Effect of amino acid imbalances on the stimulatory effect of L-tryptophan on hepatic protein synthesis

Summary Earlier it was reported that mice or rats tube-fed a single feeding of L-tryptophan (TRP) demonstrated a stimulation of hepatic protein syn thesis. The present study was concerned with whether dietary imbalances induced by tube-feeding different ratios of L-alanine (ALA) or L-leucine (LEU) in relation to TRP would affect TRP's stimulatory effect on hepatic protein synthesis. Male Swiss mice, food-deprived overnight, were tube-fed one feeding of solution keeping TRP constant and varing ratios of ALA/TRP of 0.4, 2.1, or 4 or ratios of LEU/TRP of 4.8, 7.2, or 9.6. After 1 h, mice were killed and protein synthesis (¹⁴C-leucine incorporation into proteins in vitro using microsomes of livers) was measured. TRP alone stimulated hepatic protein synthesis by 83 % while ALA/TRP ratios of 2.1 or 4 but not of 0.4 and LEU/TRP ratios of 9.6 but not of 4.8 or 7.2 caused significant decreases in the stimulation of hepatic protein synthesis. Measurements of serum and hepatic free TRP concentrations in the experimental groups were similar in all groups tube-fed TRP alone or in combinations.This study was supported by U.S. Public Health Service Research Grant DK-45353 from the National Institute of Diabetes and Digestive and Kidney Diseases.     

Effect of glucosamine on amino acid transport and intensity of protein synthesis in liver cells in an inflammation model

The effect of glucosamine on the transport of amino acids and protein synthesis in hepatocytes when modelling inflammation was studied. It was found the considerable decrease of the amino acid transport via hepatocyte membranes. The protein synthesis intensity was displayed as also significantly reduced. Administration of glucosamine to the rats normalized both studied processes.     

Total amino acid stabilization during cell-free protein synthesis reactions

Limitations in amino acid supply have been recognized as a substantial problem in cell-free protein synthesis reactions. Although enzymatic inhibitors and fed-batch techniques have been beneficial, the most robust way to stabilize amino acids is to remove the responsible enzymatic activities by genetically modifying the source strain used for cell extract preparation. Previous work showed this was possible for arginine, serine, and tryptophan, but cysteine degradation remained a major limitation in obtaining high protein synthesis yields. Through radiolabel techniques, we confirmed that cysteine degradation was caused by the activity of glutamate-cysteine ligase (gene gshA) in the cell extract. Next, we created Escherichia coli strain KC6 that combines a gshA deletion with previously described deletions for arginine, serine, and tryptophan stabilization. Strain KC6 grows well, and active cell extract can be produced from it for cell-free protein synthesis reactions. The extract from strain KC6 maintains stable amino acid concentrations of all 20 amino acids in a 3-h batch reaction. Yields for three different proteins improved 75-250% relative to cell-free expression using the control extract.     

Regulation of protein synthesis inEscherichia coli by amino acid analogues

Эффект phenylserine, аналоговый от Фенилаланин, и по proteosynthesis на создание искусственных β-galactosidase был изучен в разных штаммов Escherichia коли-либо аминокисл от. Было установлено, что в Escherichia титр сер (вс-gly) вс-phenylserine препятствует включе нию от аланин и β-galactosidase формирование в присутствии этих важнейших аминокислот. В среднесрочной его недостатками стимулируется как включение и β-galactosidase синтез. Включение аминокисл от и формирование энзима не были затронуты в Escherichia титр phe-в полной средой. В недостаткам и среднего phenylserine увеличился регистра ции, но не влияет на β-galactosidase синте за. Было также установле но, что phenylserine-1-14C была включена в белк и из Escherichia коли-phe. Стимуляторы эффект в phenylserine Escherichia титр услуг, gly-было расследовано и было установлено, чт о аналог было разбито и benzaldehyde глицин. Механизм действия эт ого Аналог на разных в идов недостатками мутантов из Escherichia коли обсуждается.     

Relationship between carbon source and susceptibility of Cephalosporium acremonium to selected amino acid analogues

The susceptibility of Cephalosporium acremonium to selected amino acid analogues was markedly influenced by the carbon source used in the test media. Lysine hydroxamate, beta-hydroxy norvaline, and hexafluorovaline were toxic when tested with ribose, ribose or fructose, and ribose or galactose, respectively. In contrast, thialysine and thiaisoleucine inhibited C. acremonium with glucose, fructose, galactose, sucrose, mannitol, sorbitol, and soluble starch. Neither of these analogues was toxic at levels tested when glycerol was used as a carbon source. The minimal inhibitory concentrations (MIC) of thialysine, homoserine, and alpha-methylserine were greater than 1000, greater than 1000, and 250 microgram/mL, respectively, with glycerol. In contrast, the MIC values for the same three analogues were 31, 62, and 125 microgram/mL, respectively, with mannitol. The matching of the carbon sources with the specific amino acid analogues expands the number of analogues useful for selecting derepressed mutants. Thialysine-resistant mutants (tlysR) of C. acremonium which excrete lysine were isolated on a medium containing mannitol.