Escherichia coli leucyl-tRNA synthetase (LeuRS) is one of aminoacyl-tRNA synthetases (aaRSs) and belongs to class 1 aaRSs. The apparent steady-state kinetics of the aminoacylation reaction catalyzed by LeuRS in the pr...Escherichia coli leucyl-tRNA synthetase (LeuRS) is one of aminoacyl-tRNA synthetases (aaRSs) and belongs to class 1 aaRSs. The apparent steady-state kinetics of the aminoacylation reaction catalyzed by LeuRS in the presence of some RE3+ were studied. The results show that Mg2+ can be substituted by RE3+ for the aminoacylation reaction. The apparent K-m values for ATP and leucine are markedly different between native and Mg2+-free tRNA(1)(Leu). At high concentration of ATP there is inhibitory effect on Mg2+-free tRNA but not on native tRNA, which indicates that metal ions are a substrate of the aminoacylation reaction.展开更多
Dihydroxyacid dehydratase (DHAD), the rate-limiting enzyme in the synthesis of branched-chain (BCA) amino acids in bacteria and plants, is sensitive to oxyradical toxicity. Oxidant stress reversibly inactivates DHAD a...Dihydroxyacid dehydratase (DHAD), the rate-limiting enzyme in the synthesis of branched-chain (BCA) amino acids in bacteria and plants, is sensitive to oxyradical toxicity. Oxidant stress reversibly inactivates DHAD and causes starvation for BCA and reversible cessation of growth in Escherichia coli [1][2]. To better understand the underlying toxicity mechanisms, we have determined the cellular concentrations of charged-tRNAs for BCA, in E. coli treated with the redox-active chemical, paraquat. Contrary to expectation, in the paraquat-treated cells, the concentration of only charged leucyl-tRNA decreased dramatically;whereas, the concentrations of the other BCAs (valine and isoleucine) increased. This paradoxical result, the “paraquat effect” can be best explained if leucine is the most abundant amino acid in the E. coli proteins and therefore the rate-limiting building block in their synthesis. Based on this assumption, we investigated the concentration of free amino acids in E. coli and their relative abundances in E. coli proteins. Protein amino acid frequencies were determined by analyzing one-hundred gene bank protein sequences with software developed as described in Methods. Leucine is the most abundant amino acid in the E. coli proteins (10%) and consequently, the cellular free leucine concentration is smaller and the native charged-leucyl-tRNA levels are much higher than those of valine and isoleucine. This has relevance to humans because: leucine-deprivation was shown to be beneficial in tumor suppression [3], and leucine-supplementation was beneficial in the recovery from exercise-induced muscle loss [4][5], and leucine also occurs at a higher frequency in almost all human proteins. In three human protein categories, we examined it ranged from 9% to 17%. This predominance of leucine in proteins would make cells vulnerable to impairment of the leucine pools and could explain our results in E. coli and some of the biological effects of free leucine in humans.展开更多
AIM: To investigate the effect of adrenalectomy (ADX) on the epididymidis of Sprague-Dawley rats. METHODS: The histological, biochemical (cholesterol protein, zinc, copper, alkaline and acid phosphatase aryl sulphatas...AIM: To investigate the effect of adrenalectomy (ADX) on the epididymidis of Sprague-Dawley rats. METHODS: The histological, biochemical (cholesterol protein, zinc, copper, alkaline and acid phosphatase aryl sulphatase, lactic dehydrogenase and leucine amino peptidase) and hormonal (FSH, LH and testosterone) changes of caput and cauda epididymis in ADX rats were observed. RESULTS: Organ wet weight, histological studies and morphometric measurements indicated a cellular degeneration in caput and cauda epididymis of ADX rats. Serum testosterone level was significantly lower in ADX than in sham-operated rats, while the serum FSH and LH were below the detection limit of 1 mIU/mL. The enzymatic activity was higher in ADX than in sham-operated rats. Epididymal zinc level increased whereas copper level decreased in ADX rats compared to the sham-operated. CONCLUSION: Adrenalectomy leads to degeneration of caput and cauda epididymidis epithelial cells as a result of decreased supply of testosterone.展开更多
文摘Escherichia coli leucyl-tRNA synthetase (LeuRS) is one of aminoacyl-tRNA synthetases (aaRSs) and belongs to class 1 aaRSs. The apparent steady-state kinetics of the aminoacylation reaction catalyzed by LeuRS in the presence of some RE3+ were studied. The results show that Mg2+ can be substituted by RE3+ for the aminoacylation reaction. The apparent K-m values for ATP and leucine are markedly different between native and Mg2+-free tRNA(1)(Leu). At high concentration of ATP there is inhibitory effect on Mg2+-free tRNA but not on native tRNA, which indicates that metal ions are a substrate of the aminoacylation reaction.
文摘Dihydroxyacid dehydratase (DHAD), the rate-limiting enzyme in the synthesis of branched-chain (BCA) amino acids in bacteria and plants, is sensitive to oxyradical toxicity. Oxidant stress reversibly inactivates DHAD and causes starvation for BCA and reversible cessation of growth in Escherichia coli [1][2]. To better understand the underlying toxicity mechanisms, we have determined the cellular concentrations of charged-tRNAs for BCA, in E. coli treated with the redox-active chemical, paraquat. Contrary to expectation, in the paraquat-treated cells, the concentration of only charged leucyl-tRNA decreased dramatically;whereas, the concentrations of the other BCAs (valine and isoleucine) increased. This paradoxical result, the “paraquat effect” can be best explained if leucine is the most abundant amino acid in the E. coli proteins and therefore the rate-limiting building block in their synthesis. Based on this assumption, we investigated the concentration of free amino acids in E. coli and their relative abundances in E. coli proteins. Protein amino acid frequencies were determined by analyzing one-hundred gene bank protein sequences with software developed as described in Methods. Leucine is the most abundant amino acid in the E. coli proteins (10%) and consequently, the cellular free leucine concentration is smaller and the native charged-leucyl-tRNA levels are much higher than those of valine and isoleucine. This has relevance to humans because: leucine-deprivation was shown to be beneficial in tumor suppression [3], and leucine-supplementation was beneficial in the recovery from exercise-induced muscle loss [4][5], and leucine also occurs at a higher frequency in almost all human proteins. In three human protein categories, we examined it ranged from 9% to 17%. This predominance of leucine in proteins would make cells vulnerable to impairment of the leucine pools and could explain our results in E. coli and some of the biological effects of free leucine in humans.
文摘AIM: To investigate the effect of adrenalectomy (ADX) on the epididymidis of Sprague-Dawley rats. METHODS: The histological, biochemical (cholesterol protein, zinc, copper, alkaline and acid phosphatase aryl sulphatase, lactic dehydrogenase and leucine amino peptidase) and hormonal (FSH, LH and testosterone) changes of caput and cauda epididymis in ADX rats were observed. RESULTS: Organ wet weight, histological studies and morphometric measurements indicated a cellular degeneration in caput and cauda epididymis of ADX rats. Serum testosterone level was significantly lower in ADX than in sham-operated rats, while the serum FSH and LH were below the detection limit of 1 mIU/mL. The enzymatic activity was higher in ADX than in sham-operated rats. Epididymal zinc level increased whereas copper level decreased in ADX rats compared to the sham-operated. CONCLUSION: Adrenalectomy leads to degeneration of caput and cauda epididymidis epithelial cells as a result of decreased supply of testosterone.
