Purification and properties of glutamine synthetase from the non-N2-fixing cyanobacterium Phormidium laminosum.

Soluble glutamine synthetase activity (L-glutamate:ammonia ligase, ADP forming, EC 6.3.1.2) was purified to electrophoretic homogeneity from the filamentous non-N2-fixing cyanobacterium Phormidium laminosum (OH-1-p.Cl1) by using conventional purification procedures in the absence of stabilizing ligands. The pure enzyme showed a specific activity of 152 mumol of gamma-glutamylhydroxamate formed.min-1 (transferase activity), which corresponded to 4.4 mumol of Pi released.min-1 (biosynthetic activity). The relative molecular mass of the native enzyme was 602 kilodaltons and was composed of 12 identically sized subunits of 52 kilodaltons. Biosynthetic activity required the presence of Mg2+ as an essential activator, although Co2+ and Zn2+ were partially effective. The kinetics of activation by Mg2+, Co2+, and Zn2+ were sigmoidal, and concentrations required for half-maximal activity were 18 mM (h = 2.2), 6.3 mM (h = 5.6), and 6.3 mM (h = 2.45), respectively. However, transferase activity required Mn2+ (Ka = 3.5 microM), Cu2+, Co2+, or Mg2+ being less effective. The substrate affinities calculated for L-Glu, ammonium, ATP, L-Gln, and hydroxylamine were 15, 0.4, 1.9 (h = 0.75), 14, and 4.1 mM, respectively. Optimal pH and temperature were 7.2 and 55 degrees C for biosynthetic activity and 7.5 and 45 degrees C for transferase activity. The biosynthetic reaction mechanism proceeded according to an ordered three-reactant system, the binding order being ammonium, L-Glu, and ATP. The presence of Mn2+ or Mg2+ drastically affected the thermostability of transferase and biosynthetic activities. Heat inactivation of biosynthetic activity in the presence of Mn2+ obeyed first-order kinetics, with an Ea of 76.8 kcal (ca. 321 kJ) mol-1. Gly, L-Asp, L-Ala, L-Ser and, with lower efficiency, L-Lys and L-Met, L-Lys, and L-Glu inhibited only transferase activity. No cumulative inhibition was observed when mixtures of amino acids were used. Biosynthetic activity was inhibited by AMP (Ki= 7 mM), ADP (Ki= 2.3 mM), p-hydroxymercuribenzoate (Ki= 25 microM), and L-methionine-D, L-sulfoximine (Ki= 2 microM). The enzyme was not activated in vitro by chemically reduced Anabaena thioredoxin. This is the first report of glutamine synthetase activity purified from a filamentous non-N2-fixing cyanobacterium.     

Aromatase activity, serum oestradiol and their correlation with demographic indices

Peripheral aromatase activity was measured in 24 postmenopausal women suffering from advanced breast cancer. The % conversion of androstenedione to oestrone was then assessed for a significant correlation with age, weight, height, Quetelets index (weight/height², Q.I.) and length of menopause. Serum oestradiol (E₂) levels were measured in 22 of the subjects and compared with the same indices. There was no correlation between E₂ or aromatase activity with the length of menopause (P = 0.3 and P = 0.5, respectively). In our data aromatase activity did not correlate with age (P > 0.5, N = 22). Serum E₂ levels (P = 0.07, N = 20) expressed a negative correlation (i.e. decreased) with age. There was also a poor correlation between aromatase activity and weight of Quetelets index (P = 0.3, N = 20 for both). Serum E₂ levels showed a statistically significant correlation with weight (P = 0.01, N = 21), but the relationship with Quetelets index just failed to attain statistical significance (P = 0.07, N = 20). In both cases the regression line was positive. When aromatase activity was correlated with serum E₂ levels the regression line was positive but not statistically significant (P = 0.4, N = 22). The data indicate that aromatase activity is only one factor determining the differences in serum E₂ levels between postmenopausal women.     

