Check out our New Publishers' Select for Free Articles

Amino Acids: The Forum for Amino Acid, Peptide and Protein Research (v.15, #4)

Recent advances in protein methylation: Enzymatic methylation of nucleic acid binding proteins by Dr. Sangduk Kim; G. H. Park; W. K. Paik (pp. 291-306).

Heterogeneous nuclear RNP protein A1, one of the major proteins in hnRNP particle (precursor for mRNA), is known to be post-translationally arginine-methylatedin vivo on residues 193, 205, 217 and 224 within the RGG box, the motif postulated to be an RNA binding domain. Possible effect of N^G-arginine methyl-modification in the interaction of protein A1 to nucleic acid was investigated. The recombinant hnRNP protein A1 wasin vitro methylated by the purified nuclear protein/histone-specific protein methylase I (S-adenosylmethionine:protein-arginine N-methyltransferase) stoichiometrically and the relative binding affinity of the methylated and the unmethylated protein A1 to nucleic acid was compared: Differences in their binding properties to ssDNA-cellulose, pI values and trypsin sensitivities in the presence and absence of MS2-RNA all indicate that the binding property of hnRNP protein A1 to single-stranded nucleic acid has been significantly reduced subsequent to the methylation. These results suggest that posttranslational methyl group insertion to the arginine residue reduces protein-RNA interaction, perhaps due to interference of H-bonding between guanidino nitrogen arginine and phosphate RNA.

Keywords: Protein-arginine methylation; Nucleic acid binding protein; Protein methylase I; S-adenosyl-L-methionine; RGG motiff

Epidermal growth factor (EGF) increases the renal amino acid transport capacity in amino acid loaded rats by Prof. Dr. Christian Fleck; J. Pertsch (pp. 307-320).

In anaesthetized adult female rats, the influence of epidermal growth factor (EGF) on renal amino acid handling was investigated in glutamine, arginine (both 50 mg/100 g b. wt. per hour), or alanine (90 mg/ 100 g b. wt. per hour) loaded animals. Continuous infusions of the three amino acids were followed by an increase in the fractional excretion (FE) of the administered amino acids as well as of the other endogenous amino acids. Under load conditions (alanine, arginine or glutamine), EGF pretreatment (8μg/100g b. wt. subcutaneously for 8 days, twice daily 8 a.m. and 4 p.m.) was followed by a stimulation of renal amino acid reabsorption. The increase in the fractional excretion of the administered amino acids was significantly lower than in non-EGF-treated rats. These changes in amino acid transport were connected with a significant reduction of GFR after EGF pretreatment (0.96 ± 0.10 vs. 0.62 ± 0.07 ml/min X 100 g b. wt.) and a distinct increase in sodium excretion (2.98 ± 0.55 vs. 4.97 ± 0.71μval/100 g b. wt. X 20 min). After loading with p-aminohippurate (PAH; 200mg/100g b. wt.), PAH excretion in EGF rats was increased by about 20%, whereas urinary protein excretion was lower in EGF pretreated rats (control: 0.45 ± 0.04 vs. EGF: 0.18 ± 0.03 mg/ 100 g b. wt. X 20 min). The PAH load reduced amino acid reabsorption as a sign of overloading of renal tubular transport capacity, but in EGF pretreated animals the amino acid excretion was only slightly increased under these conditions. Furthermore, EGF pretreatment depressed normal kidney weight gain significantly (874 ± 18 vs. 775 ± 32mg/100g b. wt.). EGF can improve the renal tubular transport capacity, but, compared to well-known stimulators of renal transport like dexamethasone or tri-iodothyronine, its effect is only of a moderate degree.

Keywords: Amino acid transport; Kidney; Epidermal growth factor; Amino acid load; Alanine; Arginine; Glutamine; p-Aminohippurate; Rats

Control of expression of the gene for the arginine transporter Cat-1 in rat liver cells by glucocorticoids and insulin by J. Liu; Maria Hatzoglou PhD (pp. 321-337).

