Which glucose method catalyzes the phosphorylation of glucose by ATP, forming glucose-6-phosphate and adenosine diphosphate with the absorbance of the NADPH product read at 340 nm?

Which glucose method catalyzes the phosphorylation of glucose by ATP, forming glucose-6-phosphate and adenosine diphosphate with the absorbance of the NADPH product read at 340 nm?

• A. o-Toluidine
• B. Glucose oxidase
• C. Hexokinase
• D. Glucose dehydrogenase

Answer: (C)

The main idea being tested is how a glucose assay uses a two-enzyme, ATP-dependent step to link glucose concentration to a measurable NADPH signal. The process starts with hexokinase, which transfers a phosphate from ATP to glucose, producing glucose-6-phosphate and ADP. This phosphorylation traps glucose in a form that can be further processed in the pathway. The glucose-6-phosphate is then acted on by glucose-6-phosphate dehydrogenase, which oxidizes it while reducing NADP+ to NADPH. The amount of NADPH formed correlates with the amount of glucose and is read by measuring absorbance at 340 nm, where NADPH strongly absorbs light. So, the enzyme that initiates this sequence by phosphorylating glucose with ATP is hexokinase, making it the correct choice. The other methods don’t involve a phosphorylation step with ATP coupled to NADPH readout: o-toluidine-based assays are colorimetric for sugars but don’t rely on ATP phosphorylation with NADPH; the glucose oxidase method uses oxygen and produces hydrogen peroxide rather than generating NADPH; and the glucose dehydrogenase approach relies on NAD+/NADH without the ATP-driven phosphorylation step.

The main idea being tested is how a glucose assay uses a two-enzyme, ATP-dependent step to link glucose concentration to a measurable NADPH signal. The process starts with hexokinase, which transfers a phosphate from ATP to glucose, producing glucose-6-phosphate and ADP. This phosphorylation traps glucose in a form that can be further processed in the pathway. The glucose-6-phosphate is then acted on by glucose-6-phosphate dehydrogenase, which oxidizes it while reducing NADP+ to NADPH. The amount of NADPH formed correlates with the amount of glucose and is read by measuring absorbance at 340 nm, where NADPH strongly absorbs light.

So, the enzyme that initiates this sequence by phosphorylating glucose with ATP is hexokinase, making it the correct choice. The other methods don’t involve a phosphorylation step with ATP coupled to NADPH readout: o-toluidine-based assays are colorimetric for sugars but don’t rely on ATP phosphorylation with NADPH; the glucose oxidase method uses oxygen and produces hydrogen peroxide rather than generating NADPH; and the glucose dehydrogenase approach relies on NAD+/NADH without the ATP-driven phosphorylation step.