Hydrophobic interactions membrane-bound enzymes

As with other multisubunit enzymes (e.g., allosteric enzymes), the structural integrity of a membrane-bound enzyme primarily is maintained by noncovalent interactions such as hydrogen bonding, electrostatics, and hydrophobic interactions. Hydrophobic polypeptides (or hydrophobic portions of polypeptides) apparently are used to anchor the enzymes to the membrane through interactions with phospholipids. Therefore, I would characterize the interaction between the enzyme and membrane as chemical in nature rather than as geometric. ... 

Structural information about the oxygenases provided limited insight into the mechanism (Schmidt et al. 2006). The crystallized enzyme from Synechocystis sp. PCC6803 is membrane associated and the interaction with the membrane is believed to be mediated by a nonpolar patch on the surface of the enzyme. This hydrophobic patch is thought to provide the necessary access of the protein to the membrane-bound carotenoids. Following withdrawal from the membrane, the substrate moves through the hydrophobic tunnel toward the metal center. The substrate orients the... 

Figure 9.15 Enzymes in aqueous (light-coloured) and hydrophobic (shaded) phases. (A) A protein in the periplasm (PP) of a cell (OM = outer membrane, CM = cytoplasmic membrane) (B) membrane-bound protein in a lipid bilayer (C) hydrophilic protein in an inverted micelle (D) interaction between enzyme and substrates in aqueous micelles (E) graph of catalytic activity as a function of micelle concentration.

A characteristic of virtually all methanogen hydrogenases is their very large native size (although they are soluble enzymes), typically 600-1000 kDa. This is often explained as a result of hydrophobic interactions with other proteins, and as an indication that it is a loosely-bound membrane protein. H2ase is often associated with membranes early during its purification [271,280]. These properties have been investigated in several ways by electron microscopy. 

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