Papain-mediated reduction of MTT is an artifact but not an indicator of cell apoptosis in Saccharomyces cerevisiae

ABSTRACT

Papain is a proteolytic enzyme of the cysteine protease family used for tissue dissociation and cell separation. Papain’snonspecific proteolysis of the plasma membrane enzymes plays a crucial role in the homeostasis by disrupting theintracellular pH of the affected cells which might lead to cell death. When the Saccharomyces cerevisiae cellswere treated with different concentrations of papain (1.0, 5.0, 10.0, 20.0, and 30.0 µg/ml), we found no alterationin the trans-plasma membrane electron transport (TPMET) activity and the intracellular pH of the cells, while itsignificantly decreased the mitochondrial dehydrogenase activity when measured by 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay. Additional verification of cell viability by trypan blue assay showed98%–99% cell viability, contrary to the higher cell death observed with MTT assay. To better understand the decreasein cell viability with MTT assay, we tested the cell-free system that demonstrated a significant decrease of MTTconcentration but the trypan blue assay showed more number of viable cells. This study shows that papain interfereswith the MTT assay.