Isolation and characterization of a new bacteriochlorophyll-c bearing a neopentyl substituent at the 8-position from the bciD-deletion mutant of the brown-colored green sulfur bacterium Chlorobaculum limnaeum

We recently constructed the mutant of the brown-colored green sulfur bacterium Chlorobaculum limnaeum lacking BciD which was responsible for formation of a formyl group at the 7-position in bacteriochlorophyll(BChl)-e biosynthesis. This mutant exclusively gave BChl-c, but not BChl-e, as the chlorosome pigments (Harada et al. in PLoS One 8(4):e60026, 2013). By the mutation, the homolog and epimer composition of the pigment was drastically altered. The methylation at the 8²-position in the mutant cells proceeded to create BChl-c carrying large alkyl substituents at this position. Correspondingly, the content of BChls-c having the (S)-configuration at the chiral 3¹-position remarkably increased and accounted for 80.6 % of the total BChl-c. Based on the alteration of the pigment composition in the mutant cells, a new BChl-c bearing the bulkiest, triple 8²-methylated neopentyl substituent at the 8-position ([N,E]BChl-c) was identified. The molecular structure of [N,E]BChl-c was fully determined by its NMR, mass, and circular dichroism spectra. The newly identified [N,E]BChl-c was epimerically pure at the chiral 3¹-position and its stereochemistry was determined to be an (S)-configuration by modified Mosher’s method. Further, the effects of the C8²-methylation on the optical absorption properties of monomeric BChls-c were investigated. The Soret but not Qy absorption bands shifted to longer wavelengths by the extra methylation (at most 1.4 nm). The C8²-methylation induced a slight but apparent effect on absorption properties of BChls-c in their monomeric states.     

Peroxidase-like activities of iron(III)—Porphyrins: kinetics of the reduction of a peroxidatically active derivative of deuteroferriheme by anilines

The kinetics of the reduction by aniline and a series of substituted anilines of a peroxidatically active intermediate, formed by oxidation of deuteroferriheme with hydrogen peroxide, have been studied by stopped-flow spectrophotometry. The reaction with aniline was first order with respect to [intermediate] and showed first-order saturation kinetics with respect to [aniline]. The second-order rate constant was 2.0 ± 0.2 × 10⁵ M^?1 sec^?1 at 25°C (independent of pH in the range 6.60–9.68) compared with the value of 2.4 × 10⁵ M^?1 sec^?1 for the reaction of aniline with horseradish peroxidase Compound I. The effect of aniline substituents upon reactivity towards the heme intermediate closely paralled those reported for reaction with the enzymic intermediate. Anilines bearing electron-donating substituents reacted more rapidly and those bearing electron-withdrawing substituents more slowly than the unsubstituted amine. The rate constants for the heme intermediate reactions (k_dfh)found to be related to those for the enzymic reactions (k_hrp) by the equation:log k_DFH= 0.65log k_HRP+ 1.96 with a correlation coefficient of 0. 98.     

Effect of oxygen supply and dilution rate on the production of 2,3-butanediol in continuous bioreactor by Klebsiella pneumoniae

Kinetics of 2,3-butanediol production by Klebsiella pneumoniae (NRRL B199) from glucose have been studied in a continuous bioreactor. The effect of oxygen supply rate and dilution rate on the product output rate and yield of 2,3-butanediol were investigated. For a feed glucose concentration of 100 g l⁻¹, the optimum oxygen transfer rate is between 25.0–35.0 mmol l⁻¹ h⁻¹. Under these conditions, maximum product concentration obtained was 35 g l⁻¹ at a dilution rate of 0.1 h⁻¹ and the maximum product output rate obtained was 4.25 g l⁻¹ h⁻¹. The product yield based on the substrate utilized approached the theoretical value (50%) at low values of oxygen transfer rate but decreased with increasing oxygen transfer rate.     

