Cystine supplementation

Iriarte and Barnes (29) showed that cystine destruction by heat made this amino acidTirst limiting for the rat. However, cystine supplementation did not return the nutritional value to the optimum level. These workers were unable to determine the second limiting amino acid and could not rule out the possible development of a toxicity factor. Taira (30) determined that only cystine was destroyed under heating conditions commonly... 

Treatment in those patients who respond to pyridoxal phosphate is based on provision of approximately 250-500 mg per day. Folate deficiency may be avoided by the addition of 5 mg per day to this regimen. In patients who do not respond to the coenzyme, dietary manipnlation with a low methionine, cystine-supplemented diet may be helpfnl. Dipyridamole, an agent effective in decreasing platelet aggregation, has been nsed to prevent the thromboses, but there are no reports yet as to its effectiveness. 

In terms of amino acids bacterial protein is similar to fish protein. The yeast s protein is almost identical to soya protein fungal protein is lower than yeast protein. In addition, SCP is deficient in amino acids with a sulphur bridge, such as cystine, cysteine and methionine. SCP as a food may require supplements of cysteine and methionine whereas they have high levels of lysine vitamins and other amino acids. The vitamins of microorganisms are primarily of the B type. Vitamin B12 occurs mostly hi bacteria, whereas algae are usually rich in vitamin A. The most common vitamins in SCP are thiamine, riboflavin, niacin, pyridoxine, pantothenic acid, choline, folic acid, inositol, biotin, B12 and P-aminobenzoic acid. Table 14.4 shows the essential amino acid analysis of SCP compared with several sources of protein. 

The grain or pulse forms of legumes have a high total protein content (20-26%) and can therefore be used as a natural supplement to cereals. Pulses are normally deficient in the essential amino acids methionine and cystine but contain enough lysine, whereas cereals are deficient in lysine but contain enough methionine and cystine. 

A newer therapeutic approach is the administration of betaine (6-12 g daily), which lowers homocysteine levels by favoring remethylation [33], A theoretical hazard of betaine treatment is increasing the blood methionine, sometimes to an extravagant degree ( 1 mmol/1). Experience to date indicates that betaine administration is safe, with no major side effects except for a fishy odor to the urine. Other therapeutic approaches have included the administration of salicylate to ameliorate the thromboembolic diathesis. Patients also have been treated with dietary supplements of L-cystine, since the block of the transsulfura-tion pathway in theory could diminish the synthesis of this amino acid. 

By the 1930s many workers had shown that nutritionally inadequate proteins, such as zein from maize, could be effective as a source of nitrogen if supplemented by additional amino acids (for zein, tryptophan). Even if it contained all the essential amino acids, the amount of protein in the diet influenced the results. Osbome and Mendel found that if the diet contained 18% by weight casein, which is low in cystine, young rats grew, but if the amount of protein was diminished, added cystine was required to offset the relative deficiency of this amino acid. Later, after methionine had been discovered, it was shown to replace the need for cystine. 

Potatoes are an excellent source of carbohydrates and contain significant amounts ofphosphorus, potassium, calcium, and vitamins, especially vitamin C. Potato protein content, at over 10%, is relatively close to that of wheat flour (11%) also, thanks to their lysine, methionine, cystine and cysteine contents, potatoes are a valuable supplement to cereal proteins. For instance, potatoes provide a significant source of proteins (10-15% of total requirements), a major source of vitamin C, an important source of energy, and also minerals like iron and other vitamins such as thiamin, nicotinic acid, riboflavin, and pro-vitamin A (p carotene) (Salunkhe and Kadam, 1991). 

AAs methionine and cystine. Poor hatchability of fertile eggs can occur when diets of breeding hens are deficient in vitamin E. To prevent possible vitamin E deficiency, diets for growing poultry and breeding hens are usually supplemented with a source of vitamin E and possibly a suitable antioxidant. 

The metabolism of cystine and methionine. Availability of methionine in supplementing a diet deficient in cystine. Ibid., 98, 465 (1932). With R. W. Jackson. 

The in vitro gastric and intestinal digests of selenized yeast food supplements were investigated by successive HPLC-ICP-MS and HPLC-ES-MS/MS [51]. The main compound extracted by both gastric and intestinal juice was Se-methionine, which was also the main Se compound extracted by proteolytic digestion from the yeast supplements. Two other minor compounds could be identibed as Se-cystine and Se(0)-methionine, a degradation product of Se-methionine [51]. 

Moriarty-Craige, S. Adkison, J. Lyim, M. Gensler, G. Bressler, S. Jones, D. Stemberger, P. 2005. Antioxidant supplements prevent oxidation of cysteine/ cystine redox inpatients with age-related macular degeneration. Am. J. Ophthalmol. 140 1020-1026. 

