Initially, it was claimed that Laetrile kills tumor cells through the action of the enzyme beta-glucosidase. Beta-glucosidase splits compounds sych as amygdalin in which two sugars are joined in a glucoside bond. In this theory of Laetrile's action the action of beta-glucosidase releases mandelonitrile, which produces cyanide, killing nearby cells. These two factors would cause a buildup of cyanide around cancer cells. However, neither of these assertion is true.
Analysis shows only traces of beta-glucosidase in animal tissues.
Moreover, rhodanese levels are equal in normal and cancerous tissues. If this were true, the compound devised by Krebs, Jr. in 1952 would release cyanide in cancer tissues, since it contains a glucoronide bond. There are two fallacies to this thesis, however. Second, this theory is irrelevant to the preparations of Laetrile used, which contain amygdalin. Beta-glucuronidase does not act on amygdalin, because that substance contains a glucoside bond.