Correlates of objectively measured physical activity in obese children

The aim of this study was to identify potential correlates of objectively measured physical activity in a sample of obese children. A cross-sectional design was used to assess 137 5-9-year-old obese children (mean +/- s.d. age = 8.3 +/- 1.1 years; mean BMI z-score = 2.76 +/- 0.70; 58% girls) from two regional cities in New South Wales, Australia, before commencement in a treatment trial. Correlates examined included age, BMI z, parental BMI, perceived competence, health-related quality of life, daily minutes spent in small screen recreation (SSR), and fundamental motor skill (FMS) proficiency. Physical activity was assessed using accelerometers and values were calculated for % of monitored time spent in moderate- (MPA) and vigorous (VPA)-intensity physical activity and mean counts per minute (CPM). Analyses were conducted separately for boys and girls. Motor skill proficiency was significantly correlated with a number of physical activity variables for boys and girls. For boys, regression analysis revealed object-control proficiency predicted CPM (R(2) = 0.25) and age was a predictor of %MPA (R(2) = 0.56). Age and object-control skill proficiency were salient predictors of %VPA (R(2) = 0.34). For girls, age and daily minutes of SSR were the only significant predictors for CPM (R(2) = 0.13). Age was the sole predictor of %MPA (R(2) = 0.38) and %VPA (R(2) = 0.15). The targeting of FMSs at an early age should be tested in experimental studies as potential strategies to increase physical activity among obese children, particularly for boys. Interventions aimed at reducing sedentary behaviors among obese girls should also be considered.     

Surface electromyographic assessment of the effect of dynamic activity and dynamic activity with static stretching of the gastrocnemius on vertical jump performance

The purpose of this study was to investigate the effects of dynamic activity and dynamic activity/static stretching of the gastrocnemius muscle on vertical jump (VJ) performance. Additionally, muscle activity was recorded using electromyography. Thirteen healthy adults (7 men and 6 women) with a mean age of 26 +/- 4 years served as subjects. The average jump height and muscle activity from 3 separate maximal VJ attempts were performed at the start of each session to be used as baseline measures using the Kistler force plate and the Noraxon telemetry EMG unit. Subjects then performed 1 of 2 protocols: dynamic activity only or dynamic activity with static stretching. Each protocol was followed by 3 maximal VJ trials. Average VJ height was analyzed using a 2 (time: pre, post) x 2 (prejump protocol: dynamic activity, dynamic activity + stretching) analysis of variance with repeated measures on both factors. A paired-samples t-test was used to compare the intraday difference scores for EMG activity between the 2 conditions. Jump height was not influenced by the interaction of pre-post and protocol (p = 0.0146. There was no difference for the main effects of time (p = 0.274) and pre-jump protocol (p = 0.595). Gastrocnemius muscle activity was likewise not different for the 2 prejump protocols (p = 0.413). The results from this study imply that the use of static stretching in combination with dynamic activity of the gastrocnemius muscle does not appear to have an adverse affect on VJ height performance. The practical importance concerns the warm-up routine that coaches and athletes employ; that is, they may want to consider including an aerobic component when statically stretching the gastrocnemius immediately prior to a vertical jumping event.     

PLTP activity in premenopausal women. Relationship with lipoprotein lipase, HDL, LDL, body fat, and insulin resistance

