Peptides composition

Meat flavour. Meat flavour represents a large number of compounds formed during heating of the product. The flavour development mainly depends on constituents in the fresh meat, for example, fat composition, peptides, glycogen concentration, vitamin content and the heat treatment of the product. Increasing temperatures increase flavour development. According to Andersen (2000), the intensity of pork flavour has decreased during recent years, most probably as a result of the production of pork with a minimal content of intramuscular fat. 

For the orientation-based structure analysis of MAPs, uniformly oriented lipid bilayers are typically prepared on solid supports as illustrated in Fig. 2 [23, 47, 55]. These mechanically oriented membranes are advantageous for static ssNMR experiments, as they provide a robust way to orient a sample with any desired lipid composition, peptide concentration, and at any desired temperature. The lipids... 

Figure 10 Number of possible amino acid compositions (peptide combinations) as a function of the peptide monoisotopic molecular mass for [M] = 1000 Da ([M] is the nominal molecular mass, i.e., lower integer mass value). The histogram is built with a 10-mDa step. The top density of the distribution is 230 peptide compositions per mDa or per ppm. (Reprinted from Ref. 100.)...

Isoelectric point Specific activity Amino acid composition Peptide mapping... 

Figure 6.4 XRCC4 composite peptide sequence map, arranged according to domain type [36], Peptides obtained using pepsin digestion at four different enzyme-to-substrate ratios (65 1 to 520 1, upper bars) and using nepenthesin digestion at four different enzyme-to-substrate ratios (0.0075 1 to 0.38 1, lower bars). This research was originally published in Ref [36]. the American Society for Biochemistry and Molecular Biology. (See insert for color representation of the figure.)...

An apoenzyme is a polypeptide whose composition, peptide sequence and structure depend on the biological source of (he metalloenzyme. Typically, the molar mass of the polypeptide is in the range of 1.5-5x10 daltons. The polypeptide is folded into coils and sheets whose shape is determined by electrostatics and hydrogen bonding. 

Besides such textual databases that provide bibhographic information, sequence databases have attained an even more important role in biochemistry. Sequence databases are composed of amino add sequences of peptides or proteins as well as nudeotide sequences of nudeic acids. The 20 amino adds are mostly represented by a three-letter code or by one letter according to the biochemical conventions) the four nudeic adds are defined by a one-letter code. Thus the composition of a biochemical compound is searchable by text retrieval methods. 

Cleave the peptide into smaller fragments separate these fragments and determine the ammo acid composition of the fragments... 

The techniques described thus far cope well with samples up to 10 kDa. Molecular mass determinations on peptides can be used to identify modifications occurring after the protein has been assembled according to its DNA code (post-translation), to map a protein structure, or simply to confirm the composition of a peptide. For samples with molecular masses in excess of 10 kDa, the sensitivity of FAB is quite low, and such analyses are far from routine. Two new developments have extended the scope of mass spectrometry even further to the analysis of peptides and proteins of high mass. 

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

FIGURE 5.5 (a) The hydroxy amino acids serine and threonine are slowly destroyed during the course of protein hydrolysis for amino acid composition analysis. Extrapolation of the data back to time zero allows an accurate estimation of the amonnt of these amino acids originally present in the protein sample, (b) Peptide bonds involving hydrophobic amino acid residues snch as valine and isolencine resist hydrolysis by HCl. With time, these amino acids are released and their free concentrations approach a limiting value that can be approximated with reliability. 

Implicit in the presumption of folding pathways is the existence of intermediate, partially folded conformational states. The notion of intermediate states on the pathway to a tertiary structure raises the possibility that segments of a protein might independently adopt local and well-defined secondary structures (a-helices and /3-sheets). The tendency of a peptide segment to prefer a particular secondary structure depends in turn on its amino acid composition and sequence. 

For most free amino acids and small peptides, a mixture of alcohol with water is a typical mobile phase composition in the reversed-phase mode for glycopeptide CSPs. For some bifunctional amino acids and most other compounds, however, aqueous buffer is usually necessary to enhance resolution. The types of buffers dictate the retention, efficiency and - to a lesser effect - selectivity of analytes. Tri-ethylammonium acetate and ammonium nitrate are the most effective buffer systems, while sodium citrate is also effective for the separation of profens on vancomycin CSP, and ammonium acetate is the most appropriate for LC/MS applications. 

When extracting sequence information from mass spectra, not only is the m/z value at which the ions occur of importance since these provide an indication of the amino acid composition of the peptide giving rise to the ion, but so is the mass difference between adjacent ions. This indicates the particular amino acid residue that has been lost and thus provides the sequence information required. The mass differences arising from each of the amino acids are shown in Table 5.6. 

---