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PubMed2004

Autocrine regulation of insulin secretion in human ejaculated spermatozoa.

A striking feature of insulin expression is its almost complete restriction to beta-cells of the pancreatic islet in normal mammals. Here we show that insulin is expressed in and secreted from human ejaculated spermatozoa. Both insulin transcript and protein were detected. In addition, the large differences in insulin secretion, assessed by RIA, between noncapacitated and capacitated sperm suggest a role for insulin in capacitation. Insulin had an oscillatory secretory pattern involving glucose dose-dependent increases and significant decreases during the blockage of an insulin autocrine effect. It appears that the effect of glucose on the fertilizing ability of sperm is mediated by glucose metabolism through the pentose phosphate pathway. Then we evaluated the autocrine effect of sperm insulin on glucose metabolism by studying the activity of glucose-6-phosphate dehydrogenase, the key rate-limiting enzyme in the pentose phosphate pathway. The simultaneous decrease in both insulin release and glucose-6-phosphate dehydrogenase activity induced by blocking the autocrine insulin effect with three different procedures (blockage of insulin release by nifedipine, immune neutralization of the released insulin by antiinsulin serum, and blockage of an insulin intracellular effector such as phosphotidylinositol 3-kinase by wortmannin) strongly suggests a physiological role of sperm insulin on these two events. Insulin secretion by spermatozoa may provide an autocrine regulation of glucose metabolism based on their energetic needs independent of systemic insulin. In conclusion, these data open a new area of study in male reproduction.

Autocrine Communication↗
PubMed1992

Effects of luteinizing hormone on glucose metabolism in cumulus-enclosed bovine oocytes matured in vitro.

The effects of LH on glucose metabolism within cumulus cell-enclosed bovine oocytes were determined. Cumulus cell-enclosed bovine oocytes were matured in vitro (IVM) in control medium alone or supplemented with LH, FSH, or TSH, then individually assayed for the metabolism of D-[5-3H]glucose, D-[1-14C]glucose, D-[6-14C]glucose, and D-[U-14C]glucose. Glycolytic activity was unchanged after IVM in 1 microgram LH/ml, but was greater (P < 0.05) after culture in 10 and 50 micrograms LH/ml than the control value (1.34 +/- 0.13, 1.87 +/- 0.20, and 1.63 +/- 0.14 vs. 1.19 +/- 0.13 nmol 3H2O/micrograms protein.3 h, respectively). Increased glycolytic activity was observed within cumulus cell-enclosed oocytes, but not in cumulus cell complexes from which the oocyte was removed. Also, no glycolysis was detected when denuded oocytes from any IVM treatment were assayed. Glycolytic activity was greater (P < 0.01) after IVM in LH (10 micrograms/ml) vs. TSH (0.5 microgram/ml), FSH (1.0 micrograms/ml), and control treatments (3.04 +/- 0.10, 2.44 +/- 0.10, 2.33 +/- 0.10, and 2.13 +/- 0.10 nmol 3H2O/micrograms protein.3 h, respectively). Treatment with TSH also increased (P < 0.05) glycolytic activity compared to control values. Relative to control values after IVM, pentose cycle activity was 73.6% less, 2.9% higher, and 33.9% higher with LH, FSH, and TSH treatments, respectively. Total 14CO2 generated from D-[U-14C]glucose did not differ between treatments. Glucose oxidation by the pentose cycle accounted for 30.5%, 29.7%, 40.7%, and 11.1% of the total 14CO2 production after IVM in control medium, FSH, TSH, or LH, respectively. Data indicate that IVM with LH results in increased glycolytic activity and mitochondrial glucose oxidation within cumulus cell-enclosed bovine oocytes, and that this may represent a mechanism by which LH enhances oocyte maturation.

Animals↗
PubMed1984

Inhibitory effect of 6-aminonicotinamide on the renal transport of para-aminohippurate in the rat.

