Proteins alternative secondary

The secondary structure of a protein is the shape adopted by the polypeptide chain—in particular, how it coils or forms sheets. The order of the amino acids in the chain controls the secondary structure, because their intermolecular forces hold the chains together. The most common secondary structure in animal proteins is the a helix, a helical conformation of a polypeptide chain held in place by hydrogen bonds between residues (Fig. 19.19). One alternative secondary structure is the P sheet, which is characteristic of the protein that we know as silk. In silk, protein... 

Although flavonoids are found in many cellular compartments, it is only the mechanisms for vacuolar import that have been characterized in any detail. Alternative import mechanisms have been found that involve direct uptake, carrier proteins, or secondary modifications triggering importation. While commonalities are found for the import of anthocyanins, flavones, flavonols, and PAs, differences have also been observed for the different types of flavonoid. 

Because symmetry is a recurring theme for protein-DNA interactions, the DNA sequence may have functional importance. One possibility is that the DNA sequence could be a binding site for a dimeric regulatory protein. Alternatively, inverted repeat sequences sometimes serve as hot spots for genetic rearrangements because they may form hairpin secondary structures that block DNA polymerases or are processed by structure-specific endonucleases. 

If the allelochemical is hydrophylic, it cannot enter into the cell and act from outside by binding with chemoreceptors. The compounds from allelopathically active plants may serve as chemosignals and their signalling occurs via alternative pathways (i) Chemoreceptor (sensors) — transducers (G-proteins) —> secondary messengers (Ca2+, cyclic AMP or GMP, inositol triphospate, etc) —> organelles or (ii) Chemoreceptor (sensors) —> ion channels —> action potential organelles, or (iii) Chemoreceptor (sensors) —> ion channels —> cytoskeleton— organelles (Roshchina, 2005 a). What is the effect of acted allelochemical on the pathways, could be analysed to study the effects of substances on separate sites of the transduction chain. 

Although most assays perform well with regard to specificity and reproducibility, the major problem remains their standardization (A9, Dl, K30, L4). There is currently no internationally accepted standard, and the selection of a reference material raised many problems (A8, G5, K30, L4). A number of questions have not been solved Should the standard consist of several apo(a) isoforms Can the reference material be lyophilized Should results be expressed as mass or as moles of apoprotein or lipoprotein How should the protein mass of the primary standard be determined What are optimal storage conditions for the secondary standard Which method can be used as a reference method Can recombinant apo(a) represent an alternative for a primary standard These problems came to light in the course of the international surveys whose results were presented at the Lp(a) Workshop in New Orleans (1992) (L4). 

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