Plasma phospholipid transfer protein (PLTP) is thought to play a major role in the facilitated transfer of phospholipids between lipoproteins and in the modulation of high density lipoprotein (HDL) particle size and composition. However, little has been reported concerning the relationships of PLTP with plasma lipoprotein parameters, lipolytic enzymes, body fat distribution, insulin, and glucose in normolipidemic individuals, particularly females. In the present study, 50 normolipidemic healthy premenopausal females were investigated. The relationships between the plasma PLTP activity and selected variables were assessed. PLTP activity was significantly and positively correlated with low density lipoprotein (LDL) cholesterol (r(s) = 0.53), apoB (r(s) = 0.44), glucose (r(s) = 0.40), HDL cholesterol (r(s) = 0.38), HDL(3) cholesterol (r(s) = 0.37), lipoprotein lipase activity (r(s) = 0.36), insulin (r(s) = 0.33), subcutaneous abdominal fat (r(s) = 0.36), intra-abdominal fat (r(s) = 0.29), and body mass index (r(s) = 0.29). HDL(2) cholesterol, triglyceride, and hepatic lipase were not significantly related to PLTP activity. As HDL(2) can be decreased by hepatic lipase and hepatic lipase is increased in obesity with increasing intra-abdominal fat, the participants were divided into sub-groups of non-obese (n = 35) and obese (n = 15) individuals and the correlation of PLTP with HDL(2) cholesterol was re-examined. In the non-obese subjects, HDL(2) cholesterol was found to be significantly and positively related to PLTP activity (r(s) = 0.44). Adjustment of the HDL(2) values for the effect of hepatic lipase activity resulted in a significant positive correlation between PLTP and HDL(2) (r(s) = 0.41), indicating that the strength of the relationship between PLTP activity and HDL(2) can be reduced by the opposing effect of hepatic lipase on HDL(2) concentrations. We conclude that PLTP-facilitated lipid transfer activity is related to HDL and LDL metabolism, as well as lipoprotein lipase activity, adiposity, and insulin resistance.     

Toxicological effects of methylmercury on walleye (Sander vitreus) and perch (Perca flavescens) from lakes of the boreal forest

Biochemical and physiological responses of walleye (Sander vitreus) and perch (Perca flavescens) were studied in four Canadian boreal forest lakes representing a mercury (Hg) exposure gradient. The aim of this study was to assess the effects of Hg and methylmercury (MeHg) on the general physiological condition of fish as well as to gauge the relationship between MeHg and the glutathione (GSH) system in metal-contaminated and reference sites using a series of biomarkers. Walleye from Lake Malartic had the highest liver MeHg concentrations, exhibited lower hepatosomatic indices (HSI) and lower glutathione S-transferase (GST) activity. HSI was negatively related to liver total Hg concentrations in walleye (R2=0.33, n=108, P<0.0001). Glutathione reductase (GR) and GST activity for walleye from Lake Malartic were related to HSI (R2=0.38, n=25, P=0.0010; R2=0.46, n=27, P<0.0001, respectively). In Lake Desjardins-East, where perch had the highest liver MeHg concentrations, glutathione peroxidase selenium dependent activity (GSH-Px SD) and GST activity were negatively related to liver MeHg concentrations (R2=0.39, n=21, P=0.0026; R2=0.22, n=21, P=0.0298, respectively). This study suggests that Hg may induce adverse effects on the physiology and cellular metabolism of walleye and perch at environmentally relevant concentrations.     

大兴安岭地区紫貂的活动节律

借助无线电遥测技术,对４只紫貂全年的活动节律进行了研究,结果表明,紫貂的活动节律春季和冬季的高峰是在晨昏二个阶段,夏秋二季的活动高峰在白昼。春季总体活动节律与夏季相比有明显差异（Ｆ＝４．４９９,ｄｆ＝１,２２,２３;Ｐ＝０．０４５）,春季与秋季的活动节律也有差异（Ｆ＝７．０３９;ｄｆ＝１,２２,２３;Ｐ＝０．０１５）。其总体平均活动强度,春季活动量最小（１７．５３％）,夏季最高（３８．２９％）,其     

Inhibition of trout (Salmo gairdneri R.) PBG-synthase by some metal ions (Mg2+, Pb2+, Zn2+)

The effect of metal ions on the activity of trout kidney and liver PBG-synthase was investigated. Heavy metals inhibited the kidney enzyme in a complex manner. Kinetic analysis of the inhibition of liver activity by Pb2+ (Ki = 1.3 mM) was consistent with non-competitive inhibition, whereas Zn2+ (Ki = 1.3 mM) and Mg2+ (Ki = 3.5 mM) were competitive inhibitors.     

