UV enzymatic method
Creatine kinase (CK) catalyzes the reaction between creatine phosphate (CP) and adenosine 5´-diphosphate (ADP) with formation of creatine and adenosine 5´-triphosphate (ATP). The latter phosphorylates glucose to glucose-6-phosphate (G6P) in the presence of hexoquinase (HK). G6P is oxidized to Gluconate-6P in the presence of reduced nicotinamide-adenine dinucleotide phosphate (NADP) in a reaction catalyzed by glucose-6-phosphate dehydrogenase (G6P-DH).
The conversion is monitored kinetically at 340 nm by the rate of increase in absorbance resulting from the reduction of NADP to NADPH proportional to the activity of CK present in the sample.
In this test the presence of N-acetilcysteine (NAC) allows the optimal activation of the enzyme.