Figure 2

Phosphate acetyltransferase activity of Mycoplasma hyorhinis can be confused with citrate synthase activity of cultured skin fibroblasts contaminated by M. hyorhinis . A: Measurement of the citrate synthase activity before (a) and after (b) treatment showing, before oxaloacetate addition, the rapid reduction of DTNB in the mycoplasma-contaminated fibroblasts as compared to treated cells. The experiment was started with the addition of Triton X100-permeabilized fibroblasts and DTNB followed by the addition of acetylCoA and oxaloacetate. B: Measurement of the DTNB reduction in mycoplasma-contaminated cells in the presence (d) or absence of phosphate (c) in the medium. The experiment started with the addition of cells and DTNB, followed by the addition of acetyl-CoA. In b and c, 10 mM phosphate was later added to the cuvette. Numbers along the traces are nmol DTNB reduced/min/mg protein and represent mean values of experiments carried out independently on the 4 different cell lines. Rather large standard variations (between 20 to 30%) were calculated presumably reflecting variable level of cell contamination by M. hyorhinis (not shown).