Determinants of low HDL levels in familial combined hyperlipidemia

In familial combined hyperlipidemia (FCHL), affected family members frequently have reduced levels of HDL cholesterol, in addition to elevated levels of total cholesterol and/or triglycerides (TGs). In the present study, we focused on those determinants that are important regulators of HDL cholesterol levels in FCHL, and measured postheparin plasma activities of hepatic lipase (HL), lipoprotein lipase, cholesterol ester transfer protein, and phospholipid transfer protein (PLTP) in 228 subjects from 49 FCHL families. In affected family members (n = 88), the levels of HDL cholesterol, HDL2 cholesterol, HDL3 cholesterol, and apolipoprotein A-I were lower than in unaffected family members (n = 88) or spouses (n = 52). The main change was the reduction of HDL2 cholesterol by 25.4% in affected family members (P < 0.001 vs. unaffected family members; P = 0.003 vs. spouses). Affected family members had higher HL activity than unaffected family members (P = 0.001) or spouses (P = 0.013). PLTP activity was higher in affected than unaffected family members (P = 0.025). In univariate correlation analysis, a strong negative correlation was observed between HL activity and HDL2 cholesterol (r = -0.339, P < 0.001). Multivariate regression analysis demonstrated that gender, HL activity, TG, and body mass index have independent contributions to HDL2 cholesterol levels. We suggest that in FCHL, TG enrichment of HDL particles and enhanced HL activity lead to the reduction of HDL cholesterol and HDL2 cholesterol.     

Onset of secretion of proteins with antiviral activity by pig conceptuses

In Exp. 1, antiviral activity was detected in Day-15 pregnant uterine flushings (6222 +/- 2167 units/ml) and in conceptus culture medium collected at 0, 1, 2, 4, 8, 16, 24, 32, 40, and 48 h (95, 375, 650, 1216, 1600, 2100, 2017, 2083, 3500 and 5000 units/ml, respectively; R2 = 0.81, P less than 0.01; y = 190.0 + 252.7x - 11.2x2 + 0.2x3. In Exp. 2, antiviral activity of Day-15 conceptus culture medium was reduced 99% after boiling for 20 min (P less than 0.01) and, after 18 h dialysis (6000-8000 Mr cut-off), 100% of the activity was in the retentate. In Exp. 3, antiviral activity was not detected in cultures of conceptuses from Days 10 and 11 and activity was maximal for Day 14 and Day 15 conceptuses (2100 and 2083 units/ml, respectively). Effects of day were best described by a quadratic regression equation (y = 17,652 - 3263x + 150x2; R2 = 0.55, P less than 0.01). In Exp. 4, changes in antiviral activity detected in uterine flushings from pregnant gilts on Days 8, 10, 11, 12, 14 and 15 (1.3, 0, 6.7, 63.3, 580 and 1663 units/ml, respectively) were described by the equation y = -20,743 + 6189x - 606x2 + 20x3 (R2 = 0.85, P less than 0.01). In Exp. 5, low antiviral activities (5-30 units/ml) were detected in all plasma samples collected from the uterine artery and uterine vein of pregnant and cyclic gilts, but values were not significantly influenced by pregnancy status, day or site of collection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Optimization of antibacterial activity by Gold-Thread (Coptidis Rhizoma Franch) against Streptococcus mutans using evolutionary operation-factorial design technique

This study was conducted to find the optimum extraction condition of Gold-Thread for antibacterial activity against Streptococcus mutans using The evolutionary operation-factorial design technique. Higher antibacterial activity was achieved in a higher extraction temperature (R2 = -0.79) and in a longer extraction time (R2 = -0.71). Antibacterial activity was not affected by differentiation of the ethanol concentration in the extraction solvent (R2 = -0.12). The maximum antibacterial activity of clove against S. mutans determined by the EVOP-factorial technique was obtained at 80 degrees C extraction temperature, 26 h extraction time, and 50% ethanol concentration. The population of S. mutans decreased from 6.110 logCFU/ml in the initial set to 4.125 logCFU/ml in the third set.     

