Cysteine , alkaline

The deterruination of amino acids in proteins requires pretreatment by either acid or alkaline hydrolysis. However, L-tryptophan is decomposed by acid, and the racemi2ation of several amino acids takes place during alkaline hydrolysis. Moreover, it is very difficult to confirm the presence of cysteine in either case. The use of methanesulfonic acid (18) and mercaptoethanesulfonic acid (19) as the protein hydroly2ing reagent to prevent decomposition of L-tryptophan and L-cysteine is recommended. En2ymatic hydrolysis of proteins has been studied (20). 

The use of CA inhibitors as diuretics is limited by their propensity to cause metabolic acidosis and hypokalemia. Their use can be indicated in patients with metabolic alkalosis and secondary hyperaldosteronism resulting for example from aggressive use of loop diuretics. Furthermore, CA inhibitors are effective dtugs to produce a relatively alkaline urine for the treatment of cysteine and uric acid stones as well as for the accelerated excretion of salicylates. Perhaps the most common use of CA inhibitors is in the treatment of glaucoma. 

Chernyak, A. S. and Shestopalova, L.F. (1976) Study of complexes of gold(I) with cysteine in an alkaline medium. Russian Journal of Inorganic Chemistry, English Translation, 21, 464—465. 

Thus the alkaline protease obtained from Bacillus licheniformis with a molecular mass of about 27 000 consists of 274 amino acid residues and has serine and histidine as active sites. Pancreatic trypsin with a molecular mass of about 24 000 contains 230 amino acid residues and also has serine and histidine as active sites. Papain (molecular mass about 23 000 and 211 amino acid residues) has cysteine and histidine as active sites. 

Thus, iodoacetamide has the highest reactivity toward cysteine sulfhydryl residues and may be directed specifically for —SH blocking. If iodoacetamide is present in limiting quantities (relative to the number of sulfhydryl groups present) and at slightly alkaline pH, cysteine modification will be the exclusive reaction. For additional information on a-haloacetate reactivities and a protocol for blocking, see Section 4.2 (this chapter). 

Iodoacetate derivatives have been used for decades to block or crosslink sulfhydryl groups in proteins and other molecules (Chapter 1, Section 5.2). At mildly alkaline pH values (pH 8-8.5), iodoacetyl derivatives are almost entirely selective toward the cysteine —SH groups in proteins. Disulfide reduction or thiolation reagents can be used to create the required sulfhydryl groups on proteins containing no free sulfhydryls. 

Alkaline phosphatases [AP, orthophosphoric-monoester phosphorylase (alkaline optimum) EC 3.1.3.1] represent a large family of almost ubiquitous isoenzymes found in organisms from bacteria to animals. In mammals, there are two forms of AP, one form present in a variety of tissues and another form found only in the intestines. They share common attributes in that the phosphatase activity is optimal at pH 8-10, is activated by the presence of divalent cations, and is inhibited by cysteine, cyanides, arsenate, various metal chelators, and phosphate ions. Most conjugates created with AP utilize the form isolated from calf intestine. 

Fig. 3. Decay of the H202 concentration versus time during the anaerobic oxidation reaction with cysteine in the presence of CuS04. First stage of constant rate (first-order in [Cu]) during the period of oxidation, second stage of increasing rate after completion of the oxidation of cysteine to cystine. Reprinted from Journal of Molecular catalysis, vol. 11, Zwart, J. van Wolput, J. H. M. C. van der Cammen, J. C. J. M. Koningsberger, D. C. Accumulation and Reactions of H202 During the Copper Ion Catalyzed Autoxidation of Cysteine in Alkaline Medium, p. 69, Copyright (2002), with permission from Elsevier Science.

Inhibits serine proteases such as trypsin and chymotrypsin. Also inhibits cysteine proteases (reversible by reduced thiols) and mammalian acetylcholinesterase Inhibits ATPase, alkaline phosphatase and tyrosine phosphatase Reagent for maintaining -SH groups in the reduced state. Effective for reducing protein disulfide bonds prior to SDS-PAGE... 

Sullivan reaction org chem The formation of a red-brown color when cysteine is reacted with l,2-naphthoquinone-4-sodium sulfate in a highly alkaline reducing medium. sal-a-van re,ak-shan ) eulpho-See sulfo-. sal-fo )... 

Protons are mainly derived from two sources—free acids in the diet and sulfur-containing amino acids. Acids taken up with food— e.g., citric acid, ascorbic acid, and phosphoric acid—already release protons in the alkaline pH of the intestinal tract. More important for proton balance, however, are the amino acids methionine and cysteine, which arise from protein degradation in the cells. Their S atoms are oxidized in the liver to form sulfuric acid, which supplies protons by dissociation into sulfate. 

Alkaline hydrolysis (with NaOH, KOH or more seldom with Ba(OH)2) is almost exclusively applied for the determination of tryptophan and phosphoamino acids. Serine, threonine, arginine, and cysteine are completely destroyed by alkaline hydrolysis, while other amino acids are racemized [190]. Since racemization also occurs during acid hydrolysis, when it is important to... 

Since thiolates are far more reactive than thiols (pK 8-9.5) in nucleophilic attack on coordinated NO, these rates are pH dependent [53]. The reaction of alkaline solutions of mercaptans with nitroprusside to yield reddish-purple solutions has long been used as a test for cysteine, glutathione or other thiol-containing compounds. However, if the solution is too basic, the nitroprusside/ hydroxide reaction becomes competitive [3]. 

The general strategy is based on selective deprotection and oxidation of pairwise cysteine residues, as specified by the orthogonal protection scheme selected for this purpose. Since multiple disulfide bonds are formed step-by-step, reaction conditions are required that prevent breaking or scrambling of the disulfide bonds already formed. Therefore, throughout the synthesis, exposure to thiols or alkaline conditions as well as lengthy reaction times that may cause disulfide disproportionation must be avoided. 

Cys(StBu) with phosphines only a slight excess of tributylphosphine is required for this purpose. Under these conditions reduction of the diselenide does not occur at all, and subsequent air oxidation of the two cysteine residues at high dilution leads in a highly selective manner to the diselenide- and disulfide-bridged peptides. The selectivity of the disulfide bridging is assured by the complete absence of thiol/diselenide exchange reactions even at alkaline pH values due to the very low reactivity of the diselenide toward mono-thiols as a result of their highly differentiated redox potentials. ... 

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