Control of lactate production by Selenomonas ruminantium: homotropic activation of lactate dehydrogenase by pyruvate.

Selenomonas ruminantium produced one mole of D(-)-lactate per mole of glucose used at all dilution rates in ammonia-limited continuous culture. In contrast, lactate production varied according to the dilution rate when glucose was the limiting nutrient. At dilution rates of less than 0.2 h-1, acetate and propionate were the main fermentation products and lactate production was low. At dilution rates above 0.2 h-1, the pattern changed to one of high lactate production similar to that under ammonia limitation. Experiments with cell-free extracts of S. ruminantium showed that D(-)-lactate dehydrogenase had sigmoidal kinetics consistent with homotropic activation of the enzyme by its substrate, pyruvate. This feature allows S. ruminantium to amplify the effects of relatively small changes in the intracellular concentration of pyruvate to cause much larger changes in the rate of production of lactate. Some confirmation that this mechanism of control occurs under physiological conditions was obtained in glucose-limited culture, in which the sigmoidal increase in lactate production was accompanied by a linear increase in pyruvate excretion as the dilution rate increased.     

Metabolism of aminoacyl-p-nitroanilides by rat mammary tissue

We have examined the metabolism of aminoacyl-p-nitroanilides by rat mammary tissue isolated from rats during late pregnancy, peak lactation and late lactation. The rate of hydrolysis depended upon the chemical nature of the aminoacyl-p-nitroanilide compound and the physiological state of the donor animals. Thus, mammary tissue isolated from rats during late pregnancy and peak lactation hydrolysed aminoacyl-p-nitroanilides in the order L-met-p-nitroanilide=L-leu-p-nitroanilide>L-lys-p-nitroanilide>gamma- glu-p-nitroanilide. The order of activity was the same for mammary tissue taken from rats during late lactation except that L-lys-p-nitroanilide was hydrolysed at the same rate as the neutral aminoacyl-p-nitroanilides. Mammary tissue from peak lactating rats also hydrolysed alpha-L-glu-p-nitroanilide and alpha-L-asp-p-nitroanilide but to a lesser extent than the other compounds tested. The anionic aminoacyl-p-nitroanilides were able to trans-stimulate D-aspartate efflux from mammary tissue explants and the perfused mammary gland via the high-affinity anionic amino acid carrier. The clearance of gly-L-phe by the perfused mammary gland was markedly inhibited by L-phe. The results suggest that mammary tissue expresses a variety of dipeptidases at the basolateral aspect of the mammary epithelium which are capable of hydrolysing peptides extracellularly. These enzymes may be important for providing amino acids for milk protein synthesis and/or inactivating signal peptides.     

Glutathione utilization by lactating bovine mammary secretory tissue in vitro.

gamma-Glutamyltransferase (D-glutamyl transpeptidase, EC 2.3.2.2) activity has been shown to be located predominantly on the extracellular surface of the plasma membrane of lactating bovine mammary cells. Radioactive label from both oxidized ([14C]-gamma-glutamyl) and reduced ([35S]cysteinyl) glutathione was taken up and incorporated into acid-precipitable proteins of mammary tissue. Uptake was shown to involve the transport of free amino acids, and incorporation was shown to involve the action of gamma-=glutamyltransferase. These results indicate that lactating mammary tissue utilizes the constituent amino acids of glutathione for milk-protein synthesis.     

Aerobic exercise attenuates inducible TNF production in humans.

Aerobic exercise reduces coronary heart disease risk, but the mechanisms of this protection are not fully understood. Atherosclerosis is an inflammatory disease mediated by monocyte-derived macrophages, which accumulate in arterial plaques and become activated to release factors, including cytokines, that cause damage. Here we studied the effects of aerobic training on monocyte production of tumor necrosis factor (TNF) in whole blood ex vivo. Healthy young sedentary adults (n = 61, age 20-45 yr) were randomized to a moderate- (M) or a high- (H) intensity 12-wk training program. Whole blood was extracted before and after training, and then it was stimulated by addition of lipopolysaccharide (LPS); inducible TNF was measured in the plasma. Data were analyzed according to intention to treat principles using a random-effect model to determine the impact of training group on maximal aerobic capacity and LPS-stimulated TNF after correcting for covariates. Analyses revealed improvement in aerobic capacity in both the H (9%) and the M (7%) groups. However, aerobic training led to significant (P < 0.001) decreases in TNF release only in the H group. These data suggest that in healthy young adults, a 12-wk high-intensity aerobic training program downregulates blood monocyte production of stimulated cytokine release.     

