Surface denaturation, protection against

In the experiments with galactose oxidase and dopamine -monooxygenase very low enzyme concentrations have often been used. The addition of an inert protein might help to approximate the natural conditions by providing a protection against surface denaturation and against radicals, and by regulating the trace metal concentrations. 

Fig. 10.9 Schematic representation of molecular machineries that confer acetic acid resistance in Acetobacter and Gluconacetobacter. (Schematic diagram quoted from Nakano and Fukaya 2008) THBH and phosphatidylcholine on the membrane and polysaccharide on the surface of the cells are suggested to be involved in acetic acid resistance. Acetic acid, which penetrates into the cytoplasm, is assumed to be metabolized through the TCA cycle by the actions of enzymes typical for AAB. Furthermore, intracellular acetic acid is possibly pumped out by a putative ABC transporter and proton motive force-dependent efflux pump using energy produced by ethanol oxidation or acetic acid overoxidation. Intracellular cytosolic enzymes are intrinsically resistant to low pH and are protected against denaturation by stress proteins such as molecular chaperones. ADH membrane-bound alcohol dehydrogenase, ALDH membrane-bound aldehyde dehydrogenase, CS citrate synthase, ACN aconitase, PC phosphatidylcholine...

The ability of Ca2+ to crosslink groups and so stabilize proteins against thermal denaturation or hydrolytic attack is well illustrated by thermolysin, which involves four Ca2+ and a catalytic Zn2+. The function of the calcium is to stabilize the protein structure.404 Calcium also protects surface protein of the neural retina from tryptic cleavage.405... 

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