Hepatic arginine and lysine uptake is partly regulated by changes in the transport activity of a group of cell surface proteins exhibiting properties of the transport system y⁺. TheCat-1 gene encodes a sodium-independent high-affinity cationic amino acid transporter of the y⁺ system which is nearly undetectable in the quiescent liver. In this paper we investigate the regulation of expression of Cat-1 in the quiescent rat liver by glucocorticoids and insulin, two hormones which play a critical role in amino acid dependent pathways of hepatic metabolism. Injection of insulin and glucocorticoids resulted in a rapid (15–30min, 4–5 fold) increase in transcription which returned to basal levels within 4 hours. In contrast to the rapid single peak of transcriptional induction of theCat-1 gene, the accumulation of the Cat-1 mRNAs occurred transiently with two peaks, the first at 30 minutes and the second at 2–4 hours following hormone treatment. These data indicate that expression of theCat-1 gene in the quiescent liver can be transiently induced by both transcriptional and post-transcriptional mechanisms. In FTO2B rat hepatoma cells, expression of the gene is constitutive and accumulation of Cat-1 mRNAs in response to dexamethasone and insulin was dependent on transcription and protein synthesis. Furthermore, the accumulation of the basal level of the Cat-1 mRNAs was reduced by 70%, upon treatment of cells with inhibitors of protein synthesis for 6h, when the transcription rate of the gene did not decrease significantly. We conclude the following: (i) under normal physiologic conditions, expression of theCat-1 gene in the quiescent liver is negligible, propably to prevent unnecessary transport and metabolism of arginine by the hepatic arginase in the hepatocytes. (ii) in the cases when hepatic cationic amino acid transport is needed, such as following feeding, cellular growth and illness, glucocorticoids and insulin induce expression of theCat-1 gene in liver cells through induction of transcription and stabilization of the mRNA. (iii) constitutive Cat-1 mRNA accumulation in rat hepatoma cells depends on protein synthesis through a labile regulated factor. Overall, constitutive expression of Cat-1 is associated with hepatic cellular growth and transformation.

Warm blood cardioplegia reduces the fall in the intracellular concentration of taurine in the ischaemic/reperfused heart of patients undergoing aortic valve surgery by R. Ascione; W. J. Gomes; G. D. Angelini; A. J. Bryan; M. -S. Suleiman (pp. 339-350).

The effect of cold and warm intermittent antegrade blood cardioplegia, on the intracellular concentration of taurine in the ischaemic/ reperfused heart of patients undergoing aortic valve surgery, was investigated. Intracellular taurine was measured in ventricular biopsies taken before institution of cardiopulmonary bypass, at the end of 30 min of ischaemic arrest and 20 min after reperfusion. There was no significant change in the intracellular concentration of taurine in ventricular biopsies taken after the period of myocardial ischaemia in the two groups of patients (from 10.1 ± 1.0 to 9.6 ±0.9μmol/g wet weight for cold and from 9.3 ± 1.3 to 10.0 ± 1.3μmol/g wet weight for warm cardioplegia, respectively). Upon reperfusion however, there was a fall in taurine in both groups but was only significant (P → 0.05) in the group receiving cold blood cardioplegia (6.9 ± 0.8μmol/g wet weight after cold blood cardioplegia versus 8.0± 0.8μmol/g wet weight following warm blood cardioplegia). Like taurine, there were no significant changes in the intracellular concentration of ATP after ischaemia in the two groups of patients (from 3.2 ± 0.32 to 2.95 ± 0.43μmol/g wet weight for cold and from 2.75 ± 0.17 to 2.62 ± 0.21μmol/g wet weight for warm cardioplegia, respectively). However upon reperfusion there was a significant fall in ATP in both groups with the extent of the fall being less in the group receiving warm cardioplegia (1.79 ± 0.19μmol/g wet weight for cold and 1.98 ± 0.27μmol/g wet weight for warm cardioplegia, respectively). This work shows that reperfusion following ischaemic arrest with warm cardioplegia reduces the fall in tissue taurine seen after arrest with cold cardioplegia. Accumulation of intracellular sodium provoked by hypothermia and a fall in ATP, may be responsible for the fall in taurine by way of activating the sodium/taurine symport to efflux taurine.

Keywords: Amino acids; Taurine; Aortic valve surgery; Cold and warm cardioplegia

Whole body autoradiographic study on the distribution of¹⁴C-d-serine administered intravenously to rats by Kazuhiro Imai Ph. D.; T. Fukushima; T. Santa; H. Homma; Y. Huang; M. Shirao; K. Miura (pp. 351-361).

The distribution of radioactivities in rats following intravenous administration of¹⁴C-d- or -l-serine was investigated by whole body autoradiography. The radioactivities were distributed throughout the whole body in both cases with the greatest amount being found in the pancreas. D- andl- Serine levels in the pancreas were determined by high-performance liquid chromatography with a chiral column which revealed, for the first time, the existence ofd-serine in the rat pancreas (12.6 ± 7.90 nmol/g wet tissue) together with a much higher concentration (924 ± 116 nmol/g) ofl-serine. The results suggested that exogenous D-serine of dietary origin contributed at least in part to the D-serine levels found in mammalian tissues.The accumulation of radioactivity in the kidney, especially in the corticomedullary area, even at 24 hr after administration of¹⁴C-l-serine suggested a possible link between acute necrosis of the renal proximal tubules and the administration of a large dose of D-serine [Am J Pathol 77: 269–282 (1974)].