Anti-biofilm potential of Lactobacillus plantarum Y3 culture and its cell-free supernatant against multidrug-resistant uropathogen Escherichia coli U12

Uropathogens develop biofilms on urinary catheters, resulting in persistent and chronic infections that are associated with resistance to antimicrobial therapy. Therefore, the current study was performed to control biofilm-associated urinary tract infections through assaying the anti-biofilm ability of lactic acid bacteria (LAB) against multidrug-resistant (MDR) uropathogens. Twenty LAB were obtained from pickles and fermented dairy products, and screened for their anti-biofilm and antimicrobial effects against MDR Escherichia coli U12 (ECU12). Lactobacillus plantarum Y3 (LPY3) ({"type":"entrez-nucleotide","attrs":{"text":"MT498405","term_id":"1843980272","term_text":"MT498405"}}MT498405), showed the highest inhibitory effect and biofilm production. Pre-coating of a microtitre plate with LPY3 culture was more potent than co-incubation. Pre-coating with LPY3 culture generated a higher anti-biofilm effect with an adherence of 14.5% than cell free supernatant (CFS) (31.2%). Anti-biofilm effect of CFS was heat stable up to 100 °C with higher effect at pH 4–6. Pre-coating urinary catheter with LPY3 culture reduced the CFU/cm² of ECU12 attached to the catheter for up to seven days. Meanwhile, CFS reduced the ECU12 CFU/cm² for up to four days. Scanning electron microscope confirmed the reduction of ECU12 adherence to catheters after treatment with CFS. Therefore, Lactobacillus plantarum can be applied in medical devices as prophylactic agent and as a natural biointervention to treat urinary tract infections.     

Mössbauer and spectroscopic studies on substituted tetraphenylporphyrinato iron(III) complexes in aqueous solutions and the formation of the μ-oxo-bridged species

Electronic and ⁵⁷Fe Mössbauer spectra are reported for two new water-soluble porphyrinato iron(III) complexes. Equilibrium constants for μ-oxo bishaem formation are calculated assuming two protons are released.Comparisons are made of the data with other porphyrinato iron(III) systems and it is shown that, in the absence of well-defined fifth ligands, the mononuclear species in acidic solution probably contain two axial water ligands. The μ-oxo bishaems do not contain water or hydroxide coordinated to iron but may hold water by hydrogen-bonding to the oxygen bridge or possibly by aquation of the porphyrin ligands.μ-Oxo bridge formation is controlled by the acid strength of the water coordinated to the iron in the mononuclear species, low pK_a values assisting oxo-bridge formation. Such low pK_a values are assisted by electron-attracting substituents on the porphyrin periphery. It is noted that this same property assists the stabilisation of iron(II) complexes. Steric inhibition of oxo-bridge formation requires large substituents, unsubstituted phenyl groups being apparently not large enough.     

Antimicrobial effects of new 1-(1,2,4-triazol-1-yl)-acetanilides

Fourteen synthetically prepared 1-(1,2,4-triazol-1-yl)acetanilides were tested for antimicrobial effect. None of the prepared derivatives influenced theB. subtilis, P. fluorescens nor the tested yeasts. Only the derivatives with substituents in positionspara orortho andpara were biologically effective. The widest antimicrobial spectrum was manifested by the pentachloro derivative, which was effective with G⁺ and G^? bacteria and with filamentous fungi.     

Nitrogen partitioning and isotopic discrimination are affected by age and dietary protein content in growing lambs

