Molecular weights of proteins

The polarity and thermal instability of biopolymers, together with the almost exclusive formation of singly charged ions renders APCl an inappropriate ionization technique for their study. Much of the early work involving electrospray ionization, on the other hand, was connected with the analysis of this type of molecule, in particular determining the molecular weight of proteins for which it is particularly effective. 

MALDI-ToF is a technique that allows the molecular weights of proteins and peptides to be determined. It is less susceptible to suppression effects than electrospray ionization and thus is able to be used for the direct analysis of mixtures. In the case of a crude tryptic digest, MALDI-ToF will provide a molecular weight profile of the polypeptides present without the analysis time being extended by the need to use some form of chromatographic separation. 

Hedrick, JL Smith, AJ, Size and Charge Isomer Separation and Estimation of Molecular Weights of Proteins by Disc Gel Electrophoresis, Archives of Biochemistry and Biophysics 126, 155, 1968. 

Just as gel electrophoresis methodology is commonly used to determine homogeneity, as well as molecular weights of proteins these techniques may be used similarly for dendrimer analysis. Other uses have included the assessment of DNA/dendrimer binding constants which have been studied using gel electrophoresis. Application of gel electrophoresis in dendritic science will be discussed from these three aspects. 

Andrews, P. Estimation of the molecular weight of proteins by Sephadex gel-filtration. Biochemic. Journ. 97, 222—233 (1964). 

EquUibrium ultracenttifiigation has played a crucial role in establishing the molecular weights of protein molecules on an ab initio basis [3,4], that is, without requiring calibration with macromolecules of known molecular weight. 

Immunoprecipitation followed by SDS-PAGE and immunoblotting, is routinely used in a variety of applications to determine the molecular weights of protein antigens, to study protein-protein interactions, to determine specific enzymatic activity, to monitor protein post-translational modifications and to determine the presence and quantity of proteins. The IP technique also enables the detection of rare proteins which otherwise would be difficult to detect since they can be concentrated up to... 

Because osmotic pressures can be experimentally measured down to rather low values, the Van t Hoff equation proves to be valuable for determining the molecular weights of proteins and other high polymers, as illustrated in Sidebar 7.13. Other practical aspects of osmosis, dialysis, and reverse osmosis phenomena in the physiological and industrial domain are described briefly in Sidebar 7.14. 

Gel filtration has been used to measure the molecular weights of proteins and carbohydrates,24 and it should also be applicable to polyglycoses. 

SDS-PAGE is valuable for estimating the molecular weight of protein subunits. This modification of gel electrophoresis finds its greatest use in characterizing the sizes and different types of subunits in oligomeric pro-... 

The molecular weights of proteins studied thus far range from about 5000 to 15,000. The use of three-dimensional Fourier transform NMR may ultimately permit the study of macromolecules up to a molecular weight of 40.000. 

It can be shown that the molecular weight of protein in each asymmetric unit is given by... 

A more complicated task faces an ESI-LC/MS designed to separate and determine the molecular weights of proteins. The proteins have to be separated by the column, the multiply charged ion envelope must be measured, and deconvolution calculations made to determine the molecular weights of the separated protein(s). Often, there are partially resolved proteins mixtures and the overlapping peak envelopes must be resolved to determine molecular weight for both components present. 

Table 2.1. Molecular weights of proteins and glycoproteins associated with the tegumental brush border of Hymenolepis diminuta. (Data from Knowles Oaks, 1979.) (See also Figs. 6.3 and 6.6)...

To determine molecular weights of proteins by gel electrophoresis, a protein must be rendered into the random coil conformation by breaking disulfide bonds (mercaptoethanol) and physical bonds (urea), and the charge must be made overwhelmingly negative with SDS. Electrophoresis may be performed at a neutral pH. 

Mass Spectrometry Usage of analytical devices that can determine the mass (or molecular weight) of proteins and nucleic acids, the sequence of protein molecules, the chemical organization of almost all substances and the identification of gram-negative and gram-positive microorganisms. 

For example, the respective values at pH 10.6 are 0.262, 0.494, and 1.04 mole per cent (ratio of about 1 2 4) at pH 11.2 the values are 0.420, 0.780, and 1.32 mole per cent and at pH 12.5 (pH of 1% protein solution in 0.IN NaOH), the respective values are 0.762, 0.780, and 2.62 mole per cent. (Note that the value of casein approaches that of gluten at this pH). The observed differences in lysinoalanine content of the three proteins at different pH values are not surprising since the amino acid composition, sequence, protein conformation, molecular weights of protein chains, initial formation of intra- versus intermolecular crosslinks may all influence the chemical reactivity of a particular protein with alkali. Therefore, it is not surprising to find differences in lysinoalanine content in different proteins treated under similar conditions. These observations could have practical benefits since, for example, the lower lysinoalanine content of casein compared to lactalbumin treated under the same conditions suggests that casein is preferable to lactalbumin in foods requiring alkali-treatment. 

Protein Molecular weight of protein Amount of protein (g) Amount of iron (g) % of total body iron Nature of iron heme (H) or nonheme (N) Number of iron atoms bound per molecule Valence state Function... 

The dipolar coupling with the unpaired electron is the main source of relaxation for protons and for nuclei of the metal ligands other than those coordinated to the metal ion. This dipolar coupling can be modulated by Tr (due to motion of part or whole of the molecule) or by Tj (from the change of state of the electron spin). Due to the relatively large molecular weight of protein molecules, electron relaxation is dominant and Tc = Tj. The nuclear relaxation rates are given by (Solomon, 1955)... 

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