Cysteine plasma concentration

Cilastatin prevents the metabolism of imipenem by renal tubular dipeptidase, which also hydrolyses the glutathione metabolite cysteinylglycine. In patients taking imipenem + cilastatin, plasma concentrations of cysteinylglycine were significantly increased, while cysteine concentrations fell and homocysteine concentrations were unchanged (483). The clinical significance of this is not clear. 

Taurine is a dietary essential in the cat, which is an obligate carnivore with a limited capacity for taurine synthesis from cysteine. On a taurine-free diet, neither supplementary methionine nor cysteine will maintain normal plasma concentrations of taurine, because cats have an alternative pathway of cysteine metabolism reaction with mevalonic acid to yield felinine (3-hydroxy-1,1-dimethylpropyl-cysteine), which is excreted in the urine. The activity of cysteine sulfinic acid decarboxylase in cat liver is very low. 

The biochemical phenotype of homocystinuria is characterized by increased plasma concentrations of methionine, free homocysteine and cysteine-homocysteine disulfide, together with low cystine (Figure 55-6, C). Determination of total homocysteine after treatment of the sample with... 

Ascorbate could enhance delivery of NO to the vascular wall from plasma. Where measured concentrations of NO in plasma are about 3 nM (Stamler et al. 1992), NO can be carried as an S-nitrosothiol on albumin and free cysteine (Keaney et al. 1993). The plasma concentration of such S-... 

Distribution. Lead in blood partitions between plasma and red blood cells, with the larger fraction (90-99%) associated with red blood cells (Cake et al. 1996 DeSilva 1981 Everson and Patterson 1980 Manton and Cook 1984 Ong and Lee 1980a). Lead in plasma binds to albumin and y -globulins (Ong and Lee 1980a). The fraction that is not bound to protein exists largely as complexes with low molecular weight sulfhydryl compounds these may include cysteine, homocysteine, and cysteamine (Al-Modhefer et al. 1991). Approximately 75% was bound to protein when whole human blood was incubated with 50 ig/dL lead (as lead chloride) approximately 90% of the bound lead was associated with albumin (Ong and Lee 1980a). However, the fraction of lead in plasma bound to protein would be expected to vary with the plasma lead concentration. 

ROS can modify amino acid side chains, with histidine, tryptophan, cysteine, proline, arginine, and lysine among those most susceptible to attack (Brown and Kelly 1994). As a result, carbonyl groups are generated, and these carbonyl concentrations can be measured directly in plasma by using atomic absorption spectroscopy, fluorescence spectroscopy, or HPLC following reaction with 2,4-dinitrophenylhydrazine. 

Ceftiofiir is absorbed poorly after oral administration but rapidly after intramuscular injection. In all species, ceftiofur was rapidly metabolized to desfuroyl-ceftioftir and fiiroic acid. Desfiiroylceftiofur occurred in the free form in the plasma of treated cattle but was covalently bound to plasma proteins in rats (82). Maximum blood concentrations of ceftiofiir-related residues were achieved within 0.5 and 2 h of dosing. Unmetabolized ceftiofur was generally undetectable in blood within 2-4 h of dosing (83). More than 90% of the administered dose was excreted within 24 h of administration, mostly in urine. Residues in urine and feces were composed primarily of desfiiroylceftiofur and desfiiroylceftiofur cysteine disulfide, with small amounts of unmetabolized ceftiofur. 

After intramuscular injections of radiolabeled ceftiofur to cattle and swine, the compound was absorbed rapidly into the blood and eliminated mostly in urine (84). The tissue in which highest residue concentrations were observed at 12 h after the last dose was the kidney. Most of the radioactivity was found in the form of the microbiologically active primary metabolite, desfiiroylceftiofur, conjugated to macromolecules in plasma and tissues. Desfiiroylceftiofur cysteine was also found in tissues, plasma, and urine, whereas the desfiiroylceftiofur dimer was found in urine. It was suggested that since the binding of desfiiroylceftiofur to biological molecules is reversible, all of the ceftiofiir-related residues that contain the desfuroylceftiofur moiety have the potential to be microbiologically active. 

