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Metabolism of steroid acetates by Streptomyces albus 总被引:1,自引:0,他引:1
Fermentation of 16-dehydropregnenolone acetate (1a) with Streptomyces albus yielded 16-dehydropregnenolone (1b) and 16-dehydroprogesterone (IIa). Similar incubation of pregnenolone acetate (Ic) with the strain afforded pregnenolone (Id), progesterone (IIb) and 20 alpha-hydroxy progesterone (IIc) while dehydroepiandrosterone acetate (IIIa) under the conditions was converted to dehydroepiandrosterone (IIIb), androstenedione (IVa) and testosterone (IVc). The strain was also capable of converting testosterone acetate (IVb) having the 17-acetoxy function in the 5-membered D-ring to testosterone (IVc) and androstenedione (IVa). All the products were identified by the application of various chemical and spectrometric techniques. 相似文献
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Phosphorus Stress-Induced Proteoid Roots Show Altered Metabolism in Lupinus albus 总被引:12,自引:2,他引:10
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Proteoid roots develop in Lupinus albus L. in response to nutrient stress, especially P. Proteoid roots excrete citrate and thus increase the availability of P, Fe, and Mn in the rhizosphere. In an effort to understand citrate synthesis and organic acid metabolism in proteoid roots of lupin, we have evaluated in vitro enzyme activities of citrate synthase (CS), malate dehydrogenase (MDH), and phosphoenolpyruvate carboxylase (PEPC) in proteoid and normal roots of plants grown with or without P. Organic acid concentrations, respiration rates, and dark 14CO2-labeling patterns were also determined. The in vitro specific activities of CS, MDH, and PEPC and in vivo dark 14CO2 fixation were higher in proteoid roots compared to normal roots, particularly under P stress. Western blot analysis showed that PEPC enzyme protein was more highly expressed in -P proteoid roots compared to other tissues. The majority of the fixed 14C was found in organic acids, predominantly malate and citrate. A larger fraction of citrate was labeled in P- stressed proteoid roots compared to other root tissue. Respiration rates of proteoid roots were 31% less than those of normal roots. The data provide evidence for increased synthesis of citrate in proteoid roots compared to normal roots, particularly under P stress. A portion of the carbon for citrate synthesis is derived from nonautotrophic CO2 fixation via PEPC in proteoid roots. 相似文献
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Sucrose Metabolism in Lupinus albus L. Under Salt Stress 总被引:3,自引:0,他引:3
Salt stress (50 and 150 mM NaCl) effects on sucrose metabolism was determined in Lupinus albus L. Sucrose synthase (SS) activity increased under salt stress and sucrose phosphate synthase activity decreased. Acid invertase
activity was higher at 50 mM NaCl and decreased to control levels at 150 mM NaCl. Alkaline invertase activity increased with
the salt stress. Glucose content decreased with salt stress, sucrose content was almost three times higher in plants treated
with 150 mM NaCl and fructose content did not change significantly. The most significant response of lupin plants to NaCl
excess is the increase of sucrose content in leaves, which is partially due to SS activity increase under salinity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Significant activities of the four enzymes needed to convert arginine into proline and glutamate (arginase, ornithine aminotransferase, pyrroline-5-carboxylate reductase and pyrroline-5-carboxylate dehydrogenase) develop co-ordinately in lactating rat mammary glands in proportion to the increased production of milk. No enzymes were detected to carry out the reactions of proline oxidation or reduction of glutamate to pyrroline-5-carboxylate. Minces of the gland converted ornithine into proline and into glutamate plus glutamine. These conversions increased during the cycle of lactation in proportion to the increased milk production and to the content of the necessary enzymes. The minced gland did not convert labelled ornithine into citrulline, confirming the absence from the gland of a functioning urea cycle, and did not convert labelled proline or glutamate into ornithine. A metabolic flow of labelled arginine to proline and glutamate in mammary gland was confirmed in intact animals with experiments during which the specific radioactivity of proline in plasma remained below that of the proline being formed from labelled arginine within the gland. It was concluded that arginase in this tissue had a metabolic role in the biosynthesis of extra proline and glutamate needed for synthesis of milk proteins. 相似文献
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Ruminococcus albus is an important fibrolytic bacterium in the rumen. Cellobiose is metabolized by this organism via hydrolytic and well as
phosphorylytic enzymes, but the relative contributions of each pathway were not clear. The cellobiose consumption rate by
exponentially growing cells was less than that of crude extracts (75 versus 243 nmol/min/mg protein). Cellobiose phosphorolytic
cleavage was much greater than hydrolytic activity (179 versus 19 nmol/min/mg protein) indicating that phosphorylases were
key enzymes in the initial metabolism of the soluble products of cellulose degradation. Cellodextrin phosphorylase appeared
to be active against substrates as large as cellohexaose. Phosphorylase activities were cytoplasmic, but hydrolytic activities
were associated with both the membrane and cytoplasmic fractions. Free glucose was phosphorylated with a GTP-dependent glucokinase,
and this enzyme showed 20-fold higher activity with GTP or ITP (>324 nmol/min/mg protein) than with ATP, UTP, CTP, GDP, or
PEP. The activity was decreased at least 57% when mannose, 2-deoxyglucose, or fructose was used as substrate compared with
glucose. The K
m
s for glucose and GTP were 321 and 247 μM, respectively. Since phosphorolytic cleavage conserves more metabolic energy than
simple hydrolysis, it is likely that such pathways provide for more efficient growth of R. albus in substrate-limiting conditions like those found in the rumen.