Antimicrobial and cytotoxicity activities of the medicinal plant Primula macrophylla

Primula macrophylla (Primulaceae) is reported as to be useful in asthma, restlessness, insomnia and fish poisoning. Antifungal and toxic activities of crude extract, fractions and a pure isolated compound exhibited statistically significant activities. Excellent antifungal activity was found in the crude extract, benzene and ethyl acetate fractions against T. longifusis and against M. canis with different MIC values. Antileishmanial activity (IC(50) = 50ug/mL) was observed as compared to standard drug Amphotericin B, and cytotoxic activity (LD(50) = 47.919microg/mL) was also found in the chloroform fraction. While pure compound 2-phenylchromone (Flavone) isolated from the chloroform fraction showed good activity (IC(50) = 25microg/mL) against Leishmania and cytotoxicity (LD(50) = 2.0116 microg/mL) in Brine Shrimp experiments. From antileishmanial and cytotoxic activity it can be concluded that 2-phenylchromone is the major compound responsible for these activities.     

A sensitive capillary GC assay for the determination of sparteine oxidation products in microsomal fractions of human liver

A sensitive method for the assay of sparteine oxidase activity in vitro by microsomal fractions of human liver is described. The activity of sparteine oxidase was assessed by the formation of 2- and 5-dehydrosparteines, which were estimated by capillary gas chromatography with N2-FID detection. The limit of detection of the two metabolites, 2- and 5-dehydrosparteine, was 10 pmol (2.3 ng) per sample. Sparteine oxidase activity was linear with microsomal protein concentration ranging from 25 to 200 ug and with incubation times between 5 and 60 minutes. Omission of NADPH on incubation under an atmosphere of carbon monoxide inhibited formation of both metabolites, thus indicating that aforementioned metabolites arise in reaction catalyzed by cytochrome P-450. In three liver samples from humans classified as extensive (EM) metabolizers the formation of 2- and 5-dehydrosparteines was observed, 2-dehydrosparteine being the major metabolite. In these samples sparteine oxidase activity was characterised by Vmax = 136 +/- 53 pmol/min/mg and Km = 44 +/- 12 microM for 2-dehydrosparteine formation. For 5-dehydrosparteine formation the following values were obtained: Vmax = 57 +/- 18 pmol/min/mg and Km = 42 +/- 26 microM. In a liver sample from a poor metabolizer (PM) only the formation of 2-dehydrosparteine was detected with the method of analysis used. In this sample a great increase in Km (Km PM = 3033 microM) was noted, while Vmax was very similar to those obtained for 2-dehydrosparteine formation in EM subjects (Vmax PM = 147 pmol min/mg).     

Characterization of patatin esterase activity in AOT-isooctane reverse micelles

Patatin is a family of glycoproteins that accounts for 30-40% of the total soluble protein in potato (Solanum tuberosum L.) tubers. This protein has been reported not only to serve as a storage protein but also to exhibit lipid acyl hydrolase (LAH) activity. In this study patatin is characterized in AOT-isooctane reverse micelles. The influence on the enzymatic activity of characteristic parameters of reverse micelles, w(o) (= H(2)O/AOT), and the percentage of H(2)O, theta, were investigated. The results obtained show that patatin esterase activity varies with w(o) but remains constant throughout the range of theta values studied. The variation with w(o) showed that the activity follows an S-shaped behavior pattern, reaching a maximum at about w(o) = 20 for 2% H(2)O. Patatin esterase activity was compared with p-nitrophenyl (PNP) fatty acid esters of different chain lengths. The activity was much higher for PNP-caprylate. The pH optimum was 6.0, different from the value obtained when patatin esterase activity was measured in mixed micelle systems. The optimal temperature was 35 degrees C, above which the activity decreased to almost zero. The kinetic parameters were also evaluated (K(m) = 10 mM, V(m) = 158 microM/min, V(m)/K(m) = 15.8 x 10(-3) min(-1)). This paper shows the suitability of reverse micelles for measuring patatin esterase activity, since it allows the study of the enzyme in similar conditions to that prevailing in vivo.     