It is difficult to separate an age-dependent fall in nitrogen use efficiency (NUE; N balance/N intake) in growing ruminants from a progressively decrease in animal protein requirements over time. This study examined the effect of dietary protein content on N partitioning, digestibility and N isotopic discrimination between the animal and its diet (Δ¹⁵N_animal-diet) evaluated at two different fattening periods (early v. late). Twenty-four male Romane lambs (age: 19 ± 4.0 days; BW: 8.3 ± 1.39 kg) were equally allocated to three dietary CP treatments (15%, 17% and 20% CP on a DM basis). Lambs were reared with their mothers until weaning, thereafter housed in individual pens until slaughter (45 kg BW). During the post-weaning period, lambs were allocated twice (early fattening (30 days post-weaning) and late fattening (60 days post-weaning)) to metabolic cages for digestibility and N balance study. When diet CP content increased, the average daily gain of lambs increased (P < 0.05) while the age at slaughter decreased (P = 0.01), but no effect was observed on feed efficiency (P > 0.10). Diet CP content had limited effect on lamb carcass traits. Higher fibre digestibility was observed at the early v. late fattening period (P < 0.001). The N intake and the urinary N excretion increased when diet CP content increased (P < 0.001) and when shifting from early to late fattening period (P < 0.001). Faecal N excretion (P = 0.14) and N balance (P > 0.10) were not affected by diet CP content. Nitrogen digestibility increased (P < 0.001) as the diet CP content increased and on average it was greater at late v. early fattening period (P = 0.02). The NUE decreased (P = 0.001) as the diet CP content increased and as the lamb became older (P < 0.001). However, the age-dependent fall in NUE observed was lower at high v. low dietary CP content (CP × age interaction; P = 0.04). The Δ¹⁵N_animal-diet was positively correlated (P < 0.05) with N intake (r = 0.59), excretion of faecal N (r = 0.41), urinary N (r = 0.69) and total manure N (r = 0.64), while negatively correlated with NUE (r = −0.57). Overall, the experiment showed NUE was lower in older lambs and when lambs were fed high diet CP content, and that Δ¹⁵N_animal-diet was a useful indicator not only for NUE but also for urinary N excretion, which is a major environmental pollution factor on farm.     

Quantitative structure-activity relationship of cytokinin-active adenine and urea derivatives

The substituent effect of N⁶-alkyl and -aralkyl adenines on the promotion of the growth of tobacco callus was analysed quantitatively using physico-chemical substituent parameters and regression analysis. The results indicated an optimum steric condition for activity in terms of the maximum width of the N⁶-substituents from the bond-axis connecting the N⁶-atom with its α carbon atom. The electron withdrawing effect of the N⁶-substituent enhances the activity. The substituent effect on the cytokinin activity of phenyl- and diphenyl- urea derivatives determined by Bruce and Zwar using the tobacco pith-block assay was also analysed. The results suggest that position-specific steric and hydrophobic effects of aromatic substituents participate in the variation in activity rationalizing the general trend of the activity; meta >para >ortho derivatives, for both series of compounds. The electronic effect is significant for the activity of diphenylureas but not for that of phenylureas which show somewhat different modes of interaction between the two series at the site of action. Based on inferences made from the correlations, hypothetical maps for the mode of interaction of these three sets of compounds at the site of action have been proposed.     

Effect of Zinc Supplementation on Inflammatory Markers and Adipokines in Young Obese Women

Obesity is a chronic inflammatory state characterized by altered adipokine production and increased levels of inflammatory cytokines. The study explored the effect of zinc supplementation on inflammatory markers and adipocyte hormones in young obese women. Twenty five non-obese women and forty obese women (body mass index ≥25 kg/m²) aged 19–28 years were recruited for this study. Twenty obese women of the study group took 30 mg/day of supplemental zinc as zinc gluconate for 8 weeks and 20 obese women of control group took placebo. Usual dietary zinc intake was estimated from 3-day diet records. Serum zinc and urinary zinc concentration were measured by Atomic Absorption Spectrophotometry. Inflammatory markers such as high sensitivity C-reactive protein (hs-CRP), tumor necrosis factor-alpha (TNF-α), and interleukin (IL)-6 and adipocyte hormones such as lepin and adiponectin were measured by enzyme immunoassay. Inflammatory markers and leptin were significantly higher, but adiponectin was significantly lower in obese women than non-obese women. Zinc supplementation increased serum zinc by 15 % and urinary zinc by 56 % (P?<?0.05). The levels of hs-CRP (P?=?0.03) and IL-6 (P?=?0.006) significantly decreased with zinc supplementation, but not in placebo group. Serum leptin and plasma adiponectin concentration did not differ with either zinc supplementation or placebo. The levels of IL-6 and leptin were inversely associated with dietary zinc intake. These results suggest that zinc may have a favorable effect on obesity-related inflammation in young adults.     

