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Amino Acids: The Forum for Amino Acid, Peptide and Protein Research (v.13, #2)
Dietary tryptophan and aging by H. Sidransky M.D. (pp. 91-103).
This paper considers findings which may relate to whether there may be a correlation between dietary L-tryptophan and aging. Early studies had reported that animals fed a tryptophan-deficient diet showed increased longevity compared to controls. Although decreased serotonin levels due to the tryptophan-deficient diet was considered of importance for the increased longevity, a more likely explanation was decreased diet intake due to the deficient diet. Indeed, decreased diet consumption as well as decreased energy intake have been shown to lengthen the lifespan of animals. Greater quantitative assessment between the effect of a tryptophan-deficient diet and that of decreased energy intake needs to be obtained. Our recent findings that one mouse strain (NZBWF1), which is autoimmune susceptible and has a relatively short lifespan, demonstrate a significantly decreased binding affinity for L-tryptophan by hepatic nuclei when compared to other mouse strains are of much interest. These results stimulated us to reconsider the issue whether L-tryptophan itself may influence the aging process. Since L-tryptophan has a regulatory effect on hepatic protein synthesis which may be related to its binding to a specific nuclear receptor, much akin to what occurs with certain steroid hormones which are considered to be involved in the aging process, this review explores the possibility that L-tryptophan via its regulatory action may be of great importance and merits further investigation. This indispensible dietary component may have a vital regulatory control in the normal state and possibly also during the process of aging.
Interaction between taurine and angiotensin II: Modulation of calcium transport and myocardial contractile function by C. Ballard-Croft; M. S. Mozaffari; J. Azuma; S. Schaffer PhD (pp. 105-114).
Angiotensin II modulates several aspects of cardiac function, including myocardial contractility, heart rate and myocyte growth. Most of these actions are intimately associated with alterations in calcium transport. Since taurine also modulates calcium transport, we examined possible interactions between taurine and angiotensin II at the level of the major cellular extruder of calcium, the Na−-Ca2+ exchanger. Over a concentration range of 0.5–25 mM, Turne served as an effective inhibitor of angiotensin II-mediated stimulation of the exchanger. An Arrhenius plot of Na+-Ca2+ exchange activity revealed that angiotensin II (2 nM) increased transporter activity by reducing the activation energy of the transport process. Taurine (25 mM) inhibited the angiotensin II effect by partially preventing the reduction in activation energy. However, neither agent significantly altered the transition temperature, ruling out a change in membrane fluidity or an alteration in the rate limiting step of the transporter as a cause of the observed effects. Since the Na+-Ca2+ exchanger plays an important role in the handling of [Ca2+]i by the myocardium, the effect of taurine on angiotensin II's modulation of contractile function was also examined. Hearts perfused with buffer containing angiotensin 11 experienced a slight positive isotropic effect in the absence of taurine but this was converted to a negative inotropic effect in the presence of taurine. The data suggest that Turine inhibits some, but not all of the actions of angiotensin II. The possibility that a phosphorylation event is the site of the angiotensin II-taurine interaction is discussed.
Keywords: Amino acids; Taurine; Angiotensin II; α-Adrenergic agonists; Na−-Ca2+ exchange; Heart; Contraction
Analogues of taurine as inhibitors of the phosphorylation of an ≈20K molecular weight protein present in a mitochondrial fraction of the rat retina by J. B. Lombardini; C. Props (pp. 115-130).
It has been previously demonstrated that taurine inhibits the phosphorylation of an ≈20K apparent molecular weight protein present in the mitochondrial fraction of the rat retina (Lombardini, 1991). In the present studies, various analogues of taurine were tested for their inhibitory activity on the phosphorylation of this ≈20K protein. The most potent analogues were (±)trans-2-aminocyclopentanesulfonic acid (TAPS) and 1,2,3,4-tetrahydroquinoline-8-sulfonic acid (THQS) which were approximately 21 and 7 times more potent than the parent compound, taurine. Median-effect plots were used to calculate the inhibitory median effect and combination index values for the combined effects of taurine and taurine analogues. From these studies, it was determined that the inhibitory taurine analogues were antagonistic to taurine when used in combination with taurine to inhibit the phosphorylation of the ≈20K apparent molecular weight protein. It was also concluded that: 1) the distance between the nitrogen and sulfur atoms in the taurine structure was important for inhibitory activity; 2) if the nitrogen atom is either within or attached to an unsaturated ring structure the inhibitory potency was significantly decreased, and 3) if both the sulfur and nitrogen atoms are present within the ring structure the analogue has no activity.
Keywords: Amino acids; Taurine; Taurine analogues; Protein phosphorylation; Rat retina
Physical and structural properties of taurine and taurine analogues by J. D. Madura; J. B. Lombardini; J. M. Briggs; D. L. Minor; A. Wierzbicki (pp. 131-139).
In a variety of mammalian species it has been established that taurine is a necessary component of the visual system, however, the exact mechanism(s) as to the function of taurine is(are) elusive. Additionally, taurine is speculated to be a membrane stabilizer by interacting with phospholipids and a regulator of protein phosphorylation. Therefore the inhibition by taurine and taurine analogues of the phosphorylation of an ≈20 kDa protein present in the mitochondrial fraction of the rat retina has been investigated using computational methods. Correlations between molecular weight, molecular volume, and calculated pKa values vs. IC50 values are reported. These data appear to support the hypotheses according to Lombardini and Props that the inhibition of the phosphorylation of an ≈20kDa protein by taurine and taurine analogues is dependent on (i) the critical distance between the nitrogen and sulfur atoms in the taurine moiety (S-C-C-N) of the analogue; (ii) the environment of the nitrogen atom in the taurine analogue (saturated ring vs. unsaturated ring); and (iii) the placement of both the sulfur and nitrogen atoms not being present simultaneously in the ring structure. Using computational methods we present results that support hypotheses (i) and (ii).
