In the ultraviolet procedure for quantifying uric acid, what does the reaction between uric acid and uricase cause?

In the ultraviolet procedure for quantifying uric acid, what does the reaction between uric acid and uricase cause?

• A. Nicotinamide adenine dinucleotide (NADH)
• B. Allantoin
• C. An increase in absorbance
• D. Reduction of phosphotungstic acid

Answer: (B)

Uricase specifically converts uric acid into allantoin. In the ultraviolet procedure, the measurement hinges on this enzymatic reaction: as uric acid is oxidized to allantoin, the UV-absorbing uric acid is consumed, causing a decrease in absorbance at 293 nm. The signal you monitor comes from the disappearance of uric acid, and the actual product of the reaction is allantoin. The other possibilities—NADH formation, a direct increase in absorbance, or reduction of phosphotungstic acid—do not describe what uricase does in this assay.

Uricase specifically converts uric acid into allantoin. In the ultraviolet procedure, the measurement hinges on this enzymatic reaction: as uric acid is oxidized to allantoin, the UV-absorbing uric acid is consumed, causing a decrease in absorbance at 293 nm. The signal you monitor comes from the disappearance of uric acid, and the actual product of the reaction is allantoin. The other possibilities—NADH formation, a direct increase in absorbance, or reduction of phosphotungstic acid—do not describe what uricase does in this assay.