Peptide isoelectric point

Properties and Structure. a -Acid glycoprotein (a -AGP) has a molecular mass of about 41,000 and consists of a peptide chain having 181 amino acid residues and five carbohydrate units (14,15). Two cystine disulfide cross-linkages connect residues 5 and 147 and residues 72 and 164. The carbohydrate units comprise 45% of the molecule and contain siaUc acid, hexosamine, and neutral hexoses. In phosphate buffer the isoelectric point of the... 

Thomson MOW Click Organic Interactive to learn to estimate isoelectric points for simple amino acids and peptides. 

When the log /J/pH measurement of a peptide is performed by the shake-flask or the partition chromatography method (using hydrophilic buffers to control pH), usually the shape of the curve is that of a parabola (see Ref. 371 and Fig. 1 in Ref. 282), where the maximum log I) value corresponds to the pH at the isoelectric point (near pH 5-6). Surprisingly, when the potentiometric method is used to characterize the same peptide [275], the curve produced is a step function, as indicated by the thick line in Fig. 4.5 for dipeptide Trp-Phe. 

An important quantity characterizing the amino acids, peptides and proteins is the isoelectric point, which is the value of pH at which the ampholytes do not migrate in an electrical field. This occurs when... 

Cargile, B. J., Stephenson, J.L., Jr. (2004). An alternative to tandem mass spectrometry isoelectric point and accurate mass for the identification of peptides. Anal. Chem. 76, 267-275. 

What charge would a peptide with an isoelectric point of 7.2 have at pH 8.9 ... 

It should also be noted that new sample probes can generate additions to the sample information queries asked of the user at the beginning of the "probe session." Thus, protein probes required the addition of queries regarding molecular weight, isoelectric point and whether biological activity is to be preserved in the chromatographic step. These questions are triggered only if the user specifies the sample as a peptide or protein in answer to the initial sample questions. Also, once the sample is specified as a protein, the question as to the pKa or pKb of the... 

At its isoelectric point, histidine is said to be zwitterionic, as it has both anionic and cationic properties. Most other amino acids are also zwitterionic at neutral pH. Peptides and proteins also have isoelectric points, which can vary widely depending on the composition of the amino acids. 

The pH at which an amino acid, a peptide, or a protein has zero overall charge after summing the contributions of all the charges is called the isoelectric point (pi). 

Human insulin is a small protein consisting of 51 amino acids with a molecular weight of 5734 and an isoelectric point (pi) of 5.4. Insulin is made up of two peptide chains connected by 2 disulfide bonds the A chain with 21 amino acids and the B chain with 30 amino acids. This small recombinant protein has been produced on very large scales for over two decades. The various commercial processes in production have been improved over the years but are still very complex [18-21]. 

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