Received: 24 February 1997 / Accepted: 31 March 1997 相似文献
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Miao DC Velaphi SC Roy T Despain K Rosenfeld CR 《American journal of physiology. Endocrinology and metabolism》2008,295(3):E672-E677
Arginine vasopressin (AVP) is an important regulator of cardiovascular homeostasis in the fetus, but its role after birth is unclear. Although infused AVP increases mean arterial pressure (MAP) during the 1st mo after birth, pressor responses are unchanged, suggesting that vascular responsiveness is also unchanged. Alternatively, this could reflect increases in AVP metabolic clearance rate (MCR(AVP)). However, newborn AVP metabolism and synthesis are poorly studied. Therefore, we examined the pressor responses to infused AVP and the pattern of circulating AVP, AVP production rate (PR(AVP)), and MCR(AVP) in conscious newborn sheep (n = 5) at 9-38 days after birth. Basal MAP rose and heart rate (HR) fell during the study period (P < or = 0.02), while circulating AVP was unchanged (P > 0.1), averaging 3.01 +/- 0.86 pg/ml. Infused AVP elicited steady-state responses at 10-40 min, increasing plasma AVP and MAP and decreasing HR (P < 0.001). Although pressor responses were unchanged between 9 and 38 days, the rise in MAP correlated with increases in plasma AVP (R = 0.47, P = 0.02, n = 24). MCR(AVP) was unchanged throughout the 1st mo (P > 0.2), averaging 205 +/- 17 ml.kg(-1).min(-1), and was associated with an elevated PR(AVP), 973 +/- 267 pg.kg(-1).min(-1), which also was unchanged (P > 0.1). After birth, MCR(AVP) and PR(AVP) are elevated, probably accounting for the stable plasma AVP levels. The former is also likely to account for the stable pressor responses to infused AVP during the 1st mo. The reason for the elevated PR(AVP) is unclear but may relate to increases in vascular volume associated with postnatal growth. 相似文献
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Metabolism of Phosphatidylglycerol and Lysyl Phosphatidylglycerol in Staphylococcus aureus 总被引:3,自引:1,他引:2
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The metabolism of phosphatidylglycerol and lysyl phosphatidylglycerol was studied in Staphylococcus aureus under four conditions: growing at pH 7.0 and 5.2, and not growing (resting) at pH 7.0 and 5.2. Measurements of the amounts of phosphatidylglycerol and lysyl phosphatidylglycerol, as well as labeling and pulsechase experiments, revealed that the phosphate group of the former and the lysyl group of the latter were in a state of active turnover. A marked decline in the cellular level of phosphatidylglycerol observed when cells were resting at pH 5.2 was found to be caused by both a decrease in synthesis and an increase in catabolism. The level of lysyl phosphatidylglycerol was found to be relatively constant under the four incubation conditions, although the lysyl moiety was in a state of turnover. Experiments designed to test the possible role of lysyl phosphatidylglycerol as a lysyl group donor in biosynthetic processes or in lysine transport were negative; no evidence to support the hypothesis that lysyl phosphatidylglycerol serves as an intermediate was obtained. 相似文献
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Staphylococcus aureus ArcR controls expression of the arginine deiminase operon 总被引:1,自引:0,他引:1
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Makhlin J Kofman T Borovok I Kohler C Engelmann S Cohen G Aharonowitz Y 《Journal of bacteriology》2007,189(16):5976-5986
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黄鳝气呼吸代谢的研究 总被引:3,自引:0,他引:3
测定了黄鳝气呼吸状态下 ,2 5~ 2 7℃时的能量代谢情况。结果 ,表明平均耗氧率为 6 3 6 4mg/kg·h ,平均耗氧量 2 .81mg/尾·h ,体重与耗氧量之间的直线回归方程为 y =1.32 +0 .0 3x ;个体越大 ,耗氧量越大 ,个体越小 ,耗氧率越高。同时发现 ,黄鳝的耗氧率随环境温度变化及昼夜节律交替而变化。 相似文献
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