Cysteine isoelectric point

The isotope-coded affinity tag approach utilizes chemical labeling that allows quantitation when combined with mass spectrometry. ICAT is desirable because the chemical labeling takes advantage of the mass defects of monoisotopic stable isotopes. ICAT uses an ICAT reagent to differentially label protein samples on their cysteine residues. ICAT is advantageous because it permits the evaluation of low-abundance proteins and proteins at both extremes of molecular weights and isoelectric points.60... 

In dyeing the hair and the suede portion a number of factors must be allowed for. The keratin of the hair contains basically the same amino acids as the collagen of the skin but in a different ratio. The keratin of the hair includes cysteine, which cross-links the polypeptide chain and imparts stability. The collagen of the skin does not have these substances, and the cross-links are made by the tanning agent. On the other hand, only L-hydroxyproline can be found in the collagen. As a result the thermal stability is different, and in addition the isoelectric points of the two polypeptides diverge. 

The purification and partial characterization of a novel trypsin-like cysteine protease, Pr4 from M. anisopliae was reported by Cole et al. (1993). The enzyme, with an isoelectric point of 4.6 and a molecular mass of 26.7 kDa, exhibited trypsin-like specificity, but according to... 

Find the isoelectric point and the concentrations of all ionic species from 1.0 M cysteine solution at pH = 7.00. 

Thiol methyltransferase has been detected in erythrocytes, lymphocytes, lungs, cecal, and colonic mucosae. The nature and number of thiol methyltransferases is not clear at the present time. A cytosolic enzyme and a microsomal enzyme have been reported, with the microsomal enzyme being dissociated from membrane relatively easily. The microsomal enzyme in rat liver has been purified to homogeneity. The enzyme is a 28,000-dalton monomer with an isoelectric point of 6.2. A wide variety of xenobiotic thiols are methylated, but cysteine and glutathione are not substrates. S-Methylation is an important component in the thiomethyl shunt. Thiomethyl conjugates are metabolized to the methylsulfoxides by oxidation (see Chapter 10) and reenter the mercapturic acid pathway as substrates for glutathione S-transferase. 

Determine the charge on this amino acid as a function of pH. How does your result compare with the reported isoelectric point (pi) for cysteine of 5.68 ... 

The gene encodes for a secreted protein, with the mature protein possessing 119 amino acids. The calculated molecular mass and isoelectric point of the recombinant form are very similar to those obtained by electrophoretic methods on the purified protein (Barde et al., 1982). A striking feature of the primary structure of mature BDNF is its similarity to NGF. There are 51 amino acids common to the various NGF s and to BDNF, including all six cysteine residues (Leibrock et al.,... 

A SAM of L-cysteine on a gold-coated cantilever was demonstrated to be selective for Cu(II) in a pH 5 phosphate buffer. The SAM forms upon immersion of the gold-coated cantilever in a 10 M solution of L-cysteine witii tile pH adjusted to the isoelectric point, pH 5, using a 10 M phosphate buffer for 12 hrs. This was followed by rinsing three times with the pH 5 phosphate buffer. The surface structure, shown in Figure 8, is thought to involve a Cu(II) bound by two L-cysteine molecules, each L-cysteine having bidentate coordination to the Cu(II). 

The anticq>ated sur ce structure of the L-cysteine SAM on gold and its conq>lex witii Cu is shown in Figure 8. Electrochemical and XPS data suggest one Cu per two cysteine ligands (23). Literature reports indicate that the best complexation performance for tiie electrochemical sensors was at pH = S, the isoelectric point of L-cysteine. Similar optimal performance at pH = S was also observed for microcan ever deflection experiments. The deflection anq>litude caused by Cu complexation with the L-cysteine monolayer was much less for experiments performed at pH = 3 or pH = 7, than at pH = 5. 

The isoelectric point of histidine is 7.64. At this pH, histidine has a net charge of zero and does not move from the origin. The pi of cysteine is 5.02 at pH 7.64 (more basic than its isoelectric point), cysteine has a net negative charge and moves toward the positive electrode. The pi of lysine is 9.74 at pH 7.64 (more acidic than its isoelectric point), lysine has a net positive charge and moves toward the negative electrode. 

The a-amylase (mol. wt. 5.0 x 10 pi 9.2) from a thermophilic bacterium (found in a hot spring in Japan) is more thermostable than a-amylases from mesophilic sources. It contains two cysteine residues, but no disulphide linkages, and 20% of a-helix. The effects of pH, metal ions, and denaturing agents on the thermal stability of the enzyme were examined. It is most stable at its isoelectric point and is stabilized by calcium ions one of the bound Ca ions could not be removed by electrodialysis unless the enzyme was first denatured. 

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