What is the secondary enzymatic reaction coupled to the urease reaction in the ultraviolet enzymatic method for BUN?

The secondary enzymatic reaction coupled to the urease reaction in the ultraviolet enzymatic method for determining Blood Urea Nitrogen (BUN) is indeed glutamate dehydrogenase. In this method, urease catalyzes the hydrolysis of urea into ammonia and carbon dioxide. The ammonia produced is then incorporated into a secondary reaction where glutamate dehydrogenase plays a critical role.

In the presence of α-ketoglutarate, glutamate dehydrogenase catalyzes the conversion of ammonia and α-ketoglutarate into glutamate. This reaction is often linked with NADH oxidation, where the consumption of NADH can be measured spectrophotometrically. The change in absorbance correlates with the amount of urea present in the sample, allowing for the quantification of BUN.

This coupling enhances the specificity and sensitivity of the method by ensuring that the ammonia generated from the urease reaction is effectively converted and measured in relation to other metabolites, allowing for accurate assessment of renal function.