<prompt> Deficiency of which of the following enzyme leads to toxicity of 5-fluorouracil?Purine nucleoside phosphorylaseDihydropyrimidine dehydrogenasePRPP synthaseAdenosine deaminase  <response>: 5-fluorouracil is acted upon by dihydropyrimidine dehydrogenase - Deficiency - accumulation of 5-FU - toxicity. 