A kinetic procedure for the estimation of arginine in serum using arginine kinase.

A method for estimation of arginine in 50 microliters serum was developed using commercially available arginine kinase (EC 2.7.3.3). The assay is based on the transformation of arginine and ATP into phospho-arginine and ADP by the enzyme. ADP is measured by two coupling reactions involving pyruvate kinase (EC 2.7.1.40) and lactate dehydrogenase (EC 1.1.1.27) with measurement of NADH consumption at 340 nm. The method involves preincubation of serum in the reaction medium without arginine kinase to eliminate side reactions and a kinetic rate protocol with measurements of absorbance at 60 s and 180 s. Reaction temperature is 30 degrees C. The reaction is linear up to at least 3 mmol/l of arginine. Within-batch CV is less than 3% for arginine levels above 0.75 mmol/l and the between-batch CV is 6.5% or less. The method correlates well with an automatic amino acid analyzer procedure (r = 0.983). The reference range derived from sera of 40 blood donors has been determined to be 0.06-0.20 mmol/l.