Naming compounds polypeptide

As its name implies, this complex transfers a pair of electrons from NADH to coenzyme Q a small, hydrophobic, yellow compound. Another common name for this enzyme complex is NADH dehydrogenase. The complex (with an estimated mass of 850 kD) involves more than 30 polypeptide chains, one molecule of flavin mononucleotide (FMN), and as many as seven Fe-S clusters, together containing a total of 20 to 26 iron atoms (Table 21.2). By virtue of its dependence on FMN, NADH-UQ reductase is a jlavoprotein. 

For the HPLC separation of low molecular weight organic compounds and various biomacromolecules, the near-equilibrium criterion has generally been assumed for the binding and desorption behaviour. Changes in thermodynamic parameters due to polypeptide- or protein-ligate interaction can thus be depicted in terms of the Gibbs-Helmholtz relationship, namely,... 

The design of linear protein sequences that are not mere copies of natural compounds has to address the major inherent problem of polypeptide chain folding, i.e., the competition between intra- and intermolecular interactions. To overcome such uncertainties, amphiphilic polypeptides were also attached as neighboring side chains to a carrier molecule or template assembly protein (TASP), namely ACCKAPGKAKCNH. Both central (LysAlaLys = KAK) units have all NH2 groups on the same side of the ring, and one can assemble... 

These radicals can be introduced into all the simple mono-amino acids, such as alanine, leucine, tyrosine, etc. also into cystine and the dicarboxylic acids when the compounds such as dialanyl-cystine and asparagyl-dialanine are formed. They can also be introduced into the molecule of a di, tripeptide, etc., as can be seen from the appended list of polypeptides synthesised by this method, which, however, only allows of the chain of amino acids being lengthened on one side, namely, at the amino group end. 

More amino acids can react in the same way to form a tetrapeptide, a pentapeptide, and so on, until a chain of hundreds or even thousands of amino acids has formed. The compounds with shortest chains are often simply called peptides, those with longer chains are called polypeptides, and those with still longer ehains are called proteins. Chemists differ about where to draw the lines in the use of these names, but generally polypeptide chains with more than 50 amino acids are called proteins. However, the terms protein and polypeptide are often used interchangeably. 

Compounds in which amino acids are linked to each other by amide bonds, according to the principle of protein structure, were called peptides by Emil Fischer. Dipeptides contain 2, tripeptides 3, etc. and polypeptides many amino acids. The upper limit that marks the transition to proteins, remains vague. Nowadays protein chains are described as polypeptides in numerous publications. It might perhaps be reasonable to consider peptides to have a mass of 10000 daltons (lOkDa) as maximum. Some time ago B. Helferich proposed the designation oligopeptide for compounds up to the range of 10 amino acid residues, but this name has not been widely accepted. 

Much of the negative attitude about antibiotics arises because the aforementioned problems are inherent in the nature of penicillin and other common antibiotics—namely, they are xenobiotic compounds that have evolved in a context that virtually assures that for every antibiotic. Nature has co-evolved a defense, or resistance, to it. If each and every one of Nature s antibiotic substances conformed to this same general pattern, then we would indeed be in a difficult situation. Fortunately, this is not the case, and nisin is an excellent example of an antibiotic with something very different to offer. First of all, it is a peptide and, therefore, a polymer of amino acids. Peptides are not alien things, and our metabolism has evolved around utilizing polypeptides as food. An antimicrobial peptide such as nisin will be digested in a normal residue-free fashion, unlike penicillin, which persists in the gut and floods out into the tissues, where its fate is problematic. 

The water extract of Buddieja qfficinalis (Buddlejaceae) inhibited vascular inflammation and atherosclerotic disorders. Recently, Tai et al. isolated several compounds from the flowers of the plant and tested their in vitro effects on the proliferation of rat aortic vascular smooth muscle cells (VSMCs). Among the tested compounds, two iridoids, namely, methylscutelloside (146) and methylcatalpol (147), showed significant inhibitory effects on homodimer platelet-derived growth factor beta polypeptide (PDGF-BB)-induced proliferation in rat aortic VSMCs. Methylscutelloside (146) decreased cell proliferation at 10, 30, and 50 pM, with inhibition of 39.1%, 42.0%, and 79.6%, respectively, while methylcatalpol showed significant inhibition (80%) only at 50 pM concentration. Their inhibitory effect on rat aortic VSMC proliferation may be useful for the treatment of atherosclerosis [153]. 

The specificity of the various proteol rtic enzymes was established with synthetic substrates, namely peptides or substituted peptides. Only through use of these compounds was it possible to devise unambiguous experiments. Much later it became possible to check the results on proteins or polypeptides of known constitution, e.g. insulin or ribonuclease. The check actually revealed a few deviations from the rules established earlier. 

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