In this study, we investigated the effect of 6-aminonicotinamide (6-AN), a typical potent inhibitor of the pentose phosphate pathway, on the renal transport of para-aminohippurate (PAH) in the rat. The contents of adenosine-triphosphate (ATP) and 6-phosphogluconate (6-PG) in the kidney were measured at intervals of 2 hours after the administration of 6-AN (75 mg/kg body weight, i.p.). It was found that the 6-PG content in the kidney rapidly increased and reached a plateau at the fourth hour after the administration, with this level being maintained up to the eighth hour. In contrast, the ATP content was found to remain normal up to the sixth hour, after which it significantly decreased as time elapsed. Furthermore, additional experiments were carried out by loading the rat with a high concentration of PAH solution at 6 hours after the administration of 6-AN. The renal tubular secretion maximum for PAH was significantly depressed in the 6-AN group in comparison to the control. These results suggest that this depression in renal PAH secretion capacity was partially due to the inhibition of the pentose phosphate pathway in the kidney, but not due to the change of renal ATP level.

6-Aminonicotinamide↗
PubMed1995

Transgalactosylation catalyzed by alpha-galactosidase from Candida guilliermondii H-404.

The thermostable alpha-galactosidase from Candida guilliermondii H-404 synthesized self-transfer products in the absence of a suitable acceptor. The main self-transfer product, using melibiose as a donor substrate, was O-alpha-D-galactosyl-(1,6)-O-alpha-D-galactosyl-(1,6)-D-glucose. This enzyme had a wide acceptor specificity. D-Glucose, D-galactose, maltose, maltitol, and 1,4-butandiol were the most effective acceptors in the transgalactosylation catalyzed by this enzyme. The enzyme could also transfer alpha-galactosyl residues to pentoses (L-arabinose, D-xylose, and D-ribose) and methyl pentoses (D-fucose and L-rhamnose). The main transfer products to lactose, maltose, and sucrose as acceptors were identified as O-alpha-D-galactosyl-(1,6)-O-beta-D-galactosyl-(1,4)-D-glucose, O-alpha-D-galactosyl-(1,6)-O-alpha-D-glucosyl-(1,4)-D-glucose, and O-alpha-D-galactosyl-(1,6)-O-alpha-D-glucosyl-(1,2)-beta-D-fructoside (raffinose), respectively.

Candida↗
PubMed1986

Carbohydrate and protein contents of grain dusts in relation to dust morphology.

Grain dusts contain a variety of materials which are potentially hazardous to the health of workers in the grain industry. Because the characterization of grain dusts is incomplete, we are defining the botanical, chemical, and microbial contents of several grain dusts collected from grain elevators in the Duluth-Superior regions of the U.S. Here, we report certain of the carbohydrate and protein contents of dusts in relation to dust morphology. Examination of the gross morphologies of the dusts revealed that, except for corn, each dust contained either husk or pericarp (seed coat in the case of flax) fragments in addition to respirable particles. When viewed with the light microscope, the fragments appeared as elongated, pointed structures. The possibility that certain of the fragments within corn, settled, and spring wheat were derived from cell walls was suggested by the detection of pentoses following colorimetric assay of neutralized 2 N trifluoroacetic acid hydrolyzates of these dusts. The presence of pentoses together with the occurrence of proteins within water washings of grain dusts suggests that glycoproteins may be present within the dusts. With scanning electron microscopy, each dust was found to consist of a distinct assortment of particles in addition to respirable particles. Small husk fragments and "trichome-like" objects were common to all but corn dust.

Amino Acids↗
PubMed2003

D-Xylose transport by Candida succiphila and Kluyveromyces marxianus.

