Studies on the Biochemistry of Sulphur: XII. Preliminary Studies on Amino-Acid Toxicity and Amino-Acid Balance on JSTOR
Our results demonstrate that a short segment containing positively charged amino acids at the N terminus of PrP plays an essential role in mediating PrP-related neurotoxicity. This finding identifies a protein domain that may serve as a drug target for amelioration of prion neurotoxicity. Proteins are made up of building blocks called amino acids.
Nevertheless the reason for such a long interest is that taurine acquired over the years a special appeal for its puzzling and multiple effects. We underlined the ability of taurine to control the function of ion channels and consequently membrane excitability as well as calcium homeostasis and excitation-contraction coupling. It has been highlighted that novel evidences are emerging regarding taurine mechanism of action, ranging from modulation of muscle metabolism to control of gene transcription, as well as in the specie-specific mechanisms underlying its intracellular levels in both chronic and acute conditions. These make the research on the topic â€œtaurine and skeletal muscleâ€ a continuous source of novel and exciting results allowing to renew the enthusiasm and novel working hypotheses.
However, whether the anti-inflammatory and anti-oxidant action contributes to the beneficial effect observed in dystrophic animals is not known yet and the evaluation of biomarkers in samples of taurine treated mdx mice will be useful at this regard. Our preliminary results favor a decrease in superoxide anion formation, measured by dihydroethidium staining, in tibialis anterior muscles of exercised mdx mice treated with taurine (De Luca, personal unpublished observations). An attractive hypothesis, currently under study in our laboratory, is that taurine may contrast the impaired SERCA activity in dystrophic muscle either directly or by reducing the damaging effect brought about by oxidation and/or nitrosylation [13, 54, 106].
These results reinforce the original data of Huxtlable and Bressler about the ability of taurine to stimulate calcium uptake by vesicles of SR . Recent insight into the role of taurine in skeletal muscle has been obtained by the group of Hayes, who supplemented rats with taurine and evaluated the outcome on various functional parameters . Taurine supplementation significantly increases the amino acid content in skeletal muscle, without any adaptive change in TauT activity; in parallel an increase in force and a greater resistance and recovery after fatigue have been observed. These changes were paralleled by an increase in calsequestrin1, the calcium binding protein that works to maintain high amounts of calcium in the cysterna of SR.
Branched-chain amino acids stimulate the building of protein in muscle and possibly reduce muscle breakdown. Branched-chain amino acids seem to prevent faulty message transmission in the brain cells of people with advanced liver disease, mania, tardive dyskinesia, and anorexia. It is therefore evident that taurine is essential to maintain muscle performance and excitation-contraction coupling; however the mechanism for these actions is still unclear.
Some potential toxins may be passed along a food chain via animal intermediates. The increased interest in herbal medicines in the Western countries will increase exposure to such compounds. The amino group contains nitrogen, which exists in the form of ammonia after it’s cleaved from the original amino acid. This toxic ammonia must be removed from the body, so it binds with another amino acid, then goes to the liver.
Amino acids have various properties that can affect the shape of the protein or influence its function. One amino acid called tyrosine is able to form links to other tyrosines. These links can bond two proteins together. One thing that helps tyrosine to form these links is a process known as oxidative stress, which is known to damage cells via the release of harmful molecules called free radicals.
In the EDL muscle of aged rats supplemented with taurine an almost complete recovery of the pharmacological sensitivity of gCl to either direct and indirect channel modulators, such as the enantiomers of p-chloro-phenoxy propionic acid and the phorbol esters, respectively, was observed. The effect of these latter, along with the amelioration of mechanical threshold observed, discloses the ability of taurine to modulate gCl by reducing the phosphorylation state of the chloride channel brought about by calcium and phospholipid-dependent protein kinase C [83, 84]. This offers a unifying mechanism for physiological taurine action via calcium homeostasis and modulation of calcium-dependent signaling pathways. Our research has shown that taurine, acutely applied in vitro, exerts a concentration-dependent increase of gCl in rat extensor digitorum longus (EDL) myofibers, and in parallel reduces membrane excitability [28, 29].
- Taking branched-chain amino acids for up to 6 months seems to improve attention in children with phenylketonuria.
- This is different than protein poisoning.
- Cysteine sulfinic acid is then decarboxylated to hypotaurine by the cystyeine sulfinate decarboxylase.
- Supplement of methionine to the high tyrosine diet partially alleviated both growth depression and pathological lesions.
However, the optimal dose of taurine is yet to be agreed upon and research does not clearly indicate how much an individual needs to reap the benefits, without experiencing toxic effects of the amino acid. As a result, the health industry has responded with various supplementation products that allow individuals to increase their daily intake of taurine and other amino acids beyond normal dietary intake. Some of the risks associated with high amino acid consumption come from the high-protein diet that supplies them.
Similar results were obtained when localization and biochemical analyses were performed on Î”23-134 PrP expressed in transfected HEK and N2a cells (data not shown), as well as in cerebellar granule neurons cultured from Tg(Î”23-134) mice (Fig. 5J-M). Lysine is an essential amino acid in human nutrition because the body cannot produce it; therefore, it must be taken in either by diet or supplementation. Lysine was first isolated from casein (a milk phosphoprotein) in 1889. It was first introduced in the United States as lysine hydrochloride in 1955. There was an interest in fortifying bread with lysine to target populations with lysine-poor diets.
There are conflicting results about the effects of branched-chain amino acids in people with a disease of the spine called SCD. Some early research suggests that taking branched-chain amino acids by mouth might improve some symptoms of SCD. However, other research suggests that branched-chain amino acids do not improve muscle control in people with SCD. The object of this study was to determine the effects of individual amino acid supplements on the development of tyrosine toxicity in growing rats fed 10% casein containing 5% tyrosine. Each amino acid was added at levels equivalent to its content in 20% casein.
Many hospitals may use total parenteral nutrition solutions that lack branched-chain amino acid. In addition, insulin may be used to stimulate a metabolic process known as anabolism.
In young rats on low-protein diets, depression of growth and food intake occur when additional tyrosine is given, which is followed by death at higher tyrosine intake levels. A unique effect of this amino acid is to induce corneal and paw lesions in rats fed low-protein diets with 3-5% tyrosine, but histopathological changes also occur in a variety of other tissues (1). These effects are moderated with time and higher levels of dietary protein or by limiting amino acids (1). The eye lesions were shown to consist of tyrosine crystals resulting from the high concentration and low solubility of tyrosine in tissue fluids (111,112). In addition, changes in catecholamine-mediated functions, e.g., blood pressure, were reported (113).