The radiochemical assay for juvenile hormone biosynthesis in insects: problems and solutions

Measurement of juvenile hormone (JH) production using the radiochemical ass ay (RCA) for JH biosynthesis and release is usually a reliable and precise technique. However problems with radiolabeled precursors and misunderstandi ng of the data, the techniques and the calculations have contributed toward s uncertainty with respect to published experimental results. Problems with the purity of [methyl-H-3]-methionine or determination of its specific rad ioactivity have had detrimental effects on the reliability of results using the RCA. Proper control procedures and the use of C-14/H-3-double-label RC A can be useful in detecting irregularities in the experimental results, an d in determining contributing factors to any problems. The use of [methyl-C -14]-methionine and an awareness of normally expected RCA values can also a ssist the researcher in checking the validity of results. The radiolabeled methyl moiety of methionine is incorporated into JH without discrimination relative to unlabeled methyl methionine, by the o-methyl transferase. Howev er unexpected preferential incorporation of the [methyl-C-14]- vs. [methyl- H-3] -moiety into JH occurs, but is only evident at concentrations of radio labeled methionine outside the normal range of the RCA. Changes in radioact ive precursor formulation have no effect on the RCA. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.