The relationship between the activity of chloroplast Photosystem II and the midpoint oxidation-reduction potential of cytochrome b-559

The role of cytochrome b-559 in Photosystem II reactions has been investigated using hydroxylamine treatment of chloroplast membranes. Incubation of chloroplasts with hydroxylamine in darkness resulted in inhibition of water oxidation and a decrease in the amplitude of cytochrome b-559 reducible by hydroquinone. The loss of water oxidizing activity perfectly correlated with the decrease in amplitude of cytochrome b-559 reduction. Potentiometric titration of cytochrome b-559 after hydroxylamine treatment revealed a component with E_m7.8 at +240 mV in addition to a lower potential species at +90 mV. This compared to control chloroplasts in which cytochrome b-559 exists in the typical high potential state, E_m7.8 = +383 mV, in addition to some of the low potential (E_m7.8 = +77 mV) form. Photosystem II activity could be further inhibited by incubation with hydroxylamine in the light. In these chloroplasts only low rates of photooxidation of artificial electron donors were observed compared to ‘dark’ chloroplasts. In addition, the hydroxylamine light treatment caused a further change in cytochrome b-559 redox properties; a single component, E_m7.8 = 90 mV is seen in titration curves. The role of cytochrome b-559 in Photosystem II functioning is discussed on the basis of these observations which suggest a dependence of photooxidizing ability of Photosystem II on the redox properties of this cytochrome.     

Maternal transfer of photoperiodic information in Siberian hamsters. V. Effects of melatonin implants are dependent on photoperiod.

Photoperiodic information is transferred from female Siberian hamsters to their fetuses during gestation. Although maternal melatonin is known to be essential for the transfer of prenatal photoperiodic information, its specific role is not well defined. The duration of the daily melatonin signal, expressed as an elevation of serum melatonin levels in the maternal circulation, has been hypothesized to convey day length information to the fetus. If this hypothesis is valid, it predicts that identical maternal melatonin signals should affect the fetuses identically, regardless of the prenatal photoperiod. To test this hypothesis, adult females received melatonin in beeswax or beeswax alone. They were paired with males and housed in photoperiods of 12L:12D or 16L:8D. On the day of parturition, mother and young were transferred to constant light (LL). Young males were killed on Day 28 of life, and weights of testes were determined. Prenatal treatment with beeswax alone did not affect the nature of the signal transferred from mother to fetus; young gestated in 12L:12D and reared in LL developed small testes, while those gestated in 16L:8D had large testes. On the other hand, the effect of the prenatal melatonin treatment on postnatal testicular development in LL was inversely dependent on the prenatal photoperiod: testicular growth was stimulated in young gestated in 12L:12D, but inhibited in young gestated in 16L:8D. To verify that the melatonin pellets produced equivalent serum melatonin levels in adult females in 12L:12D and 16L:8D, unmated adult females were killed 6-10 wk after receiving melatonin pellets. Serum levels were elevated in both groups throughout the day and night.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of exercise training and chronic glyburide treatment on glucose homeostasis in diabetic rats.

Exercise training and sulfonylurea treatment, either individually or in combination, were evaluated for their effects on plasma glucose concentrations, oral glucose tolerance, and glucose clearance in the perfused hindquarter of diabetic rats. Female rats that were injected with streptozocin (45 mg/kg iv) and had plasma glucose concentrations between 11 and 25 mM were considered diabetic and divided into sedentary, glyburide-treated, exercise-trained, and glyburide-treated plus exercise-trained groups. The sedentary streptozocin-treated rats were severely diabetic, as indicated by elevated glucose concentrations, impaired insulin response during oral glucose tolerance tests, and lower rates of glucose clearance in hindlimb skeletal muscle. Neither 8 wk of exercise training nor 4 wk of glyburide treatment alone improved these parameters. In contrast, the diabetic rats that were both trained and treated with glyburide showed some improvement in glucose homeostasis, as evidenced by lower plasma glucose concentrations, an enhanced insulin response to an oral glucose load, and a decrease in the severity of skeletal muscle insulin resistance compared with the diabetic controls. These data suggest that glyburide treatment or exercise training alone does not alter glucose homeostasis in severely insulin-deficient diabetic rats; however, the combination of exercise training and glyburide treatment may interact to improve glucose homeostasis in these animals.     

