and can be more problematic with initial use. The important point is that the relative price of a given restriction enzyme(or isoschizomer) may not be the best barometer of its performance in a specific application or procedure. The enzyme with the highest price does not necessarily guarantee optimal performance; nor does the one with the lowest price consistently translate into the best valu Most commercial suppliers maintain a set of quality assurance standards that each product must pass in order to be approved for release. These standards are typically described in the supplier's product catalogs and detailed in the Certificate of Analysis. When planning to use an enzyme for the first time, it is important to review the corresponding quality control specifications and any usage notes regarding recommended conditions and applications. What Can You Do to Reduce the Cost of working with Restriction Enzymes? Most common restriction enzymes are relatively inexpensiv and often maintain full activity past the designated expiration date. Restriction enzymes of high purity are often stable for many years when stored at -20C. In order to maximize the shelf life of less stable enzymes, many laboratories utilize insulated storage containers to mitigate the effects of freezer temperature fluctua tions. Periodic summary titration of outdated enzymes for activ ity is another way to reduce costs for these reagents. For most applications, 1 ul is used to digest 250ng to l ug of DNA. Enzymes supplied in higher concentrations may be diluted prior to the reac tion in the appropriate storage buffer. A final dilution range of 2000 to 5000 Umits/ml is recommended. However, reducing the amount of enzyme added to the reaction may increase the risk of incomplete digestion with insignificant savings in cost. Dilution is a more practical option when using very expensive enzymes, when sample DNA concentration is below 250ng per reaction, or when partial digestion is required. When planning for partial digestion erial dilution(discussed below) is recommended. Most diluted enzymes should be stable for long periods of time when stored at 20%C. as a rule it is wise to estimate the amount of diluted enzyme required over the next week and prepare the dilution he appropriate storage buffer, accordingly. For immediate use, most restriction enzymes can be diluted in the reaction buffer, kept on ice, and used for the day. Extending the reaction time to greater than one hour can often be used to save enzyme or ensure complete digestion Robinson et aland can be more problematic with initial use. The important point is that the relative price of a given restriction enzyme (or isoschizomer) may not be the best barometer of its performance in a specific application or procedure.The enzyme with the highest price does not necessarily guarantee optimal performance; nor does the one with the lowest price consistently translate into the best value. Most commercial suppliers maintain a set of quality assurance standards that each product must pass in order to be approved for release.These standards are typically described in the supplier’s product catalogs and detailed in the Certificate of Analysis. When planning to use an enzyme for the first time, it is important to review the corresponding quality control specifications and any usage notes regarding recommended conditions and applications. What Can You Do to Reduce the Cost of Working with Restriction Enzymes? Most common restriction enzymes are relatively inexpensive and often maintain full activity past the designated expiration date. Restriction enzymes of high purity are often stable for many years when stored at -20°C. In order to maximize the shelf life of less stable enzymes, many laboratories utilize insulated storage containers to mitigate the effects of freezer temperature fluctua￾tions. Periodic summary titration of outdated enzymes for activ￾ity is another way to reduce costs for these reagents. For most applications, 1ml is used to digest 250 ng to 1mg of DNA. Enzymes supplied in higher concentrations may be diluted prior to the reac￾tion in the appropriate storage buffer. A final dilution range of 2000 to 5000 Umits/ml is recommended. However, reducing the amount of enzyme added to the reaction may increase the risk of incomplete digestion with insignificant savings in cost. Dilution is a more practical option when using very expensive enzymes, when sample DNA concentration is below 250 ng per reaction, or when partial digestion is required. When planning for partial digestion, serial dilution (discussed below) is recommended. Most diluted enzymes should be stable for long periods of time when stored at -20°C. As a rule it is wise to estimate the amount of diluted enzyme required over the next week and prepare the dilution in the appropriate storage buffer, accordingly. For immediate use, most restriction enzymes can be diluted in the reaction buffer, kept on ice, and used for the day. Extending the reaction time to greater than one hour can often be used to save enzyme or ensure complete digestion. 228 Robinson et al