Urinary tract candidiasis: report of a case with bilateral ureteral obstruction

A brief review of the literature on urinary tract candidiasis is presented. The presence of Candida albicans in the urine is rather uncommon and most patients have candiduria without any apparent disease. Among the others, three different clinical types of infection are recognized: (1) pyelonephritis, (2) lower urinary tract infection and (3) ureteral obstruction. Of this last type only seven cases were found in the literature; four of the patients died. We add one case in which the patient did very well after the obstruction of the ureters was relieved by means of ureteral catheters and a large urinary output was maintained for several days.     

A Real-Time PCR-Based Semi-Quantitative Breakpoint to Aid in Molecular Identification of Urinary Tract Infections

This study presents a novel approach to aid in diagnosis of urinary tract infections (UTIs). A real-time PCR assay was used to screen for culture-positive urinary specimens and to identify the causative uropathogen. Semi-quantitative breakpoints were used to screen for significant bacteriuria (presence of ≥10⁵ CFU/ml of uropathogens) or low-level bacteriuria (containing between 10³ and 10⁴ CFU/ml of uropathogens). The 16S rDNA-based assay could identify the most prevalent uropathogens using probes for Escherichia coli, Pseudomonas species, Pseudomonas aeruginosa, Staphylococcus species, Staphylococcus aureus, Enterococcus species and Streptococcus species. 330 urinary specimens were analysed and results were compared with conventional urine culture. Using a PCR Ct value of 25 as semi-quantitative breakpoint for significant bacteriuria resulted in a sensitivity and specificity of 97% and 80%, respectively. In 78% of the samples with monomicrobial infections the assay contained probes to detect the bacteria present in the urine specimens and 99% of these uropathogens was correctly identified. Concluding, this proof-of-concept approach demonstrates that the assay can distinguish bacteriuria from no bacteriuria as well as detect the involved uropathogen within 4 hours after sampling, allowing adequate therapy decisions within the same day as well as drastically reduce consequent urine culturing.     

Synthesis, characterization and electrochemistry of bis(3-aryl-6,6-dimethylcyclohexadienyl)ruthenium complexes

Five bis(3-aryl-6,6-dimethylcyclohexadienyl)ruthenium complexes (4a-4e) are prepared by reactions between di-μ-chlorodichlorobis[(1-3η:6-8η)-2,7-dimethyl-octadienyl]diruthenium and the corresponding dienes. The larger aryl substituents increase the barrier to rotation in 4a-4e relative to bis(3-methyl-6,6-cyclohexadienyl)ruthenium (5b). The activation parameters were determined by line-shape analysis for the exchange process in 4a: ΔG^† (183 K), 8.0 ± 0.2 kcal/mol; ΔH^†, 10.3 kcal/mol; and ΔS^†, 13 cal/mol/K. The electronic effect of the aryl substituents on the cyclohexadienyl ligand on the oxidation potential of the complex are compared to the effect of methyl substituents.     

Synthesis,anticancer activity,and SAR analyses of compounds containing the 5:7-fused 4,6,8-triaminoimidazo[4,5-e][1,3]diazepine ring system

Described herein are our limited structure–activity relationship (SAR) studies on a 5:7-fused heterocycle (1), containing the 4,6,8-triaminoimidazo[4,5-e][1,3]diazepine ring system, whose synthesis and potent broad-spectrum anticancer activity we reported a few years ago. Our SAR efforts in this study are mainly focused on judicial attachment of substituents at N-1 and N⁶-positions of the heterocyclic ring. Our results suggest that there is some subtle correlation between the substituents attached at the N-1 position and those attached at the N⁶-position of the heterocycle. It is likely that there is a common hydrophobic binding pocket on the target protein that is occupied by the substituents attached at the N-1 and N⁶-positions of the heterocyclic ligand. This pocket appears to be large enough to hold either a C-18 alkyl chain of N⁶ and no attachment at N-1, or a combined C-10 at N⁶ and a CH₂Ph at N-1. Any alkyl chain shorter or longer than C-10 at N⁶ with a CH₂Ph attached at N-1, would result in decrease of biological activity.     

