Effect of storage temperature on the activity of submitochondrial particles

The submitochondrial particle (SMP) assay employs processed mammalian mitchondria to assess the toxicity of chemical contaminants in aqueous solutions. Particles and associated reagents are commercially available to support two individual procedures, the electron transfer (ETr) and reverse electron transfer (RET) assays. The objective of the present study was to assess the effect of storage temperature on SMP activity. One RET and one ETr assay were conducted with sodium dodecylsulfate on each of two vials of particles stored at -20 and -80 degrees C at periodic intervals over a six-month span. Results demonstrated that SMP could remain active in either assay through six months of storage at either temperature. However, there were isolated vials of particles stored at -20 degrees C that exhibited unacceptable reductions in activity for both the ETr and the RET assays that were not related to storage duration. These results were used to develop guidance in assessing the acceptability of particle activity in SMP assays.