Eliasson, A, E Boles, B Johansson, M Österberg, J M Thevelein, I Spencer-Martins, H Juhnke, and B Hahn-Hägerdal. 2000. “Xylulose Fermentation by Mutant and Wild-Type Strains of Zygosaccharomyces and Saccharomyces Cerevisiae.” Appl. Microbiol. Biotechnol. 53 (4): 376–82. https://doi.org/10.1007/s002530051629.

The XK reaction was coupled with the pyruvate kinase reaction as follows:

xylulose + ATP ⟶ xylulose 5-phosphate + ADP ADP + phosphoenolpyruvate ⟶ pyruvate + ATP pyruvate + NADH ⟶ lactate + NAD�

The reaction mixture contained the following: 50 mM TRIS/HCl bufferr (pH 7.5), 2.0 mM MgCl2, 2.0 mM ATP, 0.2 mM phosphoenolpyruvate, 0.2 mM NADH, 10 U pyruvate kinase (E.C. 2.7.1.40), 10 U lactate dehydrogenase (E.C. 1.1.1.27) 8.5 mM xylulose.

Consumption of NADH was measured spectrophotometrically at 340 nm.

The molar absorption coefficient (extinction coefficient) of NADH at 340 nm (ε₃₄₀) is 6220 M-1 cm-1, whereas that of NAD⁺ at the same wavelength can be assumed to be 0.

The Beer-Lambert Law describes the linear relationship between the absorbance of a solution and the concentration of the absorbing species in the solution.

The equation is given by:

A = ε * c * l

where:

• A = Absorbance (no units)
• ε = Molar absorptivity or extinction coefficient (L·mol⁻¹·cm⁻¹)
• c = Concentration of the solution (mol·L⁻¹)
• l = Path length through the sample (cm)

• Absorbance (A) is the amount of light absorbed by the solution.
• Molar absorptivity (ε) is a constant that depends on the nature of the absorbing species and the wavelength of light.
• Concentration (c) is the amount of the absorbing species per unit volume.
• Path length (l) is the distance that light travels through the solution.

The Beer-Lambert Law is often used in spectrophotometry to determine the concentration of a solute in a solution by measuring the absorbance.

The concentration of protein in the extract was 2.6 mg/mL.

U / mg of protein

One unit of enzyme activity is defined as 1 µmol of substrate converted per min.

0.6U / mg protein