The kinetics and regulation of D-xylose uptake were investigated in the efficient pentose fermentor Candida succiphila, and in Kluyveromyces marxianus, which assimilate but do not ferment pentose sugars. Active high affinity (Km approximately 3.8 mM; Vmax approximately 15 nmol/[mg min]) and putative facilitated diffusion low-affinity (Km approximately 140 mM; Vmax approximately 130 nmol/[mg min]) transport activities were found in C. succiphila grown, respectively, on xylose or glucose. K. marxianus showed facilitated diffusion low-affinity (Km approximately 103 mM; Vmax approximately 190 nmol/[mg min]) transport activity when grown on xylose under microaerobic conditions, and both a low-affinity and an active high-affinity (Km approximately 0.2 mM; Vmax approximately 10 nmol/[mg min]) transport activity when grown on xylose under fully aerobic conditions.

Aerobiosis↗
PubMed2003

Cellulosic fuel ethanol: alternative fermentation process designs with wild-type and recombinant Zymomonas mobilis.

Iogen (Canada) is a major manufacturer of industrial cellulase and hemicellulase enzymes for the textile, pulp and paper, and poultry feed industries. Iogen has recently constructed a 40 t/d biomass-to-ethanol demonstration plant adjacent to its enzyme production facility. The integration of enzyme and ethanol plants results in significant reduction in production costs and offers an alternative use for the sugars generated during biomass conversion. Iogen has partnered with the University of Toronto to test the fermentation performance characteristics of metabolically engineered Zymomonas mobilis created at the National Renewable Energy Laboratory. This study focused on strain AX101, a xylose- and arabinose-fermenting stable genomic integrant that lacks the selection marker gene for antibiotic resistance. The "Iogen Process" for biomass depolymerization consists of a dilute-sulpfuric acid-catalyzed steam explosion, followed by enzymatic hydrolysis. This work examined two process design options for fermentation, first, continuous cofermentation of C5 and C6 sugars by Zm AX101, and second, separate continuous fermentations of prehydrolysate by Zm AX101 and cellulose hydrolysate by either wildtype Z. mobilis ZM4 or an industrial yeast commonly used in the production of fuel ethanol from corn. Iogen uses a proprietary process for conditioning the prehydrolysate to reduce the level of inhibitory acetic acid to at least 2.5 g/L. The pH was controlled at 5.5 and 5.0 for Zymomonas and yeast fermentations, respectively. Neither 2.5 g/L of acetic acid nor the presence of pentose sugars (C6:C5 = 2:1) appreciably affected the high-performance glucose fermentation of wild-type Z. mobilis ZM4. By contrast, 2.5 g/L of acetic acid significantly reduced the rate of pentose fermentation by strain AX101. For single-stage continuous fermentation of pure sugar synthetic cellulose hydrolysate (60 g/L of glucose), wild-type Zymomonas exhibited a four-fold higher volumetric productivity compared with industrial yeast. Low levels of acetic acid stimulated yeast ethanol productivity. The glucose-to-ethanol conversion efficiency for Zm and yeast was 96 and 84%, respectively.

Animal Feed↗
PubMed2006

Transcription analysis of recombinant saccharomyces cerevisiae reveals novel responses to xylose.

Lignocellulosic biomass, rich in hexose and pentose sugars, is an attractive resource for commercially viable bioethanol production. Saccharomyces cerevisiae efficiently ferments hexoses but is naturally unable to utilize pentoses. Metabolic engineering of this yeast has resulted in strains capable of xylose utilization. However, even the best recombinant S. cerevisiae strains of today metabolize xylose with a low rate compared to glucose. This study compares the transcript profiles of an S. cerevisiae strain engineered to utilize xylose via the xylose reductase-xylitol dehydrogenase pathway in aerobic chemostat cultures with glucose or xylose as the main carbon source. Compared to the glucose culture, 125 genes were upregulated, whereas 100 genes were downregulated in the xylose culture. A number of genes encoding enzymes capable of nicotinamide adenine dinucleotide phosphate regeneration were upregulated in the xylose culture. Furthermore, xylose provoked increased activities of the pathways of acetyl-CoA synthesis and sterol biosynthesis. Notably, our results suggest that cells metabolizing xylose are not in a completely repressed or in a derepressed state either, indicating that xylose was recognized neither as a fermentable nor as a respirative carbon source. In addition, a considerable number of the changes observed in the gene expression between glucose and xylose samples were closely related to the starvation response.