Keywords: Amino acids; Taurine; pKa; LogP; Molecular modeling
Amino acids in honeybee worker haemolymph by K. Crailsheim; B. Leonhard (pp. 141-153).
In honeybee workers proline was the predominant amino acid and comprised from 50% in newly emerged bees up to 80% of total amino acids from the 3rd day on. The overall concentration averaged at about 20 mM in newly emerging bees, rose to a maximum of about 25mM at the 3rd–5th day and decreased in older bees. Essential amino acids decreased by 40% during the first 3 days and thereafter stayed constant. The bulk of amino acids with a lower concentration (from traces to about 2mM) showed either no change in concentration or was higher in newly emerging bees and decreased during the lifespan of the insects. Forager bees, collected after flight, had significantly lower proline concentrations as compared to 22 day old bees collected from the colony, while the concentrations of the bulk of all other amino acids did not change significantly. There was a great variance in the concentration of all amino acids between different colonies but we could not prove dependency on relatedness.
Keywords: Amino acids; Apis mellifera; Free amino acids; DABS-Amino acids; Haemolymph; Age dependency
A new synthesis of the tripeptide Gly-His-Lys with antimicrobial activity by Assoc. Prof. Dr. M. Liakopoulou-Kyriakides; C. Pachatouridis; L. Ekateriuiadou; V. P. Papageorgiou (pp. 155-161).
A new solid phase synthesis of the growth-modulating tripeptide Gly-His-Lys is described. 2-Chlorotrityl chloride resin and 9-fluorenylmethoxycarbonyl-(Fmoc), 4-methyltrityl-(Mtt) protecting groups were used. The synthetic tripeptide was tested for its activity against bacteria, yeast and fungi. The in vitro effect of the tripeptide on DNA, RNA and protein synthesis was studied as well.
Keywords: Amino acids; Tripeptide GHK; Synthesis; Antimicrobial activity
Identification ofS-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-3-mercaptopyruvic acid with a metabolic intermediate betweenS-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-l-cysteine andS-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-3-mercaptolactic acid by Dr. M. Kinuta; H. Shimizu; N. Masuoka; J. Ohta; W. -B. Yao; T. Ubuka (pp. 163-169).
S-[2-Carboxy-1-(1H-imidazol-4-yl)ethyl]-3-mercaptopyruvic acid (I) was chemically synthesized in 15% yield by incubating a reaction mixture oftrans-urocanic acid and 3-fold excess of 3-mercaptopyruvic acid at 45°C for 6 days. The synthesized compound was characterized by fast-atom-bombardment mass spectrometry and high-voltage paper electrophoresis. CompoundI was identified with a product of an enzymatic reaction ofS-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-l-cysteine (II) with rat liver homogenate in a phosphate buffer, pH 7.4. CompoundI was degraded toS-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-3-mercaptolactic acid (III), a compound previously found in human urine [Kinuta et al. (1994) Biochem J 297: 475–478], by incubation with rat liver homogenate. From these results, we suggest that compoundI is a metabolic intermediate for the formation of compoundIII from compoundII. The present pathway follows a formation of compoundII fromS-[2-carboxy-1-(1H-imidazol-4-yl)ethyl] gluthathione [Kinuta et al. (1993) Biochim Biophys Acta 1157: 192–198], a proposed metabolite ofl-histidine.
Keywords: Amino acids; Imidazole compound; Mercaptopyruvic acid; Urocanic acid; Histidine; Mass spectrometry; Paper electrophoresis
Synthesis of salicyl-peptides and their effect on human platelet aggregationin vitro by Dr. G. Stavropoulos; V. Magafa; M. Liakopoulou-Kyriakides; Z. Sinakos; A. Aaberg (pp. 171-181).
A series of leucine dipeptide amides containing at their N-terminal amino group the salicyl-residue [(o)-RO-C6H4-CO-, where R=H or CH3CO] have been synthesized by conventional solution techniques and tested for their inhibitory activity on human platelet aggregationin vitro induced by collagen, ADP or adrenaline. The salicyl-peptide (o)-HO-C6H4-CO-Leu-Asp(OBzl)-NH2 was found to exert strong inhibitory activity on platelet aggregation induced by collagen with an IC50 value 4.5 mM. The corresponding dipetide H2N-Leu-Asp(OVzl)-NH2 was also examined and was found to be less active, indicating that the presence of the lipophilicβ-benzyl ester group in combination with the salicyl group enhance the inhibitory activity. All the other salicyl-peptides examined either didn't show any inhibitory or aggregatory activity or a slight inhibition at the concentration of 9–10 mm.
Keywords: Amino acids; Collagen; Inhibitory activity; Platelet aggregation; Salicyl-peptides
Incorporation of nitrate nitrogen in rice seedlings transferred to anaerobic conditions by Dr. R. Reggiani; F. Bertini; M. Mattana (pp. 183-188).
Incorporation of15NO3- into amino acids was studied in 3-day-old aerobic rice seedlings (with coleoptile and root) subjected for 24h to anaerobic conditions. The incorporation of15N into glutamate, glutamine and alanine accounted for 89% and 84% of total incorporation in coleoptile and root, respectively. These findings indicate that, after the primary incorporation of15N into glutamate and glutamine, the main fate of nitrate nitrogen in rice seedlings subjected to anoxia is alanine.
Keywords: Amino acids; Anoxia; Coleoptile; Nitrate nitrogen; Rice; Root