Garrod's information about the enzyme alteration resulting in alkaptonuria led to further understanding of these types of metabo
lic pathways in humans. phenylketonuria (pku) occurs when another enzyme in the pathway is altered or missing, resulting in a failure of phenylalanine (phe) to be metabolized to another amino acid: tyrosine. tyrosine is an earlier substrate in the pathway altered in alkaptonuria. how might pku affect the presence or absence of alkaptonuria?
The answer would be: It would have no effect, because tyrosine is also available from the diet
The pathway is different, alkaptonuria increased tyrosine is caused by decreased usage. In phenylketonuria, it is caused by increased production. While tyrosine is increased in phenylketonuria patient, it won't cause alkaptonuria because tyrosine could be found in the diet.