In rats receiving [ Cjbenzyl chloride in corn oil by gavage, the peak plasma level was reached after 30 min. The distribution half-life was 1.3 h, while the elimination half-life was 58.5 h. After 48 h, the higher concentrations were found in the stomach, gastric contents, ileum and duodenum, followed by liver, adrenal, bone marrow and blood. After 72 h, approximately 76% was excreted in urine and, in expired air, 7% as 002 and less than 1.3% as benzyl chloride or its metabolites. Urinary metabolites were identified as Y-benzyl-A-acetyl cysteine, benzx l alcohol and benzaldehyde (Saxena Abdel-Rahman, 1989). 

One other serious criticism regarding the data on Cu speciation is the neglect of the cysteine present in blood plasma. Cu11 and cysteine undergo a facile redox reaction (Chapter 20.2). Since the reaction is irreversible, no quantitative thermodynamic quotient is available for use in the computer calculations. Another assumption often made is that the overwhelming concentration of other amino acids may prevent cysteine coordination and, as a result, stabilize the Cu11 state. Recent studies show that this assumption is totally unjustified48 and so the dilemma still has to be resolved. 

HG procedures are often advocated as a means of elimination of interferences due to Cl-. However, careful consideration of the gas-liquid separator design is required to minimize or eliminate transport of Cl- to the plasma [75]. The efficiency of AsH3 production is dependent on the acidity, NaBH4 concentration, and prereductant used [76]. The use of cysteine as a reductant has all but replaced traditional reductants such as KI and Kl-ascorbic acid as the hydride yield is... 

Concentrations of unconjugated XYZ1234 and Cystein (CYS)-conjugated XYZ1234 in plasma were measured pre-dose and at predetermined times up to 48 hours post-dose. 

Overall, the results of both clinical and experimental research have strengthened the validity of the GSH hypothesis of schizophrenia and justified a clinical trial with NAC. NAC is a safe, orally bioavailable donor of cysteine, the rate-limiting substrate of GSH. Given orally, NAC is quickly absorbed, and plasma peak concentration of cysteine is reached within 120 min (Borgstrom et al., 1986 Olsson et al., 1988 Borgstrom... 

Eck HP, Gmunder H, Hartmann M, Petzoldt D, Daniel V, et al. 1989. Low concentrations of acid-soluble thiol (cysteine) in the blood plasma of HIV-1-infected patients. Biol Chem Hoppe Seyler 370 101-108. 

The distribution in body fluids of the different cystatins is remarkably different (Fig. 3). For example, while cystatin C is present in appreciable amounts in all investigated body fluids, cystatins S, SN, and SA are virtually confined to saliva, tears, and seminal plasma (Al). Cystatin D is present only in saliva and tear fluid (Al, F3). In some body compartments, e.g., spinal fluid, cystatin C represents more than 90% of the total molar concentration of cysteine protease... 

In neutral and slightly alkaline media, MPO-compound I can react directly with iodides, bromides, chlorides (K16), thiocyanates, Al-acetylmethionine, cysteine, pyridine nucleotides (S20), and phenols (K16), including tyrosine (H14) and thyroid hormones. Some of these reactions have certain biological importance. In extensive studies, Klebanoff el al. investigated the potential function of MPO as an iodide-oxidizing enzyme (K16). It was found that iodide is rapidly oxidized, forming a bactericidal derivative which produces a fall in the number of viable Escherichia coli 10 times more effectively than bromide and 100 times more effectively than chloride, if used as MPO substrates. Extremely low concentrations of iodides and bromides in leukocytes and blood plasma, however, seem to limit the importance of iodide oxidation in bacteria killing mechanisms. 

Harada, D. et al. Determination of reduced, protein-unbound, and total concentrations of N-acetyl-L-cysteine and L-cysteine in rat plasma by post-column ligand substitution high performance liquid chromatography. Anal. Biochem. 2001, 290, 251-259. 

Biotinidase is also the major plasma binding protein for biotin. The pH optimum of the enzyme is 4.5 to 5.5, and its is in the micromolar range, compared with the nanomolar concentrations of biocytin, so it will have little enzymic activity in plasma. Rather, it functions as a transport protein for biotin, preventing its urinary excretion children with biotinidase deficiency (Section 11.2.3.1) excrete large amounts of both biocytin and free biotin. Biotin is covalently bound to biotinidase in plasma, as a thioester to a cysteine residue in the active site of the enzyme (see Figure 11.1). This thioester is formed only from biocytin, not free biotin, and is presumably the (normally transient)... 

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