To cross the blood brain barrier, different molecules often utilize the same tra

Question

To cross the blood brain barrier, different molecules often utilize the same transport protein and thus compete for transport into the brain. Below are the kinetics of C14 3-HBA transport in the presence and absence of glucose and the branched chain keto acid, keto-methylvalerate. Interpret the results in regard to glucose and keto-methylvalerate transport into the brain.

In the metabolic disorder, Maple Syrup Urine Disease, patients have a mutation in the enzyme branched-chain alpha-keto acid dehydrogenase, which leads to accumulation of branched chain keto acids, including keto-methylvalerate in the blood/circulation. What would the effect of this mutation be on critically needed ketone body, specifically 3-HBA, transport into the brain during times of prolonged fasting when blood glucose levels are low?

Explanation / Answer

Transport of HBA is reduced in presence of methylvalerate. During fasting state the body uses a ketone body, 3-hydroxybutyric acid as an energy source. Now, if due to presence of methylvalerate, 3HBA is reduced in blood. So, brain will not get enough energy for carrying out it's usual functions.

Maple syrup urine disease is autosomal recessive disorder. Infants born with this disorder are healthy initially but later on show retarded growth. Their brain, which is unable to get 3HBA deteriorates slowly and steadily finally leading to death.

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