The effect of citrate and dihydroxyacetone on methanol oxidation in Hansenula polymorpha

Citrate and dihydroxyacetone inhibited [14C] incorporation from radioactive methanol to CO2 by washed cells of methylotrophic yeast Hansenula polymorpha grown in the media containing mixture of methanol with citrate or dihydroxyacetone, respectively. These results are discussed in connection with the earlier hypothesis on participation of the tricarboxylic acid cycle in the energy supply of the methylotrophic growth.     

A proposed mechanism for the stimulatory effect of bicarbonate ions on ATP synthesis in isolated chloroplasts

The effect of bicarbonate ions on induction of Mg²⁺-ATPase activity, on the N-ethylmaleimide inhibition of phosphorylation and on energy-dependent adenine nucleotide exchange has been examined with pea seedling chloroplasts. Incubation of chloroplasts with N-ethylmaleimide in the presence of 15 millimolar bicarbonate in the light results in enhanced inhibition of ATP synthesis when the preillumination pH is maintained between 7.0 and 7.5. Bicarbonate also enhances Mg²⁺-ATPase activity when it is included in the light-triggering stage at pH 7.0. The conditions (medium pH, bicarbonate concentration, etc.) for demonstrating the bicarbonate-induced enhancement of the N-ethylmaleimide inhibition and ATPase activity are similar to those required for the direct effect of bicarbonate on phosphorylation. Bicarbonate, under the same conditions, does not affect adenine nucleotide exchange (binding or release). It is concluded that the stimulatory effect of bicarbonate on ATP synthesis may be related to its ability to alter directly the conformation of the chloroplast coupling factor under conditions (suboptimal pH) where the enzyme shows minimal activity.     

The effect of testosterone on ascorbic acid synthesis in rooster comb

The level of “total” ascorbic acid (ascorbate+dehydroascorbate) has been measured in the mucoid layer of combs from normal roosters, capons and capons treated with testosterone. The “total” ascorbate level in capon comb was lower than the value obtained from combs from normal roosters. This value returned towards normal in combs from capons treated with testosterone. The specific activity of L-gulonate-NADP⁺ oxidoreductase, an enzyme in the pathway of ascorbate biosynthesis, also was measured. The specific activity levels followed a pattern similar to the ascorbate levels in the three types of combs utilized. The results are consistent with the possible role of L-ascorbic acid as a cofactor in the synthesis of collagen, a process which also appears to be dependent on the level of testosterone in the comb mucoid layer.     

The effect of testosterone and cadmium on the rat lateral prostate in organ culture

Organ culture of rat lateral prostate was performed in the presence of testosterone and cadmium. Maintenance of epithelial cells did not occur even in the presence of the androgen, but basal cells were stimulated and replaced original epithelium. Testosterone alone caused a partial differentiation of these basal cells. Cadmium alone was found to enter the epithelial and basal cells and subsequently cause necrosis. The metal was subcellularly located in the nucleus and within cytoplasmic organelles. Cadmium appears to compete with zinc in cultured lateral prostate and affects the differentiation and maintenance of the epithelial growth.     

ROS production and protein oxidation as a novel mechanism for seed dormancy alleviation

At harvest, sunflower (Helianthus annuus L.) seeds are dormant and unable to germinate at temperatures below 15 degrees C. Seed storage in the dry state, known as after-ripening, is associated with an alleviation of embryonic dormancy allowing subsequent germination at suboptimal temperatures. To identify the process by which dormancy is broken during after-ripening, we focused on the role of reactive oxygen species (ROS) in this phenomenon. After-ripening entailed a progressive accumulation of ROS, namely superoxide anions and hydrogen peroxide, in cells of embryonic axes. This accumulation, which was investigated at the cellular level by electron microscopy, occurred concomitantly with lipid peroxidation and oxidation (carbonylation) of specific embryo proteins. Incubation of dormant seeds for 3 h in the presence of hydrogen cyanide (a compound that breaks dormancy) or methylviologen (a ROS-generating compound) also released dormancy and caused the oxidation of a specific set of embryo proteins. From these observations, we propose a novel mechanism for seed dormancy alleviation. This mechanism involves ROS production and targeted changes in protein carbonylation patterns.     

