A 52-year-old female is diagnosed with breast cancer. After discussing treatment options with her oncologist, she decides to turn to the Internet for advice. In a cancer survival chat room, she learns about laetrile, which is metabolized to cyanide. She begins taking laetrile, against medical advice, and develops progressive neuromuscular weakness of the upper and lower extremities, bilateral ptosis, and hypotension. The toxic effects of this unconventional anticancer agent are probably due to an inhibition of which of the following enzymes?

1. A)Guanylate cyclase
2. B)2,3-Bisphosphoglycerate mutase
3. C)Na+/K+-ATPase
4. D)Phosphofructokinase-2
5. E)Cytochrome oxidaseGABARITO