Sodium lactate delays toxin production by Clostridium botulinum in cook-in-bag turkey products.

Comminuted raw turkey, containing 1.4% sodium chloride, 0.3% sodium phosphate, and 0 (control), 2.0, 2.5, 3.0, or 3.5% sodium lactate, was inoculated with a 10-strain mixture of proteolytic type A and B Clostridium botulinum spores. The inoculated turkey was vacuum packaged and cooked by immersion in heated water to an internal temperature of 71.1 degrees C. Samples were incubated at 27 degrees C for up to 10 days. Five samples per treatment were examined for botulinal toxin at specific intervals. Sodium lactate exhibited an antibotulinal effect which was concentration dependent. Processed turkey containing 0, 2.0, 2.5, 3.0, or 3.5% sodium lactate was toxic after 3, 4 to 5, 4 to 6, 7 or 7 to 8 days, respectively. Subsequent studies with a broth medium revealed that lactate, not the sodium ion, was the principal factor in delaying botulinal-toxin formation.     

Possibility of enzymatic lactate disintegration followed by formate production

A possibility of lactate reverse desintegration to formate and acetaldehyde by lactate-synthase was established by the methods of enzymatic analysis, isotope indication, thin layer chromatography.     

Parathyroid hormone-related protein production by primary cultures of mammary epithelial cells.

Parathyroid hormone-related protein (PTHrP) plays a major role in the pathogenesis of malignant hypercalcemia, but has also been found in fetal and adult non-neoplastic tissues. Among them, lactating mammary gland was shown to produce PTHrP, and high levels of PTHrP were measured in milk. However, the regulation of PTHrP production by breast cells is still unknown. Primary cultures of mammary cells isolated from rat lactating glands were grown on collagen gels in an insulin/epidermal growth factor (EGF)-supplemented medium. Under these conditions, mammary cells displayed an epithelial phenotype and their number increased more than twofold after 1 week in culture. At that time, the cells were capable of producing immunoreactive PTHrP (range: 25 to 150 pg/10(5) cells x 24 h) and PTH-like bioactivity, as indicated by a 60% increase in cyclic adenosine monophosphate (cAMP) production induced by mammary epithelial cell conditioned medium in the PTH-responsive osteoblast-like UMR-106 cell line. When cell proliferation was hindered by lowering plating density, by removing medium supplements, or by adding transforming growth factor (TGF)-beta, a well-known autocrine inhibitor of mammary epithelial cell growth. PTHrP production was increased. In contrast, the omission of EGF or addition of specified anti-EGF antibodies decreased PTHrP production. In conclusion, primary cultures of mammary epithelial cells isolated from lactating rat were shown for the first time to produce PTHrP in vitro. This production was higher in the presence of EGF and could be modulated by cell growth rate.     

Aerobic hydrogen production by the heterocystous cyanobacteria Anabaena spp. strains CA and 1F.

Aerobic photoproduction of H2 was demonstrated in Anabaena spp. strains CA and 1F when cells were growing under nitrogen-fixing conditions. The rates of production, measured either by the hydrogen electrode or in a flow system by gas chromatography, were 10 to 15% of the rate of photosynthetic O2 evolution or 50 to 80% of the rates of acetylene reduction. Strains CA and 1F differed in several respects. In strain CA, H2 production was immediately partially sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, whereas strain 1F was not immediately affected. Strain CA also showed a consistently higher rate of H2 production than did strain 1F. H2 production in strain CA was also markedly influenced by the light intensity used for growth, although the growth rates indicated that the light intensities used were essentially saturating.     

gamma-Glutamyl transpeptidase in rat mammary tissue. Activity during lactogenesis and regulation by prolactin.

The increased activity of gamma-glutamyl transpeptidase (EC 2.3.2.2) in rat mammary tissue at the onset of lactation was shown to involve prolactin. The timing and magnitude of these changes and its prolactin requirement suggest an important role in mammary function.     

Acetate production from lactate and glucose fermentation by Gluconobacter oxydans

Summary The production of acetate from the fermentation of lactate by Gluconobacter oxydans was studied. Batch experiments showed that glucose was the preferred substrate compared to lactate. A fed-batch culture was fed with a mixture of glucose and lactate followed by periodic addition of lactate. The maximum productivity of acetate was 0.16 g/l h but this value decreased during the fedbatch culture due to growth inhibition by acetate.