LDH Assay Substrate Solution

Recipe

l-(+)-lactic acid	0.054 m
β-NAD⁺	1.3 mm
2-p-iodophenyl-3-p-nitrophenyl tetrazolium chloride (INT) solution	0.66 mm
1-methoxyphenazine methosulfate (MPMS) solution	0.28 mm
Tris–HCl buffer (pH 8.2)	0.2 m
Dissolve the ingredients in 0.2 m Tris–HCl buffer (pH 8.2). One milliliter of assay substrate is needed for 20 reactions.
Over time, competitive inhibitors of LDH can form in phosphate solutions of NADH. Prepare the LDH assay substrate solution fresh from stock solutions each time.