Phosphatase activity in rat adipocytes: effects of insulin and insulin resistance

Insulin regulates the activity of both protein kinases and phosphatases. Little is known concerning the subcellular effects of insulin on phosphatase activity and how it is affected by insulin resistance. The purpose of this study was to determine insulin-stimulated subcellular changes in phosphatase activity and how they are affected by insulin resistance. We used an in vitro fatty acid (palmitate) induced insulin resistance model, differential centrifugation to fractionate rat adipocytes, and a malachite green phosphatase assay using peptide substrates to measure enzyme activity. Overall, insulin alone had no effect on adipocyte tyrosine phosphatase activity; however, subcellularly, insulin increased plasma membrane adipocyte tyrosine phosphatase activity 78 +/- 26% (n = 4, P < 0.007), and decreased high-density microsome adipocyte tyrosine phosphatase activity 42 +/- 13% (n = 4, P < 0.005). Although insulin resistance induced specific changes in basal tyrosine phosphatase activity, insulin-stimulated changes were not significantly altered by insulin resistance. Insulin-stimulated overall serine/threonine phosphatase activity by 16 +/- 5% (n = 4, P < 0.005), which was blocked in insulin resistance. Subcellularly, insulin increased plasma membrane and crude nuclear fraction serine/threonine phosphatase activities by 59 +/- 19% (n = 4, P < 0. 005) and 21 +/- 7% (n = 4, P < 0.007), respectively. This increase in plasma membrane fractions was inhibited 23 +/- 7% (n = 4, P < 0. 05) by palmitate. Furthermore, insulin increased cytosolic protein phosphatase-1 (PP-1) activity 160 +/- 50% (n = 3, P < 0.015), and palmitate did not significantly reduce this activity. However, palmitate did reduce insulin-treated low-density microsome protein phosphatase-1 activity by 28 +/- 6% (n = 3, P < 0.04). Insulin completely inhibited protein phosphatase-2A activity in the cytosol and increased crude nuclear fraction protein phosphatase-2A activity 70 +/- 29% (n = 3, P < 0.038). Thus, the major effects of insulin on phosphatase activity in adipocytes are to increase plasma membrane tyrosine and serine/threonine phosphatase, crude nuclear fraction protein phosphatase-2A, and cytosolic protein phosphatase-1 activities, while inhibiting cytosolic protein phosphatase-2A. Insulin resistance was characterized by reduced insulin-stimulated serine/threonine phosphatase activity in the plasma membrane and low-density microsomes. Specific changes in phosphatase activity may be related to the development of insulin resistance.     

Relative luteinizing hormone-stimulable adenylyl cyclase of the preovulatory follicle: a predictor of ovulation in the domestic hen

