The GLDH-coupled method for ammonia determination uses which cofactor with glutamate?

The GLDH-coupled method for ammonia determination uses which cofactor with glutamate?

• A. NAD
• B. FAD
• C. NADP
• D. CoA

Answer: (A)

Glutamate dehydrogenase uses the nicotinamide adenine dinucleotide cofactor to shuttle electrons in the ammonia–α-ketoglutarate–glutamate reaction. In the GLDH-based ammonia assay, ammonia reacts with α-ketoglutarate in the presence of NAD+ (the oxidized form) to form glutamate, with NAD+ being reduced to NADH (the amount of NADH formed or consumed is measured spectrophotometrically, typically at 340 nm). This direct involvement of the NAD+/NADH couple is why NAD (NAD+) is the correct cofactor for this method. NADP+, FAD, and CoA participate in other enzyme systems, but they are not the cofactors used by GLDH in this ammonia determination.

Glutamate dehydrogenase uses the nicotinamide adenine dinucleotide cofactor to shuttle electrons in the ammonia–α-ketoglutarate–glutamate reaction. In the GLDH-based ammonia assay, ammonia reacts with α-ketoglutarate in the presence of NAD+ (the oxidized form) to form glutamate, with NAD+ being reduced to NADH (the amount of NADH formed or consumed is measured spectrophotometrically, typically at 340 nm). This direct involvement of the NAD+/NADH couple is why NAD (NAD+) is the correct cofactor for this method. NADP+, FAD, and CoA participate in other enzyme systems, but they are not the cofactors used by GLDH in this ammonia determination.