Individual-specific muscle maximum force estimation using ultrasound for ankle joint torque prediction using an EMG-driven Hill-type model

EMG-driven models can be used to estimate muscle force in biomechanical systems. Collected and processed EMG readings are used as the input of a dynamic system, which is integrated numerically. This approach requires the definition of a reasonably large set of parameters. Some of these vary widely among subjects, and slight inaccuracies in such parameters can lead to large model output errors. One of these parameters is the maximum voluntary contraction force (F^om). This paper proposes an approach to find F^om by estimating muscle physiological cross-sectional area (PCSA) using ultrasound (US), which is multiplied by a realistic value of maximum muscle specific tension. Ultrasound is used to measure muscle thickness, which allows for the determination of muscle volume through regression equations. Soleus, gastrocnemius medialis and gastrocnemius lateralis PCSAs are estimated using published volume proportions among leg muscles, which also requires measurements of muscle fiber length and pennation angle by US. F^om obtained by this approach and from data widely cited in the literature was used to comparatively test a Hill-type EMG-driven model of the ankle joint. The model uses 3 EMGs (Soleus, gastrocnemius medialis and gastrocnemius lateralis) as inputs with joint torque as the output. The EMG signals were obtained in a series of experiments carried out with 8 adult male subjects, who performed an isometric contraction protocol consisting of 10 s step contractions at 20% and 60% of the maximum voluntary contraction level. Isometric torque was simultaneously collected using a dynamometer. A statistically significant reduction in the root mean square error was observed when US-obtained F^om was used, as compared to F^om from the literature.     

A comparison of acylation, phosphorylation and binding in related substrates and inhibitors of serum cholinesterase

1. The K_m and catalytic-centre activities for human serum cholinesterase and methyl, ethyl, n-propyl and n-butyl butyrate substrates were determined and compared with the related inhibition constants of a similarly substituted organophosphate inhibitor series based on malaoxon. The results indicated that the catalytic-centre activities approximated to k_+2(a), the acylation rate constant, and that K_m approximated to the equilibrium binding constant. The inhibition constants measured were K_a, the equilibrium binding constant, and k_+2(p), the phosphorylation rate constant. 2. The effects of the alkyl substituents on k_+2(p) and k_+2(a) were closely parallel, and the decreasing order in each case was: n-butyl; methyl; n-propyl; ethyl. The Taft constants did not follow this order, suggesting that alkyl substituents did not primarily effect acylation or phosphorylation by electron induction. 3. For comparable homologues, the k_+2(a) values were on average 435 times the k_+2(p) values. The k_+2(p) values at 25° and pH7·6 ranged from 6·6min.⁻¹ for the diethyl member to 22·6min.⁻¹ for the di-n-butyl member. 4. The effect of the alkyl substituents on K_a and K_m were closely paralleled. The increasing order in each case was: n-butyl; n-propyl; ethyl; methyl. The K_a values were about 100 times less than the comparable K_m values. 5. Consideration of the binding energies suggested that only one of the two alkyl groups on the malaoxon homologues bound to the active site. 6. The possibility that malaoxon acted as a substrate as well as an inhibitor for cholinesterase was also investigated, but no evidence of a substrate reaction was found.     

Arginase activity in frog urinary bladder epithelial cells and its involvement in regulation of nitric oxide production

