Protein heterogeneity

As with any analytical technique, generation of a reproducible standard curve with minimal error is critical. An assay calibration consists of several steps during which the value of the primary standard is transferred to the calibrators used in the final assay [22]. Immunoassay optimization is usually difficult due to protein heterogeneity and matrix effects and these factors, heterogeneity and matrix effects, will also affect MIP based assays [22]. 

Ipatov, V.V. and Lukyanenko, V.I. (1979). Fish serum proteins heterogeneity, structure and functions (In Russian). Uspekhi Sovremennoy Biologii 88,108-124. 

It is now recognised that a substantial number of proteins, especially enzymes, are polymorphic in that they exist in the cell as multiple molecular forms differing in certain of their physico-chemical properties. Each form of a polymorphic enzyme is called an isoenzyme or isozyme. Electrophoretic techniques provide convenient methods whereby this protein heterogeneity can be investigated and the approach has been widely exploited to characterise parasites. In short, aqueous parasite extracts are electro-phoresed, or focused isoelectrically, and separated proteins are stained generally (usually with Coomassie Blue) or more specifically with a histochemical (enzyme) stain (the zymogram technique). Further details of individual procedures and the use of the approach in parasite identification are to be found in a number of recent reviews (104,258,413,536,615,856). 

Figure 4B shows the set of 31 produetive and 21 unproductive electron transfer reactions in multi-redox center oxidoreduetases with structures available in the Protein Data Bank (PDB). Both productive and unpro-duetive reactions have statistically indistinguishable distributions, which are in turn indistinguishable from the arbitrary protein paeking distribution. Thus Nature has not generally selected protein heterogeneity to assist pro-duetive and hinder counterproductive eleetron tunneling. 

Problems Encountered in the Purification and Analysis of Chemically Modified Proteins. One of the main problems plaguing the chemical modification expert is the heterogeneities of the products. With chemically modified proteins heterogeneity may make purification nearly impossible and analysis merely a reflection of an average value for the heterogeneous population of molecules. Heterogeneity can be caused by incomplete modifications as well as by side reactions of either a physical or chemical nature. Careful considerations of these as well as other possible problems is mandatory in achieving satisfactory purifications and analyses. A recent review (10) should be consulted for a more comprehensive discussion of the purification and analysis of chemically modified proteins. 

In some cases, a broad or distorted band for a single protein may reflect different stable structures of the native (biologically active) molecule. In such cases the apparent band broadening results from partial resolution of the mixture. Two types of protein heterogeneity can be distinguished. First,... 

A second kind of protein heterogeneity can arise from the stability of different native conformers for the same compound. Strop et al (103a) have noted broad hands in HIC for human serum albumin and a-fetoprotein, and have attributed this to such an effect. 

Constant vital functions thus frequently need to have at their disposal several editions of a given type of genes in several regions of the genome that are successively activated and inactivated, or vice versa, with respect to protein-synthesizing ability. This view is advanced as an explanation of the generality of the most important types of major-component multiplicity in proteins. These types are on the one hand the successive embryonic and adult editions of a protein and on the other hand the different editions found at any one time in different tissues of the same animal. The latter type of protein heterogeneity has been referred to earlier and may be interpreted in the same terms. In each tissue the particular intracellular... 

Further problems Involved are related more to biological rather than technical parameters and, thus, differ in every system. The quality of an Iji vivo footprint mainly depends on the complexity of the genome analyzed and on the occupancy of the target site by the DNA binding protein. Heterogeneity in the cell population with regard to the function analyzed due to mixed cell types, cell cycle dependence in unsynchronized cultures or variable responsiveness to certain environmental stimuli will obscure the results. The occupancy of a factor within a cell is also influenced by its abundance and its affinity to the binding sites (on- and off-rates). 

Piccardo P, Dlouhy SR, Elevens PM, et al. Phenotypac variabUity of Gerstmaim-Straiissler-Scheinker disease is associated with prion protein heterogeneity. / Neuropathol Exp Neurol. 1998 57(10) 979-988. 

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