Acetyl-CoA Carboxylase↗
PubMed2002

Characterization of heterologous and native enzyme activity profiles in metabolically engineered Zymomonas mobilis strains during batch fermentation of glucose and xylose mixtures.

Zymomonas mobilis has been metabolically engineered to broaden its substrate utilization range to include D-xylose and L-arabinose. Both genomically integrated and plasmid-bearing Z. mobilis strains that are capable of fermenting the pentose D-xylose have been created by incorporating four genes: two genes encoding xylose utilization metabolic enzymes (xylA/xylB) and two genes encoding pentose phosphate pathway enzymes (talB/tktA). We have characterized the activities of the four newly introduced enzymes for xylose metabolism, along with those of three native glycolytic enzymes, in two different xylose-fermenting Z. mobilis strains. These strains were grown on glucose-xylose mixtures in computer-controlled fermentors. Samples were collected and analyzed to determine extracellular metabolite concentrations as well as the activities of several intracellular enzymes in the xylose and glucose uptake and catabolism pathways. These measurements provide new insights on the possible bottlenecks in the engineered metabolic pathways and suggest methods for further improving the efficiency of xylose fermentation.

Acetates↗
PubMed1975

Metabolism in normal and virus-transformed chick embryo fibroblasts as observed with glucose labeled with 14C and tritium and with tritium-labeled water.

Glucose metabolism in normal and virus-transformed chick embryo fibroblast cells in culture was observed by allowing the cells to metabolize [U-14C]glucose plus glucose labeled with tritium in the C-1, C-3, and C-6 positions. Similarities and differences between normal and transformed cells were observed and measured. Both normal and transformed cells are found to metabolize about 20% of the glucose via the oxidative pentose phosphate cycle, with the rates being about twice as much for transformed cells as for normal cells under the chosen conditions. Nevertheless, the ratio of glucose metabolized via oxidative pentose cycle to the net flow of that metabolized directly to fructose 6-phosphate is about the same in normal and transformed cells. Although the rate of flow of [14C]glucose into the tricarboxylic acid cycle intermediates and amino acids derived from them appears to be the same in normal and transformed cells, the rate of tritium incorporation from H3HO into these intermediates seems to be much higher in normal cells.

Animals↗
PubMedDate not supplied

Studies on the biosynthesis of striatal-type diterpenoids and the biological activity of herical.

Feeding experiments with specifically 13C-labeled glucose disclosed that the diterpenoid part of the striatals/striatins is formed via the mevalonate pathway, whereas the pentose moiety originates either via glucuronic acid (70%) or the pentose phosphate cycle (30%). Application of radioactively labeled herical to cultures of Hericium ramosum demonstrates the pivotal role of this cyathane-xyloside in striatal biosynthesis. Herical inhibits a large spectrum of fungi and bacteria and shows cytotoxic and hemolytic properties.

Anti-Bacterial Agents↗
PubMed1980

The effect of serum from obese and normal weight men on glucose metabolism in leucocytes.

The influence of pooled serum from either obese or normal weight males on glucose metabolism in human leucocytes has been studied. Leucocytes from normal weight males were incubated with 10-90% pooled serum and either [U-14C], or [1-14C]glucose. Compared to serum from the normal weight males, serum from the obese group had a more stimulating effect on the 14CO2 and [14C]lactate production from [U-14C]glucose and on the 14CO2 production from [1-14C]glucose. The two serum pools had the same stimulating effect on the Embden-Meyerhof pathway as indicated by the formation of [14C]lactate from [1-14C]glucose. Calculations revealed that the activity in the pentose phosphate pathway was stimulated more by serum from obese, than from normal weight males. It is a possibility that increased stimulation of the pentose phosphate pathway may contribute to the development of overweight.

