Proteins, classes simple

Figure 4-21. Serum electrophoresis. Serum electrophoresis is the separation of serum proteins by simple zonal electrophoresis. It is usually carried out under slightly alkaline conditions where most of the proteins or classes of protein are negatively charged and thus migrate towards the anode.

The use of SDS is not always without drawbacks. One of the most important is encountered when the sample is rich in DNA. A terrible viscosity results, which can hamper the electrophoresis process. Moreover, some protein classes (e.g. glycoproteins) bind SDS poorly and are thus poorly separated in the subsequent electrophoresis. In such cases, it is advisable to use cationic detergents. They are usually less potent than SDS, so that a urea-detergent mixture must be used for optimal solubilization (MacFarlane 1989). Moreover, electrophoresis in the presence of cationic detergents must be carried out at a very acidic pH, which is not technically simple but still feasible (MacFarlane 1989). This technique has however gained recent popularity as a double zone electrophoresis method able to separate even membrane proteins (Hartinger et al. 1996), and showing more separation power than SDS electrophoresis alone. 

Proteins are polypeptides containing from 50 to thousands of amino acid residues, and they vary greatly in structure and composition. They can he divided into two classes simple and conjugated. Simple proteins consist only of amino acids. Two examples of simple proteins are insulin and chymotrypsin. Insulin, a hormone that is essential to controlling the concentration of glucose in the blood, has 51 amino acid residues in two linked chains (Figure 15.10). Chymotrypsin, an enzyme that aids in the digestion of proteins in our diet, contains 245 amino acid residues. 

To date, various other routes of electron dehveiy to P450s have been recognized, leading to diverse classificahons, e.g., those suggested by Hannemann et al. (Table 8.2) [35]. The diversity of the P450 systems is striking, ranging from complex systems composed of three individual proteins (classes I, HI, and IV) to the more simple catalytic self-sufficient systems that harbor the... 

The lipoproteins are macromolecules that are complexes of proteins with simple or complex lipides. Complexes of steroids and their esters and carotenoids and their esters with proteins are generally classed under this heading. 

In bacteria, accumulation of substrates against a concentration gradient can occur through two main classes of transport systems (see [30] for a summary). The prototype of the first class of transporters is the /3-galactoside permease of Escherichia coli (see [31]). It is a relatively simple system involving only a single membrane-bound protein. It catalyzes a lactose-H symport. Other transporters... 

DKPs are simple and easy to obtain and are quite common by-products of synthetic, spontaneous, and biological formation pathways. DKP formation has been well documented as side reactions of solid-phase and solution-phase peptide synthesis. In addition, DKPs have been shown to be decomposition products of various peptides, proteins, and other commercial pharmaceuticals. Cyclic dipeptides were found to be present in solutions of human growth hormone, bradykinin, histerlin, and solutions of agents within the classes of penicillins and cephalosporins. " DKPs are also enzymatically synthesized in several protists and in members of the plant kingdom. Hydrolysates of proteins and polypeptides often contain these compounds and they are commonly isolated from yeasts, lichens, and fungi. ... 

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