The determination of enzyme levels in cellular extracts by active site titrations or by catalytic activity measurements is relevant in both science and medicine. However, these techniques assume that enzymes exhibit the same response in crude sample matrices as they do in the purified state. We report here an example of how an enzyme-linked immunosorbent assay (ELISA) was used to determine the true enzyme concentration which was compared to the effective enzyme concentration obtained by ligand binding and catalytic assay methods in a crude bacterial cell extract. Rabbit antibodies specific for Lactobacillus casei thymidylate synthase (TS) were used to develop a highly specific and sensitive heterogeneous noncompetitive ELISA assay with a typical detection limit of 1.4 fmol of TS (100 pg) and a dynamic working range of 3 orders of magnitude. The antibodies showed identical responses for TS, its inhibitory binary complex with 5-fluoro-2'-deoxyuridylate, and its inhibitory ternary complex with 5-fluoro-2'-deoxyuridylate and 5,10-methylenetetrahydrofolate in the immunoassay. L. casei cell-free extracts were subjected to extraction with CM-Sephadex and the various fractions were analyzed by ELISA, active-site titrations, and catalytic assays which demonstrated that assays which assumed full catalytic or ligand-binding competence underestimated the true enzyme level.

Blotting, Western↗

PubMedDate not supplied

Family planning communications and contraceptive use in Guatemala, El Salvador, and Panama.

Recent contraceptive prevalence surveys in Guatemala, El Salvador, and panama included a module on family planning communications. This module provided useful feedback on the reach of each program and facilitated comparisons between countries. While almost all women in El Salvador have been reached by family planning messages, the percentage of women reached was lower in Panama and Guatemala. In all three countries rural, less educated, and unemployed women who worked inside the home or not at all were least likely to have seen or heard the messages. Exposure to family planning communications emerged as a strong correlate of contraceptive use, as shown in two separate analyses. These findings underscore the importance of communications in promoting contraceptive use.

Communication↗