<prompt> Lack of Homogentisate oxidase enzyme causesPhenylketonuriaAlkaptonuriaMaple syrup urine diseaseHomocystinuria  <response>: B Alkaptonuria ALKAPTONURIA: The defective enzyme in alkaptonuria is homogentisate oxidase in tyrosine metabolism. Homogentisate accumulates in tissues blood, gets oxidized to the corresponding quinones, which polymerize to give black or brown colour. For this reason, the urine of alkaptonuric patients resembles coke in colour. 