Question 28.1: The blood serum concentration of the transaminase from heart...

The blood serum concentration of the transaminase from heart muscle, aspartate aminotransferase (AST), is used in the diagnosis of heart disease because the enzyme escapes into the serum from damaged heart cells. AST catalyzes transamination of aspartate with α-ketoglutarate. What are the products of this reaction?

ANALYSIS The reaction is the interchange of an amino group from aspartate with the keto group from α-ketoglutarate. We know that α-ketoglutarate always gives glutamate in transamination, so one product is glutamate. The product from the amino acid will have a keto group instead of the amino group; we need to consider various amino acid structures to identify a candidate. Consulting Table 18.3 (which lists the 20 protein amino acid structures), we see that the structure of aspartate (aspartic acid) is

Removing the  -NH_3  ^+ and — H groups bonded to the carbon and replacing them by a  = O gives the desired acid, which in this case happens to be oxaloacetate: