Plasma membrane thiol group oxidation

Copper is part of several essential enzymes including tyrosinase (melanin production), dopamine beta-hydroxylase (catecholamine production), copper-zinc superoxide dismutase (free radical detoxification), and cytochrome oxidase and ceruloplasmin (iron conversion) (Aaseth and Norseth 1986). All terrestrial animals contain copper as a constituent of cytochrome c oxidase, monophenol oxidase, plasma monoamine oxidase, and copper protein complexes (Schroeder et al. 1966). Excess copper causes a variety of toxic effects, including altered permeability of cellular membranes. The primary target for free cupric ions in the cellular membranes are thiol groups that reduce cupric (Cu+2) to cuprous (Cu+1) upon simultaneous oxidation to disulfides in the membrane. Cuprous ions are reoxidized to Cu+2 in the presence of molecular oxygen molecular oxygen is thereby converted to the toxic superoxide radical O2, which induces lipoperoxidation (Aaseth and Norseth 1986). 

Alterations in the cytoskeleton. The cytoskeleton depends on the intracellular Ca2+ concentration, which affects actin bundles, the interactions between actin and myosin and a-tubulin polymerization. The effect of increases in Ca2+ on the cytoskeletal attachments to the plasma membrane and the role of the cytoskeleton in cellular integrity have already been mentioned (see above). If the cytoskeleton is damaged or disrupted or its function altered by an increase in Ca2+, then blebs or protrusions appear on the plasma membrane (see below). As well as an increase in Ca2+, oxidation of, or reaction with sulfydryl groups, such as alkylation or arylation, for example, may disrupt the cytoskeleton, as thiols... 

The data summarized here provide preliminary evidence for regulation of phytoalexin accumulation by thiol and/or disulfide groups In the interior of the plasma membrane. A hypothesis Is proposed oxidation state of the membrane SH groups regulating the phytoalexin response Is maintained by biological thiol/ disulfide ratios in the cytoplasm and by accessibility of these compounds to the membrane SH moieties. 

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