Adolescent↗
PubMed1983

Glucose metabolism in the female rat adipocyte: lipid synthesis from glucose during pregnancy and progesterone treatment.

Pregnancy and progesterone treatment of ovariectomized rats decrease glucose metabolism through the pentose-phosphate pathway in isolated female rat adipocytes. As demonstrated in previous studies, progesterone directly decreases [1-14C]glucose oxidation through the pentose-phosphate pathway and lipogenesis from [6-14C]glucose, the present study therefore compared glucose-induced lipid synthesis during pregnancy (10, 16 and 20 days of pregnancy) with the effect of progesterone treatment (5 mg/rat per day for 14 days) to shed more light on the role of this steroid in glucose metabolism during pregnancy. The inhibition of [6-14C]glucose incorporation into triacylglycerols in the progesterone-treated rats was comparable to that which occurs during late (20 days) and mid-pregnancy (16 days) but not during early pregnancy (10 days). The inhibition of fatty acid synthesis was more important as pregnancy advanced and was different from the decrease in fatty acid synthesis induced by progesterone treatment. The sensitivity to insulin was comparable in virgin, ovariectomized and progesterone-treated ovariectomized rats but not in pregnant rats. This implies that progesterone and insulin affect glucose-induced lipid synthesis by distinct processes and that the impaired glucose metabolism is characterized by a reduction in basal glucose utilization rather than by an impaired insulin response.

Adipose Tissue↗
PubMed1976

Effect of adrenalectomy on rat mammary metabolism.

Rates and patterns of metabolism of specifically labeled glucose, pyruvate, and acetate by mammary slices indicated that rates of glucose metabolism through the Embden-Meyerhof and pentose phosphate pathways and relative pentose cycle activity were decreased by adrenalectomy. Fatty acid synthesis from acetate was not impaired. Capacity to provide reduced nicotinamide adenine dinucleotide phosphate for fatty acid synthesis was not the limiting factor responsible for decreased fatty acid synthesis from glucose in adrenalectomized, lactating rat mammary glands. Oxidation of [1-carbon-14]pyruvate and fatty acid synthesis from [2-carbon-14] pyruvate were not affected by adrenalectomy. Indirect reasoning based upon the data reported led to the suggestion that decreased fatty acid synthesis from glucose after adrenalectomy may have resulted from decreased formation of triose phosphate via the phosphofructose-kinase reaction. It is suggested further that most of the decreases in rat mammary enzyme after adrenalectomy have no direct (causative) relationship to depressed lactational performance after adrenalectomy. Restriction of food intake caused decreased fatty acid synthesis from glucose, pyruvate, and acetate, but relative fatty acid esterification activity was higher than in control and adrenalectomized animals. The effects of adrenalectomy on mammary gland metabolism can be dissociated partially from reduced food intake.

Acetates↗
PubMed1986

Effects of age, milk replacer composition, and rumen function on lipogenesis in adipose tissue of young calves.

Rates of utilization of glucose, acetate, and lactate and activities of selected enzymes were determined in vitro to evaluate the effects of age and diet on lipogenesis in perirenal adipose tissue of calves. Three-day-old Holstein bull calves were fed up to 12 wk of age on one of three dietary treatments: a high carbohydrate milk replacer; a high fat milk replacer; and weaning at 6 wk of age from high fat replacer to calf starter. Adipose tissue biopsies were obtained from calves at 2, 5, 8, and 12 wk of age. Rates of fatty acid synthesis and activities of enzymes of the pentose phosphate and citrate cleavage pathways were increased in calves fed high carbohydrate milk replacer. These parameters were decreased in calves fed high fat replacer and were further depressed after weaning. Substrate preference for fatty acid synthesis in all calves was acetate, then lactate, then glucose. With increase in age from 2 to 12 wk, adipose tissue of calves fed milk replacer partitioned more acetate and lactate toward fatty acid synthesis and less toward oxidation. The pentose phosphate cycle was characterized by high rate of recycling and contributed at least 50% of reducing equivalents required for fatty acid synthesis. It appeared that several features of lipogenesis characteristic of functional ruminants are also shared by preruminant calves.

