A 34-year-old man comes to the emergency department due to a facial injury. He reports getting hit on the face during a fistfight at a bar. Examination shows dark blue periorbital ecchymosis on the right side. Ophthalmic and neurologic examinations are otherwise normal. After appropriate evaluation, the patient is discharged home. Several days later, the bruise becomes greenish in color. This change in color is best explained by the activity of which of the following enzymes?

Question

A 34-year-old man comes to the emergency department due to a facial injury.  He reports getting hit on the face during a fistfight at a bar.  Examination shows dark blue periorbital ecchymosis on the right side.  Ophthalmic and neurologic examinations are otherwise normal.  After appropriate evaluation, the patient is discharged home.  Several days later, the bruise becomes greenish in color.  This change in color is best explained by the activity of which of the following enzymes?

Quizplus · Accepted Answer

11ec160b_36e4_37de_9249_118b19e8c0e9_MD0001_00 This patient has a resolving hematoma after a traumatic injury. Following the injury, hemoglobin-containing erythrocytes escape into the periorbital tissues, giving the bruise its initial purple or bluish color. Erythrocyte destruction causes the release of iron-containing heme molecules. Heme oxygenase (contained in macrophages, among other cells) degrades heme into biliverdin, carbon monoxide, and ferrous iron while consuming oxygen and electrons provided by NADH and NADPH-cytochrome P450 reductase. Biliverdin is green in color and is further reduced (by the enzyme biliverdin reductase) to the yellow pigment bilirubin, which is then transported to the liver bound to albumin. (Choice A) Bilirubin glucuronyl transferase, or uridine 5'-diphospho-glucuronyl transferase (UGT), is the enzyme necessary for bilirubin conjugation to glucuronic acid. Lack of UGT or the use of medications that interfere with its activity impairs the liver's ability to conjugate bilirubin. (Choices B, D, and E) Ferrochelatase (inhibited by lead) is the final enzyme in the heme synthetic pathway. Porphobilinogen deaminase (PBG deaminase) and uroporphyrinogen decarboxylase (UROD) are also involved in heme production, not degradation; UROD deficiency can be seen in porphyria cutanea tarda, the most common porphyria, and PBG deaminase deficiency can be seen in acute intermittent porphyria. Educational objective: Heme oxygenase converts heme to biliverdin, a pigment that causes the greenish color to develop in bruises several days after an injury.

A 34-Year-Old Man Comes to the Emergency Department Due to a Facial