The regulation of the ovulatory cycle of the hen (Gallus domesticus) is an enigma. The hen's ovulatory cycle is approximately 26 h in length. She lays an egg each day at a progressively later time. The hen then skips a day, resets her "clock", and a new sequence is started. We investigated if the ovary regulates the ovulatory cycle. Our biologic endpoint was the measurement of basal and luteinizing hormone (LH)-stimulable adenylyl cyclase (AC) activity in granulosa layers of the largest (F1) and second largest (F2) follicles. F1 and F2 follicles were obtained at lights off on nights before the first (C1; n = 7), second (C2; n = 7), or terminal ovulation (CT; n = 5) or the night before the day when no ovulation was expected (Cskip; n = 6). F1 and F2 follicles removed on C1, C2, CT, and Cskip had been these specific follicles for 32 h, 12 h, 10 h, and 8 h, respectively. Mean basal activity (pmol/min/mg protein) for the follicles was: C1 = 27.2, C2 = 44.1, CT = 60.5, and Cskip = 68.7. No significant differences were found in LH-stimulable AC activities of these F1 follicles. Relative LH (expressed as fold increase over basal) stimulation was significantly correlated (P less than 0.001) with maturity of the F1 follicle (C1 greater than C2 greater than CT greater than Cskip). No differences in AC activity were found for the F2 follicles whether they were C1, C2, CT or Cskip. For the Cskip, relative LH AC activity for the F1 follicle (2.8) was similar to that for the F2 follicle (2.7).(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamics of activities of matrix metalloproteinases-9 and -2, and the tissue inhibitors of MMPs in fetal fluid compartments during gestation and at parturition in the mare

During late gestation in the mare, rapid fetal growth is accompanied by considerable placental growth and further invasion of the endometrium by microvilli. This growth requires extensive remodeling of the extracellular matrix (ECM). In early pregnancy, we know that matrix metalloproteinase (MMP)-9 and -2 are involved in the endometrial invasion during endometrial cup formation. The present study investigated whether MMPs are found in fetal fluids later in gestation and during parturition, and if there was a difference in their activities between normal and preterm delivery. Amniotic fluids were collected from pony mares during the latter half of gestation, and amniotic and allantoic fluids from pony and thoroughbred mares at foaling. The fluids were analysed for the activity of MMP-9 and -2, and TIMPs using zymography techniques. There was an increase (P = 0.002) in activity of latent MMP-9 when approaching normal foaling, and a decrease (P < 0.001) during foaling. MMP-2 activity did not change through gestation, or during foaling. When comparing samples from pregnancies resulting in preterm deliveries with samples from foaling mares, the activity of MMP-9 was lower (P < 0.001) and MMP-2 activity was higher (P = 0.004) during foaling than preceding preterm delivery. The activity of MMP-9 was lower (P = 0.002) prior to preterm delivery than before delivery of a live foal at term, whereas no difference (P = 0.07) was demonstrated for latent MMP-2 activity when comparing the same groups. The activity of TIMP-2 was higher (P < 0.001) in the pre-parturient period before normal foaling than preceding preterm delivery. These results suggest that MMPs may have a role as markers for high risk pregnancy in the mare.     

Effects of Mn2+ on the exchange reaction of phosphoenolpyruvate carboxykinase in the presence of high concentrations of Mg2+

The mitochondrial phosphoenolpyruvate carboxykinase (GTP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32), purified from chick embryo liver, was synergistically activated by a combination of Mn2+ and Mg2+ in the oxaloacetate ---- H14CO-3 exchange reaction. Increases in the Mg2+ concentration caused decreases in the K0.5 value of Mn2+ in line with the earlier finding that the enzyme was markedly activated by low Mn2+ (microM) plus high Mg2+ (mM). In the presence of 2.5 mM Mg2+, increases in the Mn2+ level first enhanced the activity of phosphoenolpyruvate carboxykinase, and then suppressed it to the maximal velocity shown in the presence of Mn2+ alone. Kinetic studies showed that high Mn2+ inhibited the activity of Mg2+ noncompetitively, and those of GTP and oxaloacetate uncompetitively. The inhibition constant for oxaloacetate (K'i = 550 microM) was lower than that of Mg2+ (Ki = K'i = 860 microM) or GTP (K'i = 1.6 mM), and was nearly equal to the apparent half-maximal inhibition concentration of Mn2+. These results suggested that Mn2+ can play two roles, of activating and suppressing phosphoenolpyruvate carboxykinase activity in the presence of high Mg2+.