Organic Chemistry

1058 CHAPTER 25 The Organic Mechanisms of the Coenzymes • Metabolism

Without phenylalanine hydroxylase, the level of phenylala-

nine builds up, and when it reaches a high concentration, it is

transaminated to phenylpyruvate. The high level of phenylpyru-

vate found in urine gave the disease its name.

+NH 3

CH 2 CHCOO−

phenylalanine

phenylalanine

hydroxylase

O

CH 2 CCOO−

O

OO

CH 2 CCOO−

phenylpyruvate

+NH 3

+NH 3

OH

CH 2 CHCOO−

CH 2 CHCOO−

HO

HO

HO

tyrosine

dihydroxyphenylanine

dopa

HO CH 2 CH 2 NH 3

HO

dopamine

melanin

CH 2 COO−

C CCH 2 CCH 2 COO−

HO

HO

OH

para-hydroxyphenylpyruvate

para-hydroxy-

phenylpyruvate

dioxygenase

H

H C COO−

homogentisate

fumarate + acetyl-CoA

homogentisate

dioxygenase

tyrosine

aminotransferase

+

HO CHCH 2 NH 3

HO

norepinephrine

noradrenaline

+

OH

HO CHCH 2 NH 2 CH 3

HO

epinephrine

adrenaline

+

PHENYLKETONURIA: AN INBORN

ERROR OF METABOLISM

Tyrosine is a nonessential amino acid because the

body can make it by hydroxylating phenylalanine. About 1 in

every 20,000 babies, however, is born without phenylalanine

hydroxylase, the enzyme that converts phenylalanine into tyro-

sine. This genetic disease is called phenylketonuria (PKU).

HEART ATTACKS: ASSESSING

THE DAMAGE

Damage to heart muscle after a myocardial infarc-

tion (a heart attack) allows aminotransferases and other enzymes

to leak from the damaged cells of the heart into the bloodstream.

Following a heart attack, the severity of damage done to the heart

can be determined from the concentrations of alanine amino-

transferase and aspartate aminotransferase in the bloodstream.