Octapeptides

Substitution of Trp by D-Trp increased the potency of somatostatin (101). Most other substitutions, however, are deleterious to biological activity. Cychc octapeptide analogues of somatostatin retain high potency one of them, CTOP, is a potent mu-opioid antagonist. 

CCK has been detected in two principal forms, ie, the traditional 33-amino acid peptide, and an octapeptide CCK-8. The intestine produces mainly CCK-33 (133) and the brain produces mainly CCK-8 (132). The CCK precursor contains one copy of CCK-33 (133,134) this peptide is flanked on both ends with double basic residues, whereas CCK-8 is formed from CCK-33 by cleavage of a single basic residue. 

Analysis of the blood of a catatonic football fan revealed large concentrations of a psychotoxic octapeptide. Amino acid analysis of this octapeptide gave the following results ... 

The following facts were observed a. Partial acid hydrolysis of the octapeptide yielded a dipeptide of the structure... 

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

Amino acid analysis of an octapeptide revealed the following composition ... 

What is an amino acid sequence of the octapeptide Four sequences are possible, but only one suits the authors. Why ... 

B) A solution of (SM) (330 mg) in trifluoroacetic acid (7 ml) was kept under nitrogen at room temperature for 15 minutes. Ether (100 ml) was added and the precipitate was filtered, washed thoroughly with ether and dried. This material (300 mg) was added in portions to concentrated sulfuric acid (18 ml) cooled at -20°C with vigorous stirring. After 15 minutes a solution of potassium bisulfate in concentrated sulfuric acid (408 mg in 3 ml) was added. The reaction mixture was stirred for 75 minutes at -15°Cand then stored at -7°Cfor 285 minutes. The sulfuric acid solution was poured into cold ether (400 ml) precipitate was filtered, washed with cold ether, and suspended in cold water. Complete solution was then achieved by careful addition of 2N sodium hydroxide. Acidification with N hydrochloric acid led to the precipitation of the desired octapeptide sulfate ester. Yield 200 mg. 

The octapeptide angiotensin 11 has the sequence Asp-Arg-VaJ-Tyr-Ile-His-Pro-Phe. What fragments would result if angiotensin I [ were cleaved with trypsin With chymotrypsin ... 

Rousseau, R., Schreiner, E., Kohbneyer, A., and Marx, D., Ternperamre-dependent conformational transitions and hydrogen-bond d3mamics of the elastin-bke octapeptide GVG(VPGVG) A molecular-dynamics study, Biophys. J., 86, 1393-1407, 2004. 

Fig. 2.20 The / -peptide 2.5]2-helical structure [119, 160]. (A) Stereo-view along the helix axis of the left-handed 2.5,2-helix formed by / -octapeptide 101 consisting of (R,R)-trans-2-...

Ductal carcinoma octapeptide 0.014 BPTI (580 atoms) 0.070 Lysozyme (1264 atoms) 0.162 Carboxy-myoglobin (1532 atoms) 0.174 Hemoglobin (5478 atoms) 0.518... 

Methods. In using molecular dynamics for conformational analysis, there are many possible approaches. Assume that one is able to dedicate a machine for two weeks for this task. For this octapeptide, 70 energy evaluations can be performed each second. This implies that in two weeks, roughly 100 million iterations can be performed. Three distinct approaches could be ... 

Figure 6. A stereo representation of the "best" minimized structure from the 300K octapeptide simulations.

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