Diabetes and mitochondrial bioenergetics: alterations with age

Several studies have been carried out to evaluate the alterations in mitochondrial functions of diabetic rats. However, some of the results reported are controversial, since experimental conditions, such as aging, and/or strain of animals used were different. The purpose of this study was to evaluate the metabolic changes in liver mitochondria, both in the presence of severe hyperglycaemia (STZ-treated rats) and mild hyperglycaemia (Goto-Kakizaki (GK) rats). Moreover, metabolic alterations were evaluated both at initial and at advanced states of the disease. We observed that both models of type 1 and type 2 diabetes presented alterations on respiratory chain activity. Because of continual severe hyperglycaemia, 9 weeks after the induction of diabetes, the respiratory function declined in STZ-treated rats, as observed by membrane potential and respiratory ratios (RCR, P/O, and FCCP-stimulated respiration) assessment. In contrast, GK rats of 6 months age presented increased respiratory ratios. To localize which respiratory complexes are affected by diabetes, enzymatic respiratory chain activities were evaluated. We observed that succinate dehydrogenase and cytochrome c oxidase activities were significantly augmented both in STZ-treated rats and GK rats of 6 months age. Moreover, H(+)-ATPase activity was also significantly increased in STZ-treated rats with 3 weeks of diabetes and in GK rats of 6 months age as compared to controls. Therefore, these results clearly suggest that both animal models of diabetes present some metabolic adjustments in order to circumvent the deleterious effects promoted by the high glucose levels typical of the disease.     

Energy requirements of the red kangaroo (<Emphasis Type="Italic">Macropus rufus</Emphasis>): impacts of age,growth and body size in a large desert-dwelling herbivore.

Generally, young growing mammals have resting metabolic rates (RMRs) that are proportionally greater than those of adult animals. This is seen in the red kangaroo (Macropus rufus), a large (>20 kg) herbivorous marsupial common to arid and semi-arid inland Australia. Juvenile red kangaroos have RMRs 1.5–1.6 times those expected for adult marsupials of an equivalent body mass. When fed high-quality chopped lucerne hay, young-at-foot (YAF) kangaroos, which have permanently left the mother's pouch but are still sucking, and recently weaned red kangaroos had digestible energy intakes of 641±27 kJ kg^–0.75 day^–1 and 677±26 kJ kg^–0.75 day^–1, respectively, significantly higher than the 385±37 kJ kg^–0.75 day^–1 ingested by mature, non-lactating females. However, YAF and weaned red kangaroos had maintenance energy requirements (MERs) that were not significantly higher than those of mature, non-lactating females, the values ranging between 384 kJ kg^–0.75 day^–1 and 390 kJ kg^–0.75 day^–1 digestible energy. Importantly, the MER of mature female red kangaroos was 84% of that previously reported for similarly sized, but still growing, male red kangaroos. Growth was the main factor affecting the proportionally higher energy requirements of the juvenile red kangaroos relative to non-reproductive mature females. On a good quality diet, juvenile red kangaroos from permanent pouch exit until shortly after weaning (ca. 220–400 days) had average growth rates of 55 g body mass day^–1. At this level of growth, juveniles had total daily digestible energy requirements (i.e. MER plus growth energy requirements) that were 1.7–1.8 times the MER of mature, non-reproductive females. Our data suggest that the proportionally higher RMR of juvenile red kangaroos is largely explained by the additional energy needed for growth. Energy contents of the tissue gained by the YAF and weaned red kangaroos during growth were estimated to be 5.3 kJ g^–1, within the range found for most young growing mammals.Abbreviations BMR basal metabolic rate - DEI digestible energy intake - MER maintenance energy requirement - MER_g maintenance plus growth energy requirement - PPE permanent pouch exit - RMR resting metabolic rate - YAF young-at-foot Communicated by I.D. Hume     

Coumarin inhibits the growth of carrot (Daucus carota L. cv. Saint Valery) cells in suspension culture

We used a carrot (Daucus carota L. cv. Saint Valery) cell suspension culture as a simplified model system to study the effects of the allelochemical compound coumarin (1,2 benzopyrone) on cell growth and utilisation of exogenous nitrate, ammonium and carbohydrates. Exposure to micromolar levels of coumarin caused severe inhibition of cell growth starting from the second day of culture onwards. At the same time, the presence of 50 mumol/L coumarin caused accumulation of free amino acids and of ammonium in the cultured cells, and stimulated their glutamine synthetase, glutamate dehydrogenase, glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxylase activities. Malate dehydrogenase, on the other hand, was inhibited under the same conditions. These effects were interpreted in terms of the stimulation of protein catabolism and/or interference with protein biosynthesis induced by coumarin. This could have led to a series of compensatory changes in the activities of enzymes linking nitrogen and carbon metabolism. Because coumarin seemed to abolish the exponential phase and to accelerate the onset of the stationary phase of cell growth, we hypothesise that such allelochemical compounds may act in nature as an inhibitor of the cell cycle and/or as a senescence-promoting substance.     

