Heptapeptide

In contrast, the lower peptide (B) might be considered to be the following heptapeptide, or of similar composition. 

Potential ionic interactions may also be provided by the free amine groups of the arginine fragment. As a consequence, the net character of the heptapeptide will be polar, and the peptide would be classed as hydrophilic or lyophilic in nature. 

What is the amino acid sequence of this heptapeptide ... 

Amino acid analysis of another heptapeptide gave Asp Gin Leu Lys Met Tyr Trp NH4 ... 

Compare the electrostatic potential map for heptapeptide glyglyglyhis glyglygly to that of imidazole. Would you expect the imidazole ring in this molecule to be more or less basic than free imidazole Explain. 

Strongly hepatotoxic cyclic heptapeptides produced by some species of freshwater cyanobacteria (blue-green algae) (28). These microcystins represent a health risk to humans through drinking water, since they have been found to act as tumor promoters (29). Several chromatographic analytical procedures for microcystins have been... 

The finding that substantial 2.5-helicity may be retained in water upon the introduction of a limited number of acyclic or y9 -amino acid residues at chosen positions in the sequence, further expand the side-chain array available for functionalization of the 2.5-helical scaffold. In water, y9-heptapeptides 107 and 108 which contain two -amino acid residues [184a] and two y9 -amino acids [184b], respectively, still display a CD spectrum and NOE coimectivities characteristic of the 2.5-helix. However, the addition of a third acycHc amino acid is detrimental to the formation of the 2.5-helix in water. 

A. flos-aquae Strain S-23-g-l (Canada, Saskatchewan) Microcystins Heptapeptides MW 994 50... 

Af. aeruginosa Strain WR-70 (=UV-010) (South Africa, Transvaal) Cyanoginosins Heptapeptides MW 909-1044 50... 

Waterbloom, Australia, New South Wales) Cyanoginosin Heptapeptide MW 1035 50... 

Af. aeruginosa Strain M-228 (Japan, Tokyo) Microcystin Heptapeptide MW 994 MW 1044 50... 

Figure 8. Left The cyclic heptapeptide hepatotoxin microcystin-LA (cyanoginosin-LA) produced by the colonial cyanobacterium Microcystis aeruginosa strain WR-70 (UV-010). MW = 909. Right The cyclic heptapeptide hepatotoxin microcystin-LR (cyanoginosin-LR) produced by a waterbloom of the colonial cyanobacterium Microcystis aeruginosa collected in Lake Akersvatn, Norway, 1984-85 MW=994, 69J1).

Nodularia spwnigena has also been shown to produce a peptide with hepato-toxic activity. The more recent reports come from Australia (76), the German Democratic Republic (77), Denmark (78), Sweden (79), and Finland (80,81). Recently structure information on Nodularia toxin has been presented by Rinehart (97) for waterbloom material collected in Lake Forsythe, New Zealand, in 1984 by Eriksson et al. (81) from waterbloom material collected in the Baltic Sea in 1986, and Runnegar et al. (82) for a field isolate from the Peel Inlet, Perth, Australia. Structure work by Rinehart, Eriksson, and Runnegar all indicate that the peptide is smaller than the heptapeptide toxins. Rinehart s work (97) indicates the toxin is a pentapeptide with a similar structure to the heptapeptides and containing fi-methylaspartic acid, glutamic acid, arginine, dehydrobutyrine, and ADDA (MW 824). 

The discrete protonation states methods have been tested in pKa calculations for several small molecules and peptides, including succinic acid [4, 25], acetic acid [93], a heptapeptide derived from ovomucoid third domain [27], and decalysine [61], However, these methods have sofar been tested on only one protein, the hen egg lysozyme [16, 61, 71], While the method using explicit solvent for both MD and MC sampling did not give quantitative agreement with experiment due to convergence difficulty [16], the results using a GB model [71] and the mixed PB/explicit... 

Dlugosz M, Antosiewicz JM, Robertson AD (2004) Constant-pH molecular dynamics study of protonation-structure relationship in a heptapeptide derived from ovomucoid third domain. Phys RevE 69 021915. 

These low-temperature amide V IR and VCD isotope-edited results could be modeled with near-quantitative accuracy with DFT parameters by transferring ab initio FF, APT, and AAT parameters from computations for an a -helical heptapeptide model compound onto an o -helical 20-mer oligopeptide (Fig. 8 left). This simulation does not agree with data for the C-terminally labeled oligomer, because experimentally that end of... 

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