New findings on serum lactate dehydrogenase isoenzymes in pigs during slaughter

: In the article we describe lactate dehydrogenase-(LD) (EC 1.1.1.27) isoenzyme pattern detected in the sera of pigs at slaughter. The pattern was different from that of normal serum (Fig. 1) and was characterized by the occurrence of an extra LD-fraction in the cathodic site of LD4 (Fig. 2). This fraction was unusual due to its unwillingness to separate by native polyacrylamide gel electrophoresis (PAGE) and took shape of a diffuse zone. The presence of the extra LD-zone caused a proportional decrease in quantitative distribution of the other LD forms, especially LD1 to LD3, in slaughtered pig sera (Tab. I). We examined the homogeneity of an apparent LD5-fraction using gel isoelectric focusing (IEF). We found out that after separation in a gradient of pH (3-9) two to three new extra bands with LD activity appeared in the area with relatively high pH value (pH 9) (Fig. 3). Their localization in the gradient of pH was greatly different from that of true LD molecules, the latter being situated in more acidic area. It is obvious from the finding described above that the diffuse LD-zone, detected in the serum of pigs at slaughter by native PAGE, was in no case a homogeneous protein. Consequently, it eliminates a possibility that the extra LD fraction reflects an increased LD5 activity in serum of affected animals. On the contrary, the IEF showed that the diffuse LD-zone consisted of two to three electrophoretically distinct proteins with relatively high pI values. As these proteins differed in their electrophoretic properties from the true LD isoenzymes we denoted them LD-like proteins. An origin of the unusual LD-like proteins detected in the serum of pigs at slaughter remains unknown for us for the time being.