Quaternary system definition

Strictly speaking an intermetallic compound is a compound formed by two metals, such as NiaAl, AI2C, etc., although the definition has been broadened to include metal-metalloid (Si, Ge, and As) and even nonmetals (FeaC). There are over 11,000 known intermetallic compounds, discovered primarily from their phase diagrams. It is estimated that there could be as many as 500,000 possible ternary systems and 10 quaternary systems with only a small fraction actually known (see Villars, 1994). Intermetallic compounds possess... 

Figure 5 Vertical model grid and definition of model parameters. Reproduced from Schlitzer R, Usbeck R, and Fiscjer H (2004) Inverse modeling of particulate organic carbon fluxes in the South Atlantic. In Wefer G, Mulitza S, and Ratmeyer V (eds.) The South Atlantic in the Late Quaternary - Reconstruction of Material Budget and Current Systems, pp. 1-19. Berlin Springer, with permission of Springer Science Business Media.

According to the definition, proteolytic reaction requires the presence of aqueous phase. Because substrate proteins always contain peptide bonds sensitive to a protease, theoretically the proteolytic reaction will occur in any system containing proteins and protease(s) in solution. However, because proteins have a three-dimensional structure, those sensitive peptide bonds buried inside a compact tertiary structure cannot be hydrolyzed. Even some peptide bonds on the surface of a tertiary-structured protein may become buried if the protein associates with other proteins to form quaternary structures (either mono- or heteroassociates). Therefore, some proteins are highly resistant to certain proteases, although they contain peptide bonds sensitive to the enzyme. The resistance of native proteins to certain kinds of proteolysis is essential for them to carry out biological functions. 

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