The activity of arginase converting arginine into ornithine and urea is of particular interest among many factors regulating NO production in the cells. It is known that by competing with NO-synthase for common substrate (arginine), arginase can affect NO synthesis. In the present work, properties of arginase from the common frog Rana temporaria L. urinary bladder epithelial cells containing the NO-synthase were characterized, and possible contribution of arginase to regulation of NO production by epithelial cells was studied. It has been shown that the enzyme has temperature optimum in the range of 55–60°C, K _M for arginine 23 mM, and V _max about 10 nmole urea/mg of protein/min, and its activity was efficiently inhibited by (S)-(2-boronoethyl)-L-cysteine (BEC), an inhibitor of arginase, at concentrations from 10^?6 to 10^?4 M. The comparison of arginase activity in various frog tissues revealed the following pattern: liver > kidney > brain > urinary bladder (epithelium) > heart > testis. The arginase activity in isolated urinary bladder epithelial cells was 3 times higher that in the intact urinary bladder wall. To evaluate the role of arginase in regulation of NO production, the epithelial cells were cultivated in the media L-15 or 199 containing different amounts of arginine; the concentration of NO₂ ^?, the stable NO metabolites, was de-termined in the cultural fluid after 18–20 h of cell incubation. The vast majority of the produced nitrites are associated with NOS activity, as L-NAME, the NO inhibitor, decreased their accumulation by 77.1% in the L-15 medium and by 80% in the 199 medium. BEC (10^?4 M) increased nitrite production by 18.0% ± 2.7% in the L-15 medium and by 24.4% ± 3.5% in the 199 medium (p < 0.05). The obtained data indicate a relatively high activity of arginase in the frog urinary bladder epithelium and its involvement in regulation of NO production.     

C4 abundance in an Inner Mongolia grassland system is driven by temperature–moisture interaction,not grazing pressure

Global warming and CO₂ rise is expected to change the balance of C3 and C4 plants in grassland vegetation, but disturbance, including grazing, could also affect C3/C4 community structure. We used a six-year (2005–2010) grazing experiment to test the prediction that the relative abundance of C4 plants (P_C4) in the semi-arid grassland of Inner Mongolia is related to growing-period temperature and disturbance by grazing. Paddocks were stocked with sheep at six rates (0.375–2.25 sheep ha^?1 a^?1) between June and September. P_C4 was estimated from the relative ¹³C/¹²C composition (δ¹³C) of wool grown during the grazing period of each year and a two-member mixing model of the δ¹³C of the C3 and C4 communities in the paddocks. Stocking rate had a slight effect (<0.5‰) on the δ¹³C of the C3 and the C4 end-members. Annual average P_C4 varied between 5% and 24%. Stocking rate had no significant effect on P_C4 but the growing-season temperature had a large effect, and P_C4 increased with temperature. Importantly, the growing season shifted between years due to changing seasonal distribution of rainfall and soil moisture availability from winter precipitation causing large variation in temperature of the effective growing season. Changes in temperature and in amount and seasonal distribution of rainfall as a consequence of inter-annual fluctuations and long-term change can thus have a large impact on the C4 abundance and its spatial pattern.     

Resistant starch reduces large intestinal pH and promotes fecal lactobacilli and bifidobacteria in pigs

Dietary resistant starch (RS) may have prebiotic properties but its effects on fermentation and the microbial population are inconsistent. This meta-analysis aimed to quantify the relationship between RS type 2 (RS2) and intestinal short-chain fatty acids (SCFA) and pH as well as certain key bacterial taxa for intestinal health in pigs. From the 24 included articles with sufficient information about the animal, and dietary and physiological measurements published between 2000 and 2017, individual sub-data sets for fermentation metabolites, pH, bacterial abundances and apparent total tract digestibility were built and used to parameterize prediction models on the effect of RS2, accounting for inter- and intra-study variability. In addition, the effect of pig’s BW at the start of the experiment and duration of the experimental period on response variables were also evaluated using backward elimination analysis. Dietary RS levels ranged from 0% to 78.0% RS, with median and mean RS levels of 28.8% and 23.0%, respectively. Negative relationships could be established between dietary RS and pH in the large intestine (P<0.05), with a stronger effect in the mid and distal colon, and feces (R²=0.64 to 0.81; P<0.001). A dietary level of 15% RS would lower the pH in the proximal, mid-, distal colon and feces by 0.2, 0.6, 0.4 and 0.6 units, respectively. Increasing RS levels, however, did not affect SCFA concentrations in the hindgut, but enhanced the molar proportion of propionate in mid-colon and reduced those of acetate in mid-colon and of butyrate in mid- and distal colon (R²=0.46 to 0.52; P<0.05). Backward elimination indicated an age-related decrease in mid-colonic propionate proportion and increase in mid- and distal colonic butyrate proportion (P<0.05), thereby modulating RS2 effects. In feces, increasing RS levels promoted fecal lactobacilli (R²=0.46; P<0.01) and bifidobacteria (R²=0.57; P<0.01), whereby the slope showed the need for a minimal RS level of 10% for a 0.5 log unit-increase in their abundance. Best-fit equations further supported that a longer experimental period increased fecal lactobacilli but decreased fecal bifidobacteria (P<0.05). In conclusion, dietary RS2 seems to effectively decrease digesta pH throughout the large intestine and increase lactic acid-producing bacteria in feces of pigs which may limit the growth of opportunistic pathogens in the hindgut. To achieve these physiologically relevant changes, dietary RS should surpass 10% to 15%.     

