Serum cystine

In the second Test Series, the supply of methionine was decreased to 71 mg per kg and that of phenylalanine to 93 mg per kg. Simultaneously, 8.5 mg of cystine per kg and 20 mg of tyrosine per kg were added to the amino acid solution. This resulted in a lesser rise in serum methionine concentration than observed in the first Test Series. At the same time, the rapid induction of counter-regulatory processes, observed before, failed to appear so that the serum methionine concentrations in the second Test Series were still increased at the end of the tenth day of infusion. In the second Test Series, the serum cystine concentrations were slightly higher than those of the first Test Series. A further reduction of methionine supply is planned. Cystine itself does not seem to be necessary. VJhen the supply of phenylalanine was reduced, the serum concentrations of this amino acid showed a smaller increase in the second Test Series as compared with the first Test Series. 

Investigations of the effects of UV- and hypochlorite-induced oxidative modification of 20 amino acids and human serum albumin (HSA) on their antiradical properties showed unexpected results [36], Seven amino acids (cystine, histidine, methionine, phenylalanine, serine, tryptophan, and tyrosine) and HSA developed ACW following oxidation (see examples in Fig. 14). The fresh (produced in 1998) HSA from Serva had no antiradical capacity, but it acquired this quality during irradiation. The out-of-date HSA sample (Dessau, GDR, 1987, expiration date 7/1/1992) showed a remarkable ACW even in an unirradiated state. 

Disulfide bonds confer additional stability. A frequently encountered structural component is the sequence —Cys—Cys— with both residues forming disulfide bonds with other cystines. This is a useful architectural unit and forms the basis for linking three different chain segments in close proximity. This structure is found in serum albumin. 

Bovine serum albumin 2 66,267 4.7-4.9 Rod-shaped protein, containing one cysteine and 17 cystine residues Partial unfolding at low (<4) and high (>8) pH values... 

One of the hallmarks of OBPs is the six cysteine (six half cystines) residues, but this criterion alone is not sufficient to classify a certain protein as olfactory protein. It is important to demonstrate that an OBP is expressed only (or predominantly) in olfactory tissues. Evidence for their ability to bind odorants is also desirable, but not sine qua non. One of these criteria alone would not be enough to define a given protein as an OBP. For example, bovine serum albumin (BSA) binds to insect pheromones (Leal, unpublished data) and yet it is not an OBP because it does not occur in olfactory tissues in the first place. Conversely, a protein specific to antennae is not necessarily an OBP. There are other proteins that may be expressed in antennae but not in control tissues. Non-OBPs specific to insect antennae have been previously detected (Ishida and Leal, unpublished data). Also, a g lu tath i o n e -. S -1 ra n s I e ra s e has been reported to be expressed specifically in antennae of M. sexta (Rogers et al., 1999). Likewise, the six-cysteine criterion should not be misleadingly used. Insulin and bovine pancreatic trypsin inhibitor, for example, have six cysteines in three disulfide bridges and yet they are not odorant-binding proteins. Also, mammalian and insect defensins have six well-conserved cysteine residues. 

Figure 2. SDS gel electrophoresis of the products of partial cystine cleavage for several test proteins. A. molecular weight standards, B. yeast alcohol dehydrogenase. C. P-lactoglobulin, D. hen egg lysozyme, E. ovalbumin, F. calf fetal serum fetuin. Molecular weight standards are indicated by arrows on the left side of the gel and are bovine serum albumin (66,300), bovine liver glutamate dehydrogenase (55,400), porcine muscle lactate ddiydiogenase (36,500), bovine erythrocyte carbonic anhydrase (31,000), soybean trypsin inhibitor (21,500), hen egg lysozyme (14,400), bovine lung aprotinin (6,000), unresolved bovine pancreatic insulin A and B chains.

Oxidation at solid electrodes. Oxidation of cysteine, cystine and both forms of glutathione at a platinum electrode was studied extensively by Pradac, Koryta and Ossendorfova [158-160]. The oxidation of these substances occurs by reaction of the adsorbed radical with a surface oxide. Therefore, the calibration curve approaches a limiting value at higher concentrations. Reproducible results are obtained at pH 7.2 using cyclic voltammetry. This method makes it impossible to estimate these substances in blood serum [161, 162] and in some body organs [161,163]. Cysteine as electrochemical indicator can also be determined in vivo after intravenous injection, as for example in the assessment of the blood supply to the kidney [164-166]. 