Hormonal regulation of testicular prolactin receptors and testosterone synthesis in golden hamsters

A study was conducted with hypophysectomized hamsters to determine effects of administration of prolactin (PRL), luteinizing hormone (LH), and follicle-stimulating hormone (FSH)-alone or in combination-on testicular PRL receptors and in vitro testosterone production. Hormonal injections commenced the second day after hypophysectomy, and hamsters were killed on Day 5, approximately 13 h after the last hormonal injection. PRL receptor numbers were reduced by hypophysectomy, and PRL administration alone lessened the extent of this decrease. By themselves, neither LH nor FSH affected PRL receptors, but a combination of PRL + FSH + LH produced the greatest effect on these receptors. Receptor affinity was only modestly affected by any treatments. In vitro testosterone synthesis was measured after addition of 0, 2, 10, and 50 mIU of human chorionic gonadotropin (hCG) to incubations of testicular tissue. Neither PRL nor FSH by themselves in vivo affected basal or hCG-stimulated testosterone production. However, PRL + FSH increased (p less than 0.05) the magnitude of the in vitro testosterone response to hCG, as well as the sensitivity of that response (slope of the dose-response curve). LH alone increased both basal and hCG-stimulated testosterone production. PRL + LH provided no additional increase in the magnitude of the testosterone response, but increased (p less than 0.05) the sensitivity. PRL + FSH + LH in vivo provided for the greatest sensitivity of the testosterone response to hCG.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of cadmium administration in vivo on plasma testosterone and the ultrastructure of rat lateral prostate

Electron microscope microanalysis, atomic absorption analysis and ultrastructural survey were used to investigate the effects of parenteral cadmium administration on the lateral prostate of rats. Early fine structural changes in the epithelial cells of the prostatic tissue were associated with the detection of cadmium in the cellular organelles and alteration of the subcellular distribution of zinc. Involutionary changes appeared at later stages and differed from the usual castration effects. Basal cells did not regress with the altered physiological conditions but appeared to proliferate in the presence of cadmium. The observations are discussed in relation to the normal mechanisms which control the maintenance of the prostate gland.     

A proposed mechanism for nitrogen acquisition by grass seedlings through oxidation of symbiotic bacteria

In this paper we propose and provide evidence for a mechanism, oxidative nitrogen scavenging (ONS), whereby seedlings of some grass species may extract nitrogen from symbiotic diazotrophic bacteria through oxidation by plant-secreted reactive oxygen species (ROS). Experiments on this proposed mechanism employ tall fescue (Festuca arundinaceae) seedlings to elucidate features of the oxidative mechanism. We employed 15N₂ gas assimilation experiments to demonstrate nitrogen fixation, direct microscopic visualization of bacteria on seedling surfaces to visualize the bacterial oxidation process, reactive oxygen probes to test for the presence of H₂O₂ and cultural experiments to assess conditions under which H₂O₂ is secreted by seedlings. We also made surveys of the seedlings of several grass species to assess the distribution of the phenomenon of microbial oxidation in the Poaceae. Key elements of the proposed mechanism for nitrogen acquisition in seedlings include: 1) diazotrophic bacteria are vectored on or within seeds; 2) at seed germination bacteria colonize seedling roots and shoots; 3) seedling tissues secrete ROS onto bacteria; 4) bacterial cell walls, membranes, nucleic acids, proteins and other biological molecules are oxidized; 5) nitrates and/or smaller fragments of organic nitrogen-containing molecules resulting from oxidation may be absorbed by seedling tissues and larger peptide fragments may be further processed by secreted or cell wall plant proteases until they are small enough for transport into cells. Hydrogen peroxide secretion from seedling roots and bacterial oxidation was observed in several species in subfamily Pooideae where seeds possessed adherent paleas and lemmas, but was not seen in grasses that lacked this feature or long-cultivated crop species.     

