Creatine kinase (CK) catalyzes the reaction between creatine phosphate (CP) and adenosine 5'-diphosphate (ADP), forming creatine and adenosine 5'-triphosphate (ATP). The latter converts glucose to glucose-6-phosphate (G6P) in the presence of hexokinase (HK). G6P is oxidized to gluconate-6P in the presence of reduced nicotinamide adenine dinucleotide phosphate (NADP), catalyzed by glucose-6-phosphate dehydrogenase (G6PDH). The conversion is kinetically monitored at 340 nm through the increase in absorbance resulting from the reduction of NADP to NADPH, proportional to CK activity in the sample. The inclusion of N-acetylcysteine (NAC) in this method allows optimal enzyme activation.
