Under acidic conditions in particular, such as those experienced by cancer patients, homocysteine can cyclize upon itself to form its thiolactone. This can then dimerize and react with nucleophilic groups on protein (N,S,O) to coat the protein in ways chemically mimicking vitalethine. Chemical similarities between the beneficial vitalethine and toxic homocysteine are uncanny, right down to their respective abilities to tautomerize between two structures. Homocysteine may be toxic simply due to this ability to mimic and interfere with reactions that otherwise are controlled by vitalethine and its monooxygenase receptor. Attachment to protein also is a time-honored way to make antibodies, with associated nightmarish potentials for inadvertently triggering autoimmunity.