Enzyme Unit Activity Comparison Chart

       Enzyme units vary and the differences can make comparing products from different sources difficult. Unit definitions may appear to be identical however one cannot assume that the potency of a unit is the same between suppliers. Using a common assay procedure, Life Sciences Advanced Technologies has tested AMV RT in our laboratories from the below suppliers. As you can see, there is much deviation between claimed u/µL and actual assay value u/µL. Life Sciences Advanced Technologies by far maintains the closest ratio between claimed units and assay value.  
     
Supplier Claimed U/μL Assayed Value U/μL Deviation Suppliers Unit Definition  
LSAT 14.6 14.1 3% 1 Unit = amount required to incorporate 1 nmol of TTP into acid-insoluble material in 10 min. at 37ºC
Gene Choice 10 5.7 43% 1 Unit = amount required to incorporate 1 nmol dTTP into acid precipitable material in 10 min. at 37ºC
Invitrogen (cloned) 15 13 12% 1 Unit = amount required to incorporate 1 nmol dTTP into acid-precipitable material in 10 min. at 37ºC, using polyA:oligo (dT)25 as a primer
New England Biolabs 25 4.1 83% 1 Unit = amount required to incorporate 1 nmol dTMP into acid-insoluble form in 10 min. at 37ºC using Poly A: oligo (dT) as template primer
Promega 24 4.6 81% 1 Unit = amount required to incorporate 1 nmol deoxynucleotide into acid-precipitable material in 10 min. at 37ºC
Seikagaku 26 9.7 62% 1 Unit = amount required to incorporate 1 nmol dTMP into acid-insoluble material in 10 min. at 37ºC
USB (Affymetrix) 15 3 80% 1 Unit = amount required to incorporate 1 nmol TMP into acid-insoluble material in 10 min. at 37ºC
 
 
      Claimed U/µL: the Unit concentration from the supplier’s product labeling.
Assay Value U/µL: the average of 2 assays (4 for LSAT).
Deviation: expressed as the percentage deviation from the value claimed by the supplier against the LSAT result. LSAT Assay conditions: 4.0mM DTT, 50mM Tris-HCI (pH 8.3), 40mM KCI, 6mM MgCI2, 0.4mM r(A)n(dT)12-18, 0.5mM (3H)-TTP, AMV RT’s diluted with 0.O1M phosphate buffer (pH 7.2), 2mM DTT, 10% glycerol, 0.2% Triton x 100.		  
      Conclusion:Life Sciences Advanced Technologies maintains the closest ratio between claimed units and assay value.If you use significant amounts of an enzyme, it is worth your time to assay different suppliers’ products to ensure a meaningful comparison and good value.