CASE FILES: BIOCHEMISTRY
C. In addition to being an important cofactor for the enzymes involved
in the oxidative decarboxylation of pyruvate, a-ketoglutarate, and
branched-chain a-ketoacids, thiamine is also a cofactor for the enzyme
transketolase, the enzyme that transfers a glycoaldehyde group from
a ketose sugar to an aldose sugar in the pentose phosphate pathway.
One of the diagnostic tools in determining a thiamine deficiency is
determination of the activity of red blood cell transketolase in the
presence and absence of added thiamine. A thiamine deficiency
would be expected to increase blood lactate concentrations. A defi-
ciency of biotin would lead to decreased carboxylase activity,
whereas an increased methylmalonate concentration would be
observed with a deficiency in vitamin B12. A deficiency in vitamin K
would lead to an increase in prothrombin time.
B IO C H E M IS T R Y PE A R L S
Thiamine (vitamin B1) is an important water-soluble vitamin that, in
its active form of thiamine pyrophosphate, is used as a cofactor in
enzymatic reactions that involve the transfer of an aldehyde group.
Thiamine deficiency is uncommon except in alcoholics who, as a
consequence of nutritional deficiencies and malabsorption, may
The classic clinical triad of dementia, ataxia (difficulty with walking),
and eye findings may be seen, but more commonly, only forget-
fulness is noted.
Thiamine pyrophosphate is also an important cofactor for many
dehydrogenase reactions as well as the transketolase reactions in
the pentose phosphate pathway of carbohydrate metabolism.
Murray RK, Granner DK, Mayes PA, et al. Harper’s Illustrated Biochemistry,
26th ed. New York: Lange Medical Books/McGraw-Hill, 2003.
Wilson JD. Vitamin deficiency and excess. In: Fauci AS, Braunwald E, Isselbacher
KJ, et al., eds. Harrison’s Principles of Internal Medicine, 14th ed. New York: