Thymidylate synthase activity from chlamydomonas cells and cultured tissues of Nicotiana, pinus, and daucus.

Prior preparation of N(5),N(10)-methylenetetrahydrofolate from dl-tetrahydrofolate and [(14)C]formaldehyde resulted in an improved assay for thymidylate synthase. Although preparations from tobacco seedlings and cotton root tips (0.25 centimeter) were inconsistent with respect to enzyme activity, extracts from actively growing cell cultures of Chlamydomonas, Nicotiana hybrid callus, Pinus callus, and Daucus proembryonic cells contained significant levels of thymidylate synthase (12.3 to 23.8 nanomoles of thymidylate formed per milligram of protein per hour).