The lactic dehydrogenase of Propionibacterium pentosaceum

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Abstract
Preparations capable of oxidizing lactate to pyruvate in the presence of suitable hydrogen acceptors were obtained from Propionibacterium pentosaceum, by grinding frozen cells with alumina, followed by extraction with dilute phosphate buffer. Several assay methods are described and a purification procedure is presented whereby a 15-fold concentration of the activity is obtained. The requirements for half-saturation of the enzyme were found to be: D-([long dash])-lactate (51.6 [mu][image]), phenazine methosulphate (0.64 m[image]). The enzyme had infinite affinity for methylene blue, 2:6-dichloropheno-lindophenol and l:2-naphthaquinone-4-sulphonate. The optimum pH for lactate oxidation was found to be 7.7 at 30[degree]C. The preparations are activated by NH+4, CN-, F-, Mg2+ ions and malonate and are thermo-labile. The preparations are inhibited by pyruvate, oxalate, thiol reagents, narcotics, quinacrine, chloroquine, quinine, dicoumarol, vitamin K1, pentachlorophenol, thyroxine and hydrazine. The inhibition of quinacrine is reversed by perchloric acid extracts obtained from the purified enzyme, but not by boiled juices prepared from it or by flavinadenine dinucleotide or flavin mononucleotide. The effect of pH on the inhibition by quinacrine and dicoumarol was studied.