CASE FILES: BIOCHEMISTRY
C O M P R E H E N SIO N Q U E ST IO N S
[43.1] A patient presents with extreme swelling and tenderness in the joints
of the extremities. Examination of synovial fluid extracted from the big
toe reveals the presence of urate crystals and confirms the diagnosis of
gouty arthritis. The drug allopurinol is prescribed to inhibit which of
the following enzymes?
A. Adenosine deaminase
B. AMP deaminase
C. Nucleoside phosphorylase
E. Xanthine oxidase
[43.2] Hyperuricemia (gout) is a clinical condition characterized by elevated
levels of uric acid that lead to the formation of sodium urate crystals
that are found primarily in the joints of the extremities. Which of the
following factors contributes most to the formation of urate crystals in
A. Decreased blood flow
B. Decreased temperature
C. Exposure to sunlight
D. Increased blood flow
E. Increased mobility
[43.3] Inherited defects in components of purine catabolism and salvage are
associated with various conditions and syndromes. The enzyme
hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is a key
enzyme in the purine salvage pathway. It is responsible for reforming
IMP and GMP from hypoxanthine and guanine, respectively. In this
manner purine bases are salvaged back into the purine nucleotide pool.
Genetic defects that lead to the loss of HGPRT activity are the primary
cause for which of the following conditions?
B. Lesch-Nyhan syndrome
C. Orotic aciduria
D. Severe combined immunodeficiency syndrome
E. Tay-Sachs disease
A nsw ers
E. One approach for the treatment of gout is to decrease the levels of
uric acid production to prevent the development of urate crystals.
Allopurinol is an inhibitor of xanthine oxidase enzymatic activity. The
administration of allopurinol is an effective treatment of gout because
it decreases the amount of uric acid produced, which in turn alleviates
the formation of sodium urate crystals.