Regulation of urinary thromboxane B2 in man: Influence of urinary flow rate and tubular transport

Thromboxane B₂ (TxB) is excreted in human urine, but the mechanism of renal excretion and the quantitative relationship of urinary TxB to the active parent compound, thromboxane A₂, of renal or extrarenal origin is not established. To determine the effects of vasoactive hormones, uricosuric agents and urinary flow rate on TxB excretion, urinary TxB was measured by radioimmunoassay and mass spectrometry, and renal metabolism of blood TxB was determined by radiochromatography of urine after i.v. [³H]-TxB infusions. Basal TxB was 6.7 ± 1.1 ng/h during an oral water load, and TxB fell with s.q. antidiuretic hormone (to 3.4 ± 0.4 ng/h, P<0.01) and with fluid restriction (to 2.6 ± 0.5 ng/hr, P=0.001) in parallel with urinary volume. Urinary excretion of unmetabolized [³H]-TxB also fell (by 56%) with fluid restriction, implicating altered metabolism rather than synthesis as the mechanism of the urinary flow effect. Angiotensin II infusions slightly reduced both TxB and urine volume, consistent with a flow effect. In contrast, probenecid did not alter urine volume, but increased urinary uric acid (by 244%), TxB (from 5.6 ± 0.9 to 11.1 ± 2.9 ng/h) and urinary excretion of blood [³H]-TxB (by 243%) by similar amounts (all P<0.05), suggesting that TxB is actively reabsorbed in the proximal tubule, similarly to uric acid. Thus, urinary excretion of TxB of renal and extrarenal origin is regulated by proximal and distal tubule factors.     

Quantitative aspect of the myofibrillar protein turnover in transient state on dietary protein depletion and repletion revealed by urinary excretion of Nτ-Methylhistidine

The fractional rates of synthesis and breakdown of myosin and actin in skeletal muscle of younn adult male rats were measured during 2 weeks of ad libitum feeding of a protein-free diet, and 8 days of refeeding with an adequate protein diet. Daily urinary excretion of N^τ-Methylhistidine (3-methylhistidine) by the N^τ-methylhistidine pool of the body gave the fractional breakdown rate of the myosin-actin pool. The fractional synthesis rate of the myosin-actin pool was calculated from the fractional breakdown rate and the size of N^τ-methylhistidine pool in the body. The feeding of the protein-free diet resulted in a decreased in body weight and a decrease in daily urinary excretion of N^τ-methylhistidine. Refeeding caused an increase in body weight and a progressive increase in daily urinary excretion of N^τ-methylhistidine. At the start of the experiment, the fractional breakdown rate of the myosin-actin pool was 4% per day and with prolonged protein depletion, the rate decreased to 1.25% per day. The fractional synthesis rate also decreased more rapidly than the breakdown rate. On refeeding for one day with an adequate protein diet, the fractional synthesis rate increased from 0.75 to 5.75% per day. Accumulation of skeletal muscle protein by refeeding was accompanied by a difference between the faster rate of synthesis and slower rate of breakdown even though the fractional breakdown rate increased during the rehabilitation period.