Prevention of thromboxane B2-induced hepatocyte plasma membrane bleb formation by certain prostaglandins and a proteinase inhibitor

Isolated hepatocytes incubated in the presence of thromboxane B2 developed many plasma membrane blebs which are a characteristic feature of toxic or ischaemic cell injury. When hepatocytes were incubated in the presence of both thromboxane B2 and the non-lysosomal proteinase inhibitor, leupeptin, were also well protected from the formation of blebs. This implies that thromboxane B2 is able to activate non-lysosomal proteinases which appear to attack certain cytoskeletal proteins. The data presented are consistent with thromboxane B2 acting as an intermediary in a proposed mechanism of cell injury and death in which elevated cytosolic free Ca2+ levels activate phospholipase A2 and the arachidonic acid cascade.     

Carbon-13 NMR relaxation studies of pre-melt structural dynamics in [4-13C-uracil] labeled E. coli transfer RNAIVal.

We report 67.8 MHz carbon-13 spin-lattice relaxation studies on [4-13C-uracil] labeled tRNAIVal purified from E. coli SO-187. Following 13C-enriched C4 carbonyl resonances from modified and unsubstituted uridines scattered throughout the polymer backbone enables us to determine dynamical features in both loop and helical stem regions. The experimental results have been analyzed in terms of a model of isotropic overall molecular reorientation. "Anomalous" residues for which the experimental data cannot be accounted for in terms of the model provide an assessment of local and regional properties. Thus, "native" tRNAIVal under physiological conditions of magnesium (10 mM) and temperature (20 degrees - 40 degrees C), exhibits the following characteristics: 1) uridines held rigidly in helical stems and tertiary interactions display correlation times for rotational reorientation of 15-20 nsecs, typical for overall tRNA motion; 2) uridines in loops such as the wobble residue uridine-5-oxyacetic acid (V34) are quite accessible to solvent; moreover V34 and another loop residue, D17, exhibit local mobility; 3) the tertiary interactions involving 4-thio uridine (s4U8) and A14 and ribothymidine (rT54) and A58 are weakened as temperature increases.     

Light-dependent quenching of chlorophyll fluorescence in pea chloroplasts induced by adenosine 5′-triphosphate

Addition of ATP to chloroplasts causes a reversible 25–30% decrease in chlorophyll fluorescence. This quenching is light-dependent, uncoupler insensitive but inhibited by DCMU and electron acceptors and has a half-time of 3 minutes. Electron donors to Photosystem I can not overcome the inhibitory effect of DCMU, suggesting that light activation depends on the reduced state of plastoquinone. Fluorescence emission spectra recorded at ?196°C indicate that ATP treatment increases the amount of excitation energy transferred to Photosystem I. Examination of fluorescence induction curves indicate that ATP treatment decreases both the initial (F_o) and variable (F_v) fluorescence such that the ratio of F_v to the maximum (F_m) yield is unchanged. The initial sigmoidal phase of induction is slowed down by ATP treatment and is quenched 3-fold more than the exponential slow phase, the rate of which is unchanged. A plot of F_v against area above the induction curve was identical plus or minus ATP. Thus ATP treatment can alter quantal distribution between Photosystems II and I without altering Photosystem II-Photosystem II interaction. The effect of ATP strongly resembles in its properties the phosphorylation of the light-harvesting complex by a light activated, ATP-dependent protein kinase found in chloroplast membranes and could be the basis of physiological mechanisms which contribute to slow fluorescence quenching in vivo and regulate excitation energy distribution between Photosystem I and II. It is suggested that the sensor for this regulation is the redox state of plastoquinone.     

