Abstract
Using the Thunberg's methylenblue technique, the following points were noticed.
1. The lactic acid dehydrogenase system (washed pig's heart muscle -f-coferment) a number of a-oxy acids such as malic-, tartaric and a-oxyglutaric acid can be as well oxidized as lactic acid.
2. Of the optical isomers d-lactic acid only can be oxidized, while l-lactic acid remains inactive. With regard to tartaric acid, l-form is rather active, while d-form is not. Of malic acid, both forms are active.
3. Fumaric- and maleic acids also can be well oxidized by this system, but with the latter, coferment is not indispensable.
4. Oxalic- and malonic acid are powerful inhibiters for lactic acid oxidation by this system but not so much so for malic acid.
5. Esterification of lactic acid renders the acid quite inactive.
