In the Oliver-Rosalki CK determination method, which reaction uses hexokinase and G6PD along with CK?

• A. Reverse reaction
• B. Forward reaction
• C. Both reverse and forward
• D. None

Answer: (A)

The key idea is linking CK activity to a measurable NADPH signal through a coupled enzyme system. In this kit, CK activity is assessed by what ATP is produced or consumed in its reaction, because that ATP is then used by downstream enzymes to generate a detectable product.

When CK runs in the forward direction, phosphocreatine and ADP are converted to creatine and ATP. That ATP is immediately used by hexokinase to phosphorylate glucose, forming glucose-6-phosphate and ADP. Glucose-6-phosphate is then acted on by glucose-6-phosphate dehydrogenase with NADP+, producing NADPH. The rate at which NADPH appears is proportional to the rate of CK activity in the forward direction, so the trio of enzymes (CK, hexokinase, G6PD) together monitor CK by this forward reaction.

If CK were to run in reverse, it would consume ATP to form phosphocreatine and ADP, which wouldn’t drive the hexokinase/G6PD step in the same straightforward, stoichiometric way. Therefore, the coupling with hexokinase and G6PD is designed to reflect CK activity in the forward reaction.