XenoTech: Uncommon Science, Uncommon Service
XenoTech is dedicated to providing the highest quality GLP in vitro drug metabolism and drug-drug interaction studies to pharmaceutical and chemical companies worldwide.
We are the leading provider of a variety of in vitro tools including hepatocytes, microsomes, S9 fraction, recombinant CYPs, transporter membranes, substrates and metabolites and antibodies against Cytochromes P450.
Selected Frequently Asked Questions
How can I check for P450 degradation in microsomes?
Perform a carbon monoxide binding difference spectrum as published by XenoTech scientists.* If you see a large peak at 420 nm, it is likely that P450 has started to degrade to its inactive form of P420.
Caution: hemoglobin, often found in the microsomes as a contaminating protein, can give a peak at 420 nm also. Follow the Matsubara method described in the publication referenced below.
Alternatively, you can perform an enzyme assay and compare the rates you measure with those provided on the product datasheet.
*Pearce R, McIntyre CJ, Madan A, Sanzgiri U, Draper AJ, Bullock P, Cook DC, Burton LA, Latham J, Nevins C and Parkinson A
(1996) Effects of freezing, thawing, and storing human liver microsomes on cytochrome P450. Arch Biochem Biophys 331:145-169.
Why are the activities in your average pool of human liver microsomes generally higher than another commercially-available "high activity" pool?
We are confident that the activities in our pooled human liver microsomes reflect a true average range--not high activities.
Our acceptance criteria are calculated from our historical data, which represents the characterization of over 400 individual human livers to date. We select each of the 50 donors that comprise this pool and combine them to ensure that average activities are met for each of the enzymes, and that each donor is significantly represented in the pool.
All of our enzymatic assays are performed using LC/MS/MS validated methods, and all data are reviewed by our Quality Control staff prior to the product's release, so we are confident that the product you receive reflects average human activities.