The effect of exercise on the production and clearance of testosterone in well trained young men

Tritium-labelled testosterone was infused into four well-trained subjects at rest and during one hour of exercise at about 60% of their maximum aerobic power. This exercise regime led to a mean increase of 27% (range 10-51%) in plasma testosterone concentration. At the same time there were significant decreases in the estimated hepatic plasma flow (EHPF) (45%; range 28-67%), metabolic clearance rate of testosterone (MCRT) (29%; range 18-37%) and plasma volume (8.2%; range 3-10%). The production rate of testosterone decreased by 10% (range 9-22%) but this was not statistically significant. The ratio MCRT:EHPF increased in 3 out of 4 subjects in response to exercise but there was considerable inter-subject variation both at rest and during exercise. These findings suggest that the exercise-induced elevation of testosterone level is due solely to the reduction in the rate at which testosterone is cleared from the plasma. The principal cause of the reduction in MCRT is probably the reduction in EHPF but the variation in the ratio MCRT:EHPF suggests that changes in the extrahepatic clearance of testosterone may also be involved.     

Inhibitory effect of glycyrrhetinic acid on testosterone production in rat gonads

We studied the effects of shakuyaku-kanzo-toh (a Chinese herbal medicine) and its components on testosterone production by rat gonads. We used paeoniflorin as a main component of shakuyaku (paeoniae radix), glycyrrhizin as a main component of kanzo (glycyrrhizae radix) and glycyrrhetinic acid as a main metabolite of glycyrrhizin. Oral administration of shakuyaku-kanzo-toh, glycyrrhizin, and glycyrrhetinic acid decreased in vitro basal testosterone production in Leydig cells by LH stimulation. Glycyrrhizin and glycyrrhetinic acid caused a significant decrease in testosterone production with an accumulation of 17 alpha-hydroxyprogesterone when incubated with isolated Leydig cells, while paeoniflorin showed no such effect. The inhibitory effect of glycyrrhetinic acid was far more potent than that of glycyrrhizin, causing about 90% inhibition at 10 micrograms/ml. Glycyrrhizin and glycyrrhetinic acid did not change the cyclic AMP or progesterone level in the Leydig cells. When 14C-labeled androstenedione was incubated with microsomal fraction of testicular or ovarian tissue, glycyrrhizin and glycyrrhetinic acid inhibited the conversion of androstenedione to testosterone, indicating that these compounds inhibit the activity of 17 beta-hydroxysteroid dehydrogenase (EC. 1.1.1.64). The ED50 of glycyrrhetinic acid was about 4 microM.     

The regulation of fatty acid and branched-chain amino acid oxidation in cancer cachectic rats: a proposed role for a cytokine, eicosanoid, and hormone trilogy

Some postulates of a hypothesis concerned with the deregulation of muscle turnover by the hypoketonemia of cachectic tumor-bearing rats were examined. Plasma concentrations of ketone bodies (D-(3)-hydroxybutyrate + acetoacetate) in rats bearing the Walker 256 carcinosarcoma were reduced by 45% (P less than 0.001) whereas the concentrations of triglyceride and free fatty acids were elevated by 223% (P less than 0.001) and 335% (P less than 0.001), respectively. Parallel with the changes in plasma, the livers of tumor-bearing animals showed decreased concentrations of KB by 35% (P less than 0.05) and increased concentrations of TG and FFA by 49% (NS) and 15% (NS), respectively. In comparison with values for the control liver (fed ad libitum), the perfused liver of animals bearing the Walker 256 tumor formed 42% (P less than 0.05) and 75% (P less than 0.05) less ketone bodies and CO2, respectively, from oleate, while TG formation was enhanced by 33% (P less than 0.001). There was two- to threefold (P less than 0.001) enhancement of [1-14C]leucine oxidation in vivo by the tumor-bearing animals. The activities of branched-chain amino acid aminotransferase and branched-chain keto acid dehydrogenase were elevated by 70% (P less than 0.001) and 560% (P less than 0.001) respectively in the gastrocnemius muscle of the tumor-bearing animals. The results of the investigation supported a second proposal of the hypothesis, namely, that cancer-induced cachexia resulted in the notable elevation in the concentration of arginine vasopressin that was accompanied by parallel increases in the plasma, urine, and muscle concentrations of prostaglandin E2. The proposals of the original hypothesis have been augmented to include roles for PGE2 and the cytokine cachectin/tumor necrosis factor which may engineer all of the events depicted in the original hypothesis.