Adipose Tissue↗
PubMed2026

Xy-31 and Lat-1 regulate the induction of polysaccharide disintegrating genes by arabinose in Neurospora crassa OR74A.

BACKGROUND: Arabinose has been identified as a potent inducer of the cellulase regulon in filamentous fungi. However, the precise molecular mechanisms that drive this induction remain largely unknown. This study aimed to elucidate the mechanisms underlying the arabinose-induced activation of cellulase and hemicellulase enzyme clusters in the model filamentous fungus Neurospora crassa OR74A. RESULTS: Arabinose stimulates the secretion of cellulases and hemicellulases in N. crassa. While genome-wide scrutiny predicted several sugar transporters in N. crassa, expression studies under avicel and arabinan conditions indicated a notable upregulation of pentose transporters encoded by the lat-1 and xy-31 genes. The lat-1 and xy-31 deleted strains showed reduced arabinose uptake and diminished growth on arabinose media, highlighting their role in arabinose transport. Additionally, these transporter-deficient strains exhibited a significant decrease in endoglucanase and arabinase activity, which correlated with lower expression of cellulase-encoding transcripts, indicating the crucial roles of Lat-1 and Xy-31 in promoting the secretion of enzymes that degrade biomass. Consistent with these findings, overexpression of lat-1 and xy-31 in N. crassa resulted in a significant increase in cellulase secretion. CONCLUSION: We demonstrated that N. crassa has multiple pentose transporters. Furthermore, we validated that the Lat-1 and Xy-31 transporters play crucial roles in arabinose-mediated induction of polysaccharide-disintegrating enzymes in N. crassa. Both transporters are required for efficient arabinose uptake and for the subsequent arabinose-dependent induction of polysaccharide-disintegrating enzymes. Collectively, these findings significantly advance the molecular understanding of fungal hemicellulose utilization and identify key transporters that represent promising targets for enhancing fungal biomass bioconversion.

arabinose↗
PubMed1976

[Use of glucose-6-phosphate dehydrogenase and transketolase for characterization of pathologic processes in the myocardium in rheumatism].

In patients with active rheumatism the activity of the key enzymes of the pentose cycle -- glucoso-6-phosphatedehydrogenase and transketolase -- increases in the erythrocytes of the peripheral blood parallel with the severity of the inflammatory lesion of the heart. In patients with distrophic changes in the myocardium without concomitant carditis the level of glucoso-6-phosphatedehydrogenase did not change significantly, while the content of transketolase decreased considerably. Antirheumatic therapy helping to reduce the inflammatory reactions in the heart results in a reduction of the level of pentose cycle enzymes. The study of the ratio between glucoso-6-phosphatedehydrogenase and transketolase may prove valuable for an approximate evaluation of the predominance of inflammatory or dystrophic processes in the cardiac muscle.

Adolescent↗
PubMedDate not supplied

[Effect of hydrocortisone acetate on carbohydrate metabolism and cellular respiration of lymphoma NK/ly].

Hydrocortisone acetate caused the inhibition of the limphoma cells growing. In the process the aerobic glycolysis was increased, the respiratory activity was altered slightly but the magnitude of Crebtry effect was distinctly decreased. Under effect of the hormone the activity of pentose pathway was drastically increased: oxidation via 6-phosphogluconate and the synthesis of phosphorylated carbohydrates by "non-oxidative" pathway were increased 1.7- and 7.4-fold, respectively. Thus, the stopping of the tumor cells development occurred with simultaneous activation of the pentose-phosphate pathway and energy metabolism as a whole.

Animals↗