Molecular weight of peptides

Reversed-phase HPLC is widely utilized to generate a peptide map from digested protein, and the MS online method provides rapid identification of the molecular mass of peptides. The HPLC-MS-FAB online system is a sensitive and precise method for low-MW peptides (<3000 Da) even picomol quantities can be detected. However, as the MW of the analytes increases, the ionization of peptides becomes more difficult and decreases the sensibility of the FAB-MS (112). Electrospray ionization (ESI-MS) was found to be an efficient method for the determination of molecular masses up to 200,000 Da of labile biomolecules, with a precision of better than 0.1%. Molecular weights of peptide standards and an extensive hydrolysate of whey protein were determined by the HPLC-MS-FAB online system and supported by MALDI-TOF (112). Furthermore, HPLC-MS-FAB results were compared with those of Fast Performance Liquid Chro-motography (FPLC) analysis. Mass spectrometry coupled with multidimensional automated chromatography for peptide mapping has also been developed (9f,l 12a). 

Molecular weight of peptide chains 57,500 a-Subunit 33,000-36,000 /3-Subunit 21,000... 

Table 11.6 Diffusion coefficients and molecular weights of peptides and proteins"...

These results are sufficiently encouraging for studying mixtures of non-derivatized peptides with the following advantages normal increase of the abundance of the deprotonated molecule [M-H] which affects sensitivity directly no useless increase of the molecular weights of peptides, which had an unfavorable effect on the resolution of MIKE spectra. 

This section defines MS terms and explains good MS practices for use in determining the molecular weights of peptides and proteins. 

Table 1. Sequence and molecular weight of peptides used.

MALDI MS is an analytical approach suitable for obtaining molecular weights of peptides and proteins from complex samples. MALDI MS can profile the peptides and proteins from single-cell and small tissue samples without the need for extensive sample preparation, except for cell isolation and matrix preparation. Strategies for peptide identification and characterization of post-translational modifications are versatile and broadly applicable. " ... 

The characterization of the proteins adsorbed, or immobilized, on substrates by TOF-SIMS has contributed to the development of other analytical techniques. In 1986, the isolation of an apolipoprotein was studied with TOF-SIMS [68], and an accurate molecular weight of peptides was obtained. Moreover, it became evident at that time that it was feasible to monitor on a microscale basis for the genetic polymorphisms of proteins, and also for posttranslational modifications, by this method. 

When analyzing the molecular weight of peptides from larger proteins (>30 kDa) a gradient of up to 100 min improves peptide separation. 

Figure 18 Size exclusion chromatography pattern of a wheat protein hydrolysate (left) and percent composition of the fractions having molecular mass within the known values of standard substances (right). Molecular weights of peptides are only approximately determinable, since their hydrodynamic properties are not necessarily identical with those of the marker substances. Chromatographic conditions stationary phase TSKgel Toyopearl HW-40F (Tosoh Co., Japan) 10 X 500 mm eluant 0.1 M NaCl in 0.1 M phosphate buffer pH 7.1 flow 0.4 ml/min detection UV 220 nm. (Unpublished data.)...

Hung, C. H., Strickland, D. K., and Hudson, B. G. (1977). Estimation of molecular weights of peptides and glycopeptides by thin layer gel filtration. Anal. Biochem. 80 91-100. 

Molecular Weights of Peptides and Proteins. Traditionally, organic mass spec-troscopists have utilized peaks corresponding to monoisotopic ion species (containing only H, N, 0, etc.) to determine molecular or fragment masses (Table 10.1). While their relative abundances are low, the contribution to the molecular-ion mass from one or several and isotopes increases for peptides... 

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