The diet of industrialised countries is rich in proteins and provides the physiological amount of SAA needed for the turnover and synthesis of the proteins in the organism. The absorption of L-Cysteine/L-Cystine by the intestines, originated by a normal or supplemented diet, is practically total. The excess of Cys is known to be quickly catabolized [3] (Figure 2). 

The nutritional requirements for a certain metabolite, however, may also be influenced by the cell population density. For example, serine, cystine, glutamine and asparagine have been shown to be required at low, but not at high, cell densities (Eagle Piez, 1962). This occurs in situations when the newly synthesized metabolite is lost into the medium in amounts that exceed the biosynthetic capacity of the cell. The critical population density can be regarded as that which is able to condition the medium, i.e. to build up a concentration in equilibrium with the minimum effective intracellular level, before the cells die of the specific deficiency. At high cell densities, however, the cell culture medium can require supplementation with extra amino acids, in order to prevent their depletion. 

An effect of diet on BSP excretion has been observed in rats given a protein-free diet for 2 days (C29). Reduction in BSP excretion was accompanied by a decrease in glutathione content of the liver and a fall in conjugating enzyme activity which was restored by supplementing the protein-free diet with cystine. 

A number of possible solutions have been proposed to solve the problem, like the use of media supplemented with certain hormones (77), nicotinamide, or metyrapone, or media free of cystine and cysteine, but supplemented with aminolaevulinic acid (77). However, the application of such media has been a limited success since the apparently stable levels of cytochrome P-450 were accompanied by a selective change in the pattern of the different isoenzymes. A more promising approach appears to be the long-term cocultivation of hepatocytes with a rat epithelial cell-line, resulting in steady state levels of cytochrome P-450 after an initial decline (6, 18), However, the results of a recent study by Rogiers et al. (19), indicate that this technique does not offer a complete solution for the selective shift in the cytochrome P-450 isoenzyme patterns. 

Val-Cys-Ser-Leu-Tyr-Gln-Leu-Glu-Asn-Tyr-Cys-Asn-COO-. When only the composition is known (i.e., the sequence is unknown), the amino acids are separated by commas and enclosed in parentheses, for example, (Ala,Cys2,Gly) means a peptide containing one Ala, two Cys, and one Gly in an unknown order. A "polypeptide chain" is, by convention, a continuous chain linked only by peptide bonds. A protein may have only one polypeptide chain and then the polypeptide and the protein are synonymous. In other cases, a protein may have more than one polypeptide chain, as does insulin. In such cases, the different peptide chains within a protein may be held together by noncovalent forces, as in the case of hemoglobin, sometimes supplemented by covalent cystine cross links, as in the case of insulin. In many cases, the noncovalent interactions allow more than one conformation and a protein may switch from one conformation to another as part of its function. 

Awapara1623 observed an unknown 35S-cystine metabolite in the organs of rats. Cavallini and coworkers1626 have shown that this new metabolite is thiotaurine, NH2CH2CH2S02SH (197), which appears in the urine of rats fed a diet supplemented... 

By analogy with the effects of malnutrition and sulfur enrichment on the high-sulfur proteins of the keratin-associated proteins in wool fiber [44,45], these effects of a lower cystine content in hair are probably a result of a decreased synthesis of the sulfur-rich proteins because of malnutrition. Studies of the effects of diet in persons suffering malnutrition (i.e., protein deficiencies) show that diet supplementation can influence the protein composition of human hair. However, such effects have only been demonstrated among persons suffering from severe malnutrition and never among healthy persons on a normal diet see the section on the keratin-associated proteins of human hair later in this chapter. 

Among sheep with dietary insufficiencies, the minerals copper and zinc, when supplemented to the diet, have been shown to be important to wool fiber growth. Their effectiveness is attributed to the important roles these minerals play in sulfur amino acid metabolism copper serves to catalyze the oxidation of cysteine to cystine during fiber synthesis [109]. Zinc is required for cell division to occur, and it also appears to play a role in protein metabolism [110]. 

Cystine heart agar blood (CHAB) made of cystine heart agar (CHA Difco, Beckton Dickinson, Sparks, MD, USA) supplemented with 9% sheep blood. The sheep blood is chocolatized by adding it to autoclaved CHA before it cools below 75 °C. 

Supplement Vitamins and folate, L-cystine, and betaine Toxic metabolite Homocysteine... 

Supply adequate cystine (from medical food and/or supplements) [1],... 

Homocystinuria (pyridoxine nonresponsive) Cystathionine 6-synthase Homocystine in blood and urine, increased methionine and decreased cystine in blood Dislocated lenses, marfanoid-fike skeletal changes, intravascular thromboses, intellectual disabUity, osteopenia Methionine restriction cystine, betaine, and folate supplementation Betaine 100 mg/kg/ day oraUy... 

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