Proteins examples

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

The disorders listed are discussed further in other chapters. The table lists examples of mutations affecting receptors, a transporter, an ion channel, an enzyme, and a structural protein. Examples of altered or defective glycosylation of glycoproteins are also presented. Most of the conditions listed affect the plasma membrane. 

Iron-Sulfur Proteins (Examples FeS4 - and Fe4S4 - Centers)... 

The combination of this top-down proteomics approach, which generates information on the structure of the intact protein, with a bottom-up approach for protein identification (using MS/MS data of tryptic peptides from the collected fractions) has been particularly useful for identifying posttranslational modifications, cotransla-tional processing, and proteolytic modifications in a number of proteins. Examples from our work will be shown to illustrate this hybrid methodology for proteomics analysis. 

There are 20 amino acids found in the human body that are involved in protein synthesis. Refer to your textbook for a table of the 20 amino acids. The sequence of the amino acids dictates the properties of a protein. Examples of proteins include keratin in hair, hemoglobin, insulin, antibodies, and enzymes. 

Structural models, which are synthesized to imitate features of the proposed structure of the active site. These may be used to demonstrate the chemical conditions, which allow such structures to exist, to investigate their chemical properties and to give a better understanding of the spectroscopic characteristics of the native proteins. Examples of these include the mixed carbonyl/cyano complexes of iron, used to verify the infrared spectra to the hydrogenases (Fig 7.4) (Lai et al. 1998) and the nickel-thiolate complexes which have low redox potentials like the hydrogenases (Franolic et al. 1992). 

Many proteins will not yield crystals in initial crystal trials. Unfortunately, crystallization is still a trial-and-error procedure, with no real way of predicting success or failure. If you fail to get crystals in your initial trials, it need not be the end of your structural studies (although it could be ). Many of the targets for neuroscientists are going to be membrane-bound or membrane-spanning proteins, and these are notoriously difficult to crystallize. Techniques are continuously being developed and refined to improve our ability to crystallize difficult protein examples. 

TTie TOCSY 2D NMR experiment correlates all protons of a spin system, not just those directly connected via three chemical bonds. For the protein example, the alpha proton, Ft , and all the other protons are able to transfer magnetization to the beta, gamma, delta, and epsilon protons if they are connected by a continuous chain—that is, the continuous chain of protons in the side chains of the individual amino acids making up the protein. The COSY and TOCSY experiments are used to build so-called spin systems—that is, a list of resonances of the chemical shift of the peptide main chain proton, the alpha proton(s), and all other protons from each aa side chain. Which chemical shifts correspond to which nuclei in the spin system is determined by the conventional correlation spectroscopy connectivities and the fact that different types of protons have characteristic chemical shifts. To connect the different spin systems in a sequential order, the nuclear Overhauser effect spectroscopy... 

A useful concept for the classification of metal-containing proteins has been suggested by Vallee The proteins are divided into two groups metalloproteins and metal-protein complexes, on the basis of their stability during the isolation procedures. Metalloproteins retain their metal constituent during fractionation and there is a stoichiometric relationship between the metal and protein. On the other hand, the metal is loosely bound and easily lost during dialysis in metal-proteins. Examples of both types of proteins can be found in an article by Vallee and Coleman... 

Most transcription activators bind to DNA as a dimer or higher multimer (see 2.4). The dimerization relies on structural motifs which commonly occur in many different proteins. Examples for dimerization motifs are the helix-loop-hdix motif and the leucine zipper. The dimerization motifs permit the formation of DNA-boimd homodimers or heterodimers, depending upon whether the same or different proteins interact with each other (Fig. 1.38). The different dimers have different requirements for the... 

Fig. 1.41. The influence of the nucleosomes on the positioning of DNA-binding proteins. Example of a control region in which two regulatory DNA elements are separated by 60-90 bp but are brought near each other in 3D space via nucleosome formation. The super-helical arrangement of the DNA in the nucleosome brings the the two DNA elements close together. The DNA element-bound proteins PI and P2 are brought into closer contact with each other in this configuration than in a linear arrangement.

Of particular interest for regulatory processes are mechanisms by which the activity of growth regulating proteins and central transcription factors are controlled via ubiquiti-nylation. Often the cell uses signal pathway mediated protein phosphorylation in order to induce the regulated degradation of a signal protein. Examples are the G1 cychns, the tumor suppressor p53 and the inhibitor IxB. 

Fig. 3.13. Lipid anchors and basic regions as elements of the membrane association of proteins. Examples for proteins which exhibit basic residues near a lipid anchor, a) Src kinase (see ch. 8) possess a myristoyl anchor at the N-terminus as well as a stretch of basic residues, b) In Ki-Ras proteins (see ch. 9) there is a farnesyl residue at the C-terminus that serves as a lipid anchor, as weU as a stretch of Lys residues. Negatively charged head groups of phospholipids are shown as filled circles. X any amino acid.

Testing the degree of purity obtained during purification of a protein. Examples are shown in Fig. 1. 

PTOMAINE. A group of highly toxic substances (derivatives of ethers of polyhydric alcohols) resulting from the putrefaction or metabolic decomposition of animal proteins. Examples that have been isolated and prepared synthetically are cadavenne (1,5-diaminopentane), muscarine (hydrox-yethyltrimethylammonium hydroxide), putrescine (telraethylenediamine), and neurine (trimethylvinyl-ammomum hydroxide). 

The main general routes for the synthesis of the a-amino acids are illustrated in the following sections (pp. 746-750). Some of the natural amino acids can be isolated from the hydrolsates of suitable proteins examples are provided on p. 750. They are optically active having the l [(S)] configuration. The synthetic products, formed by routes not involving asymmetric syntheses, are of of course racemic, from which the optically active forms may be obtained by the process of resolution. Some resolution procedures are discussed in Section 5.19. 

There are basically three types of cytochrome P450 inducers (1) phenobarbital-like (the major class) (2) methylcholanthrene-like (which actually increases a P448 isozyme) and (3) anabolic steroids. The former two have been the most frequently studied. Research over the past 40-50 years indicates that their mechanism of action involves genetic interaction, possibly via derepression of a repressor gene, and the subsequent synthesis of mRNA for the specific enzyme proteins. Examples of phenobarbital-like enzyme inducers, the most common, are shown in Table 3.6. 

Proteins that provide all the essential amino acids in about the right proportions for human nutrition are called complete proteins. Examples of complete proteins are those in meat, fish, milk, and eggs. About 50 g of complete protein per day is adequate for adult humans. 

---