Question

1) The mental retardation associated with PKU can be avoided if patients are placed on a low phenylalanine diet for the early years, and perhaps for life.

a) Why is a PKU patient placed on a low phenylalanine diet instead of a phenylalanine free diet?

b) The artificial sweetener Nutrasweet ® contains the compound aspartame, which consists of a 
methylated Asp-Phe dipeptide. (The C-terminal carboxyl group is methylated.) Draw the structure of aspartame. If you were a physician, what advice would you give to a PKU patient regarding this product? If you were a manufacturer of aspartame, what would your responsibility to your customers be?

Answer 1

a) PKU patient is placed on a low phenylalanine diet because phenylalaine is an essential amino acid which can not be made by a human body. Therefore small amounts of phenylalanine has to be supplied in the body.

b)

Aspartame is an artificial sweetener which is a methylated ester of aspartic acid-phenylalanine dipeptide. Phenylalanine hydroxylase enzyme can breakdown aspartame to release free phenylalanine which could increase the blood levels of phenylalanine and could be dangerous for the body. Therefore, as a physician I would advice to strictly avoid aspartame. As a manufacturer I would clearly write on the product that it is NOT for phenylketonuria patients.