Systemic induction of the biosynthesis of terpenic compounds in Digitalis lanata

A bacterial screening was carried out in the rhizosphere of two Digitalis species, D. thapsi and D. parviflora, both at the vegetative stage and at flowering. A total of 480 isolates were characterised at genus level, Bacillus being the dominant genera in all cases. Fifty percent of the Bacillus strains isolated from each species were analysed by PCR-RAPDs. At 85% similarity, 12 groups separated for D. thapsi and 18 for D. parviflora. One strain of each group was selected for biological assay on D. lanata, evaluating growth promotion and cardenolide content in leaves after inoculation performed in the root system. The plant parameters evaluated were leaf surface area, shoot and root dry weight and leaf number. Lanatoside C content was evaluated by HPLC. Only 17 strains caused significant increases in at least one of the parameters evaluated. The most striking result was that some strains promoted growth and increased cardenolide content at the same time. This effect was detected on leaves while inoculation was carried out on roots. Interestingly, these two parameters are not enhanced simultaneously under regular conditions in pot or in tissue cultures.     

Photosynthetic flexibility in Pedilanthus tithymaloides poit,a CAM plant

The induction of CAM in Pedilanthus tithymaloides (Euphorbiaceae) under water-limited conditions was evaluated by following diurnal oscillations of CO2 fixation, titratable acidity and malic acid content in the leaf extracts. CAM induction was assessed by measuring the activities of phosphoenolpyruvate carboxylase (PEPC), NADH-malate dehydrogenase (MDH) and phosphoenolpyruvate caroxykinase (PEPCK) in the leaves as well. Drought resulted in large increases in the nocturnal acid accumulation and rates of CO2 uptake in the leaves of P. tithymaloides. The drought-induced CAM activity tended to be reversible after re-watering. Nevertheless, under well-watered conditions, plants of P. tithymaloides showed day time CO2 uptake patterns with less pronounced diurnal oscillations of organic acids. Our data indicate that although P. tithymaloides is a CAM plant, environmental variables like drought induce photosynthetic flexibility in this species. This type of plasticity in CAM and metabolic versatility in P. tithymaloides should be an adaptation for prolonged survival under natural adverse edaphic and microclimate situations.     

LmbJ and LmbIH protein levels correlate with lincomycin production in Streptomyces lincolnensis

AIMS: To demonstrate the expression of two overlapping genes lmbJ and lmbIH in Streptomyces lincolnensis and to document LmbJ and LmbIH protein levels during the lincomycin production phase. To analyse presumable function of the LmbIH protein. METHODS AND RESULTS: Lincomycin production was monitored by thin-layer chromatography, proteins LmbJ and LmbIH were assayed in the cell-free extracts of S. lincolnensis by immunodetection. LmbJ occurred at stable level (2-4 mg x g(-1) of total proteins) for a long time period (36-96 h of cultivation) covering the whole production phase. This fairly corresponds to the catalytic function of the protein in the antibiotic biosynthesis (N-demethyllincomycin methyltransferase). On the contrary, LmbIH reached the detectable level (0.1 and 0.7 mg x g(-1)) just for a short period at 60-72 h. CONCLUSIONS: The absence of LmbIH protein at a detectable level during the major part of the antibiotic production phase casts doubt on its possible catalytic function. Rather a different connection with the final biosynthetic steps, e.g. regulatory, can be envisaged. SIGNIFICANCE AND IMPACT OF THE STUDY: Expression of a newly found putative regulatory gene was demonstrated during production of industrial antibiotic, lincomycin.     

Cloning,characterization and chromosomal localization of the Sus scrofa SLC31A1 gene

Copper is an essential element necessary for normal function of numerous enzymes in all living organisms. Uptake of copper into the cell is thought to occur through the membrane protein, SLC31A1 (CTR1), which has been described in a variety of species including yeast, human and mouse. In this study, we present cloning, gene structure, chromosomal localization and expression pattern of the Sus scrofa SLC31A1 gene, which encodes a 189 amino acid protein. The (SSC) SLC31A1 gene is organized in four exons and spans an approximately 2.3 kb genomic region. We have localized the gene to chromosome 1q28-q2.13 using a somatic cell hybrid panel. This region shows conservation of synteny with human chromosome 9, where the human SLC31A1 (CTR1) gene has been localized. Expression studies suggest that SLC31A1 mRNA is transcribed in all tissues examined.     

Production of gamma-linolenic acid by disrupted mycelia of Mortierella isabellina

AIMS: To optimize the production of linolenic acid by disrupted mycelia of Mortierella isabellina. METHODS AND RESULTS: Effects of incubation conditions such as incubation time, pH of reaction mixture, concentration of Mg2+ or malate and incubation temperature on production of linolenic acid were studied. The production of gamma-linolenic acid reached 224 mg g-1 dry cells when the reaction mixture was composed of 1.0 g (dry mycelial mass) of disrupted mycelia of M. isabellina, 50 ml (50 mmol l(-1)) potassium phosphate buffer supplemented with 0.312 mmol l(-1) of Mg2+ and 10 mmol l(-1) of malate, pH 7.0 and incubated at 5 degrees C for 1 day. CONCLUSIONS: Incubation temperature, concentration of Mg2+ and malate showed major effects on the increased linolenic acid production. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlights conditions for increasing gamma-linolenic acid production by cell-free mycelia of M. isabellina and an insight into rapidly gaining high production of polyunsaturated fatty acids.