Cerebral Glutamic Acid Decarboxylase Activity and γ-Aminobutyric Acid Concentrations in Mice Susceptible or Resistant to Audiogenic Seizures

Abstract: DBA/2 mice between 21 and 28 days of age are highly susceptible to sound-induced seizures. Drug studies suggest a possible deficit of γ-Aminobutyric acid (GABA)-mediated neurotransmission may be involved. We have measured the whole brain GABA concentration and glutamic acid decar-boxylase activity in DBA/2 mice at various ages before, during, and after the period of maximal susceptibility to audiogenic seizures. Corresponding determinations were carried out on age-matched TO mice, a strain much less susceptible to audiogenic seizures than DBA/2 mice at all ages. No significant differences in GABA concentration or glutamic acid decarboxylase activity were found between strains at any age. The susceptibility of DBA/2 mice to audiogenic seizures does not result from a gross inability to synthesise or store GABA.     

Enzymic lipid peroxidation in the microsomal fraction of rat brain

Abstract: An enzymic lipid peroxidation system has been demonstrated in the microsomal fraction of rat brain and the requirements and optimal conditions for assay determined. The involvement of NADPH-cytochrome c reductase was demonstrated in vesicles reconstituted with lipids extracted from the brain microsomal fraction. Further characterization of the system made use of substances shown to inhibit the liver microsomal system. α-Tocopherol was shown to be an effective inhibitor of lipid peroxidation in the brain microsomal system, whereas Na₂SO₃ had no effect, which is indicative that free radical transfer occurs only in the hydrophobic regions. Neither superoxide dismutase nor catalase inhibited lipid peroxidation. The implications of an NADPH-cytochrome c reductase-dependent lipid peroxidation system that is not linked to a drug hydroxylation system and appears to differ from the liver microsomal system in a number of other ways are discussed.     

Evidence for a dual action of converting enzyme inhibitor on blood pressure in normal man

We studied the effect of a converting enzyme inhibitor (CEI), Captopril SQ 14,225 50 mg p.o. in eight supine normal subjects under a high sodium (150 mEq/d) and low sodium (25 mEq/d) diet. On high sodium, plasma renin (PRA) and aldosterone were basal and Saralasin did not lower mean blood pressure. However, CEI induced an 11.4 +/- 3.2 mm fall in blood pressure (p less than 0.02) and either indomethacin 50 mg or ibuprofen 800 mg (PI), when given simultaneously on another day abolished the blood pressure response (2.5 +/- 0.9 mm Hg, p greater than 0.5). In contrast, on a low salt diet where renin was increased, CEI induced a drop in blood pressure which was not significantly altered by PI (12.8 +/- 1.1 vs. 10.0 +/- 3.1 mm Hg, p greater than 0.5). CEI increased plasma renin on both diets (1.7 +/- 0.5 to 3.5 +/- 0.8 and 2.8 +/- 0.6 to 12.5 +/- 3.1 ng/ml/hr respectively both p less than 0.05). Aldosterone did not change (high Na+) or fell (low Na+). Inhibition of Prostaglandin synthesis did not significantly block the renin rise from CEI suggesting that the direct angiotensin II negative feedback is relatively independent of acute prostaglandin release. Our studies suggest that CEI has a dual hypotensive action. In a low renin state, the hypotensive action appears to be mediated through vascular prostaglandins.     

Carbon-13 NMR studies on [4-13C] uracil labelled E. coli transfer RNA1(Val1).

In this paper we describe carbon-13 nuclear magnetic resonance results on 13C-enriched purified transfer RNAI(VAL) from from E. coli SO-187, a uracil requiring auxotroph. The organism was grown on uracil 90% 13C-enriched at the carbonyl C4 position. Transfer RNAI(Val) was purified from bulk tRNA by sequential chromatography on columns of BD cellulose, DEAE-Sephadex A-50 and reverse gradient sepharose 4B. Dihydrouridine, 4-thiouridine, and uridine 5-oxyacetic acid located at discrete positions in the polymer backbone were tentatively assigned in the highly resolved 25 MHz 13C-spectra. Chemical shift versus temperature plots reveal differential thermal perturbation of the ordered solution structure, evident in the large dispersion (ca 3-4 ppm) of the uridine C4 resonances. Over the range 26-68 degrees C, V in the anticodon displays the largest downfield shift. Whereas several uridine residues rapidly shift downfield between 50-68 degrees, one moves upfield beginning at 37 degrees. The results are qualitatively compared with proton NMR analysis of the three dimensional structure.