7.0, we consistently obtained a ratio less than 1.

Iodide-dependent catalatic activity of thyroid peroxidase and lactoperoxidase.

Thyroid peroxidase (TPO) and lactoperoxidase (LPO) display significant catalatic activity at pH 7.0 in the presence of low concentrations of iodide, based both on measurements of H2O2 disappearance and O2 evolution. In the absence of iodide only minor catalatic activity was detected.

Automated scanning of 14C on polyacrylamide gel.

Cylindrical polyacrylamide gels were automatically analyzed for radioactive 14C using a commercially available radiochromatogram scanner. This method was capable of detecting peaks of [14C]protein containing 50 000--1 000 000 cpm. Under optimal conditions, gels could be scanned at a rate of 1 cm per min, allowing for analysis of 20--30 gels per day.

Light-induced exchange of nucleotides into coupling factor 1 in spinach chloroplast thylakoids.

The method of centrifugation of chloroplast thylakoids through silicone fluid, previously used to estimate the uptake of solutes by thylakoids, is shown to be an excellent method for measuring binding of nucleotides to thylakoids. This binding, which is probably an exchange (Harris, D. A.

Dynamically produced refractive-index variations with thickness of volume holograms in electrooptic crystals.

Dynamic theory of volume holography is used to calculate the variations in the thickness direction of the hologram-constituting refractive-index modulation and the externally observable effects of these variations in electrooptic materials. It is shown that thick holographic gratings may exhibit significant amplitude and grating phase variations with thickness including amplitude sign reversal. These nonuniformities strongly affect holographic grating recording and readout characteristics such as maximum possible diffraction efficiency and angular selectivity.

Acid-induced phosphorylation of adenosine 5'-diphosphate bound to coupling factor 1 in spinach chloroplast thylakoids.

Adenosine 5'-diphosphate, bound to coupling factor 1 (CF1) in spinach chloroplast thylakoids, is in part converted to adenosine 5'-triphosphate, upon injection of the thylakoids into strong acids in the dark. Bound phosphate serves as the phosphoryl donor for this uncoupler-insensitive conversion. Exposure of the thylakoids to heat or to urea prior to their injection into acid caused dissociation of ADP and prevents the apparent acid-induced synthesis of ATP.

Influence of adenine nucleotides on the inhibition of photophosphorylation in spinach chloroplasts by N-ethylmaleimide.

The incubation of spinach chloroplasts with 1 mM N-ethylmaleimide in light for 60 to 90 s results in a partial, irreversible inhibition of photophosphorylation. The inhibition was not overcome at infinite light intensity or at infinite concentrations of the phosphorylation substrates. Although the inhibition diminished with decreasing concentrations of adenosine diphosphate in the assay of phosphorylation, the inhibition of guanosine diphosphate phosphorylation was independent of the concentration of this nucleotide.