Table 1.

Troubleshooting guide for inorganic arsenic methylation in rat liver cytosol assay system

Problem	Cause	Solution
Donor liver is not cleared of blood	Inadequate perfusion	Reposition cannula in inferior vena cava to improve perfusion.
Turbid cytosolic fraction	Inadequate removal of lipid layer before harvesting of cytosol	Remove lipid layer with curved tip Pasteur pipette before harvesting of cytosol.
Low methylation activity in in vitro assay system	Loss of methylation activity in cytosolic fraction	Examine composition of assay system. Assure presence of GSH in all buffers used for preparation of cytosolic fraction and in assay system. Solutions containing AdoMet used in this assay are not stable for storage and should be prepared immediately before use.