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A multiprotein complex (or protein complex) is a group of two or more associated polypeptide chains. The different polypeptide chains may have different functions. This is distinct from a multienzyme polypeptide, in which multiple catalytic domains are found in a single polypeptide chain. Protein complexes are a form of quaternary structure. Proteins in a protein complex are linked by non-covalent protein–protein interactions, and different protein complexes have different degrees of stability over time. These complexes are a cornerstone of many (if not most) biological processes and together they form various types of molecular machinery that perform a vast array of biological functions. Increasingly, scientists view the cell as composed of modular supramolecular complexes, each of which performs an independent, discrete biological function. Through proximity, the speed and selectivity of binding interactions between enzymatic complex and substrates can be vastly improved, leading to higher cellular efficiency. Unfortunately, many of the techniques used to break open cells and isolate proteins are inherently disruptive to such large complexes, so it is often difficult to determine the components of a complex. Examples of protein complexes include the proteasome for molecular degradation and most RNA polymerases. In stable complexes, large hydrophobic interfaces between proteins typically bury surface areas larger than 2500 square angstroms. == Function == Protein complex formation sometimes serves to activate or inhibit one or more of the complex members and in this way, protein complex formation can be similar to phosphorylation. Individual proteins can participate in the formation of a variety of different protein complexes. Different complexes perform different functions, and the same complex can perform very different functions that depend on a variety of factors. Some of these factors are: * Which cellular compartment the complex exists in when it is contained * Which stage in the cell cycle the complexes are present * The nutritional status of the cell * Others Many protein complexes are well understood, particularly in the model organism ''Saccharomyces cerevisiae'' (a strain of yeast). For this relatively simple organism, the study of protein complexes is now being performed genome wide and the elucidation of most protein complexes of the yeast is ongoing. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Multiprotein complex」の詳細全文を読む スポンサード リンク
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