So once again, one property of reduced nicotine amide adenine dinucleotide, NADH, is that it has the ability to absorb light of a specific wavelength, 340 nm. Therefore, we can monitor the activity of the enzyme indirectly by examining how much light is absorbed by that solution. And this is shown in the following diagram. So in this diagram, these red dots are basically the NAD plus molecules, and these blue figures are the lactate. So we take this solution and we add the enzyme sample into our solution. And if one of the enzymes in that sample is lactate dehydrogenase, then these blue figures will be converted into these purple Pyruvate molecules.