Peptide-receptor protein relationships: importance in estradiol feedback

Aspartate, glutamate, serine and glycine all permeate the inner membrane of mitochondria isolated from both etiolated and green plant tissues. No significant difference was found in the transport characteristics shown by mitochondria from either tissue. Influx of each amino acid appears diffusional because substrate saturation was not observed and there was no indication of specific inhibition or a requirement for a compensatory or counter ion for uptake. In contrast, uptake of the keto acid pyruvate did appear saturable. Inhibition by α-cyano-4-hydroxycinnamate, mersalyl and FCCP, but not valinomycin, suggests a carrier and a ΔpH mediate pyruvate transport into the matrix.     

Direct electrochemical oxidation of Clostridium pasteurianum ferredoxin: Identification of facile electron-transfer processes relevant to cluster degradation

Rapid oxidation processes relevant to the degradation of [4Fe4S] clusters in Clostridium pasteurianum ferredoxin were studied via direct (unmediated) heterogeneous electron transfer at a pyrolytic graphite electrode. Differential-pulse voltammograms of native [4Fe4S] ferredoxin showed two well-defined oxidation peaks corresponding to apparent E-values of +793 and +1120 mV at 5°C. Direct involvement of the cluster was established through parallel experiments with the 2[4Fe4Se] derivative for which peak positions were shifted. Square-wave voltammetry showed that the product of the first electron transfer, which may correspond to the ‘super-oxidised’ [4Fe4S]³⁺ oxidation level, undergoes rapid degradation (t_{$\text{1}\text{2}$} < 1.6 ms at 5°C). The second oxidation process, as characterised by a significant (?100 mV) negative shift upon selenium substitution, very likely represents oxidation of S(Se) still associated with the protein and possibly contained within the remaining FES(Se) substructure.     

Biosynthesis of Prostacyclin in Rat Cerebral Microvessels and the Choroid Plexus

Abstract: Microvessels, predominantly capillaries, were isolated from rat cerebrum by a modification of published procedures. The morphology and purity of the preparations were monitored by light and electron microscopy and by enrichment in alkaline phosphatase, γ-glutamyl transpeptidase, and prostacyclin synthetase. A reversed-phase high-pressure liquid chromatographic method was used in the purification of prostaglandins after extraction from aqueous incubation solutions. Prostacyclin synthesis in brain is localized in cerebral blood vessels and capillaries. The endogenous biosynthetic capacity of the isolated cerebral capillary fractions for prostacyclin, measured as its chemically stable breakdown product, 6-keto-prostaglandin F_1α, was 11 ng/mg protein/10 min. Choroid plexus and intact surface vessels synthesized 6-keto-prostaglandin F_1α at 37 and 35 ng/mg protein/10 min, respectively. The prostacyclin-synthesizing enzyme of the cerebral capillaries also converted the exogenously added prostaglandin endoperoxides to 6-keto-prostaglandin F_1α. Comparison of the synthesis of prostaglandins 6-keto-F_1α, E₂, and F_2α showed that 6-keto-prostaglandin F_1α was the major prostaglandin formed in the microvessels, in the larger surface vessels, and in the choroid plexus. Prostaglandin D₂ was not detected. Prostacyclin synthesis by the cerebral vasculature is similar to that in other blood vessels and cultured human endothelial cells. Possible physiological roles of prostacyclin in the cerebral microvasculature are discussed with special regard to the autoregulation of cerebral blood flow.