Extracts of dichloromethotrexate-resistant Lactobacillis casei provide a rich source of stable
thymidylate synthetase, showing 100 times the activity found in extracts of the sensitive
strain. The enzyme was purified 17-fold from extracts of resistant cells. It has a molecular
weight of 67,000 and is activated by 2-mercaptoethanol. The rate of the reaction as
determined by loss of tritium from deoxyuridine monophosphate-5-3 H was 84% of the rate
observed spectrophotometrically. The enzyme from dichloromethotrexate-resistant L. casei …

Extracts of dichloromethotrexate-resistant Lacfobucillis casei provide a rich source of stable
thymidylate synthetase, showing 100 times the activity found in extracts of the sensitive
strain. The enzyme was purified 17-fold from extracts of resistant cells. It has a molecular
weight of 67,000 and is activated by Z-mercaptoethanol. The rate of the reaction as
determined by loss of tritimn from deoxyuridine monophosphate-5-3H was 84% of the rate
observed spectrophotometrically. The enzyme from dichloromethotrexate-resistant L. casei …