Physicochemical properties and purification of malate dehydrogenase

Physicochemical properties and purification of malate dehydrogenase MDase, as an enzyme of the citric cycle, is ubiqui- 

MDase is composed of 2 identical subunits of about 35000 daltons which are held together by secondary interactions. The 2 subunits have equivalent binding sites for NAD+ (Holbrook and Wolfe, 1972) and each subunit binds a coenzyme. These subunits can dissociate without losing catalytic activity and reassemble in the presence of substrate (Shore and Chakrabarti, 1976 Bleile et al., 1977). The enzyme contains 14 SH groups, two of which are required to bind substrate (Sequin and Kosicki, 1967). 

Commercial preparations are supplied as (NH4)2S04 precipitates with a specific activity of about 1000 U/mg with oxaloacetate as substrate and are stable for at least a year at 4°C. Once dialyzed against phosphate buffer, it should be stored at — 20°C. 

The earliest purification procedures used fractionation with 

Inhibitors oxaloacetate, S-hydroxyquinoline , adenine (AMP, ADP, ATP) , sulphite, thyroxine , phenols and substituted phenols  

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