Oxidative stress and the role of novel thiol compounds at fertilization.

A new class of thiols, the 1-methyl-4-mercaptohistidines, has been found in high concentrations in invertebrate eggs. This family, called the ovothiols, has unusual redox properties, including the ability to confer a CN- -resistant NAD(P)H oxidase activity on ovoperoxidase, the enzyme that catalyzes the physiological crosslinking of the fertilization envelope with dityrosine residues. Ovothiol has a redox potential of 44 mV positive to glutathione and thus is maintained in the reduced state in eggs by reduced glutathione, without the need for an ovothiol reductase. We propose that high concentrations of reduced ovothiol are present in eggs to protect them from the oxidative stress caused by the respiratory burst of fertilization.