Farrelly and Watkins (F4) have used high voltage electrophoresis of unmodified urine or deproteinized serum for the rapid separation of fourteen amino acids in one direction on a thin-layer plate. Evered and Dando (E16) have employed low voltage electrophoresis for one way separation of amino acids on Whatman No. 1 paper using various buffer solutions. They stated that only the acidic and basic amino acids, p-amino acids, and cystine could be separated completely from a complex mixture such as blood or urine. Scherr (SIO) and Stevens (S52) have also used low voltage electrophoresis for the unidirectional separation of amino acid mixtures on cellulose acetate strips. 

Wilson s disease or ceruloplasmin deficiency (autosomal recessive) Excess secretion of glycine, serine, and cystine Lenticular degeneration, positive copper balance, low serum ceruloplasmin levels, and defects in renal tubular reabsorption Mental retardation, ataxia, extrapyramidal symptoms, and cirrhosis Chromatography low blood and high urine copper levels low serum cemlc Iasmin (B8. H18. H19, PU. S9, W16)... 

As expected, there are species variations in amino acid composition. For horse serum cholinesterase, the three sets of results (from two independent laboratories) are in very satisfactory agreement, with estimates for only four of the amino acids differing substantially. In all five sets, aspartic and glutamic acids occur in nearly equal amounts, and together account for about 20% of the amino acid content of the molecule. In a subunit of molecular mass 80,000 daltons, there would be about 540 amino acid residues, which would indicate that 100 to 110 of these would be either aspartic acid or glutamic acid. At the other extreme, histidine, methionine, and half-cystine together represent only 6% of the amino acids. 

Because a colorimetric screening test for urinary homocystine was positive, the doctor ordered several biochemical studies on Homer Sistine s serum, which included tests for methionine, homocyst(e)ine (both free and protein-bound), cystine, vitamin B12, and folate. The level of homocystine in a 24-hour urine collection was also measured. 

The results were as follows the serum methionine level was 980 p,M (reference range, <30) serum homocyst(e)ine (both free and protein bound) was markedly elevated cystine was not detected in the serum the serum B12 and folate levels were normal. A 24-hour urine homocystine level was elevated. 

If the blood levels of methionine and homocysteine are very elevated and cystine is low, cystathionine p-synthase could be defective, but a cystathionase deficiency is also a possibility. With a deficiency of either of these enzymes, cysteine could not be synthesized, and levels of homocysteine would rise. Homocysteine would be converted to methionine by reactions that require B12 and tetrahydrofolate (see Chapter 40). In addition, it would be oxidized to homocystine, which would appear in the urine. The levels of cysteine (measured as its oxidation product cystine) would be low. A measurement of serum cystathionine levels would help to distinguish between a cystathionase or cystathionine p-synthase deficiency. 

Metabolic effects include interference with the biosynthesis of cystine and cholesterol, depression and stimulation of phospholipid synthesis and, at higher concentrations, inhibitions of serotonin oxidation. A 1981 study did not reveal any decrease in serum cholesterol or increase in serum triglycerides (Kiviluoto et al., 1981). 

Sodium hydride in DMSO is an effective medium for the reduction of disulfide bonds in proteins under aprotic conditions. When the molar ratio of hydride to 1/2 cystine residues exceeds 2 1, essentially complete reduction of the disulfide bonds of bovine serum albumin is achieved. 

An interesting aspect is gained from checking the content of cystine in hydrolysates of sera obtained from both healthy and diseased persons. In disease the cysteine content in the serum is decreased, as has been shown in patients suffering from carcinoma (43). There exists a parallel with the protein content, and therefore this state may express hypo-proteinemia and may be due to a decrease of albumin alone, even if globulins are simultaneously normal or moderately increased, since the cysteine content in human albumin is more than twice as high as that in human globulin. 

Calibrate using cystine solutions prepared by dissolving it in IN NH solution in concentrations of 2, 4, 6, 8 and 10 mg/100 ml, polarographing them in the same volumes as urine or serum appropriately diluted. Such a calibration, however, is not sufiicient for the determination of cystine in hydrolysates in which the presence of some other amino acids (e.g.,... 

A. Modification of the Cystine Residues in Bovine Serum Albumin... 

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