Keywords: Amino acids; ¹⁴C-l-Serine; Rat; Whole body autoradiography; Accumulation; Kidney

Hypotaurine disproportionation reaction: Identification of products by Prof. S. Duprè; A. Spirito; F. Pinnen; K. Sugahara; H. Kodama (pp. 363-372).

Hypotaurine, concentrated under reduced pressure in HCl solution, partially (30–40%) degrades into taurine (about 30%), 2-aminoethyl-2-aminoethanethiolsulfonate (about 10%) and ethanolamine. The degradation products were identified using LC/APCI-MS, NMR, amino acid analysis and various chromatographics. The identities were confirmed by comparing the HPLS, MS and NMR characteristics of authentic compounds. One of the degradation processes during concentration of HCl solution of hypotaurine is therefore a disproportionation reaction which can interfere with the experimental results, when studying hypotaurine in biological systems.

Keywords: Amino acids; Hypotaurine; LC/APCI-MS chromatography; Disproportionation reaction; 2-Aminoethyl-2-aminoethanethiolsulfonate

Changes in urinary taurine and hypotaurine excretion after two-thirds hepatectomy in the rat by Henk S. Brand Ph.D.; G. G. A. Jörning; R. A. F. M. Chamuleau (pp. 373-383).

This study followed the time course of urinary taurine and hypotaurine excretion after two-thirds hepatectomy in rats. The excretion of both taurine and hypotaurine was elevated during 18th following the hepatectomy, with maximal excretion during the first 6h. Twelve and 24h after partial hepatectomy, the hepatic hypotaurine concentration was increased but liver taurine did not differ significantly from controls. No changes were observed in hypotaurine and taurine concentrations of heart, kidney, lung, muscle tissue and spleen. We postulate that partial hepatectomy induces a rapid increase of hepatic (hypo)taurine synthesis from precursor amino acids. The increased (hypo)taurine concentrations spill over into urine.

Keywords: Amino acids; Hepatectomy; Hypotaurine; Liver; Taurine; Urine

Free amino acid concentrations in milk: Effects of microwaveversus conventional heating by Dr Marie-Paule Vasson; M. -C. Farges; A. Sarret; L. Cynober (pp. 385-388).

Microwave effects on free amino acid concentrations in milkversus a water bath heating were investigated in view of their importance for infant growth. Concentrations of few amino acids, such as aspartate, serine or lysine, are unchanged whatever the way and the temperature of heating. In contrast, tryptophan concentrations decreased similarly whatever the way of heating (110 ± 3µmol/l before heatingvs 84 ± 4µmol/l after 30°C microwave heating, p < 0.05). On the contrary, concentrations of glutamate and glycine increased more after water bath heating at 90°C (325 ± 4 and 101 ± 1µmol/l, respectively) than after microwave heating (312 ± 4 and 95 ± 1µmol/l, respectively, p < 0.05) suggesting milk proteolysis. Moreover, the accumulation of ammonia observed at 90°C with the water bath together with increase Glu levels might reflect a degradation of glutamine. An ornithine enrichment, more evident with microwave heating, was shown and could be of interest as it is a polyamine precursor. Also, considering few variations of free amino acid concentrations and the time saved, microwave heating appears to be an appropriate method to heat milk.

Keywords: Free amino acids; Milk; Microwave; Water bath heating

Resolution of DL-2-aminosuberic acid via protease-catalyzed ester hydrolysis by M. Rivard; P. Maloň; Dr. V. Čeřovský (pp. 389-392).

Papain-catalyzed regioselective cleavage ofα-methyl ester in Z-DL-Asu(OMe)-OMe leads to Z-L-Asu(OMe)-OH and Z-D-Asu(OMe)-OMe. Subsequent saponifications yield Z-L-Asu-OH and Z-D-Asu-OH. The enzymaticα-ester hydrolysis was also achieved by subtilisin BPN′ in organic solvent with low water content.

Keywords: Amino acids; Aminosuberic acid; Enzymatic resolution; Papain; Subtilisin

Sections

Personal tools

Amino Acids: The Forum for Amino Acid, Peptide and Protein Research (v.15, #4)

Sections

Personal tools

Local resources

Amino Acids: The Forum for Amino Acid, Peptide and Protein Research (v.15, #4)