Precursor supply for insect juvenile hormone III biosynthesis in a cockroach

The biosynthesis of the sesquiterpenoid juvenile hormone III (JH III) was studied using corpora allata of the cockroach Diploptera punctata incubated in vitro and a radiochemical assay for the hormone produced. The influence of several exogenous precursors such as glucose, trehalose, acetate, amino acids, and mevalonate on JH synthetic rates was studied. Glucose or trehalose were needed for an optimal rate of JH synthesis. Highest rates were achieved at trehalose concentrations below the normal hemolymph levels (35-40 mM). About one-third of the glucose utilized for the biosynthesis of JH III was metabolized through a pentose pathway, but acetyl-CoA derived from glucose was significantly diluted by acetyl-CoA from other sources. Amino acids provided both a source of carbon for JH III synthesis and a source of energy that allowed JH III synthesis from acetate and stimulated JH III synthesis from glucose. Acetate was a poor substrate, because it could not support JH III synthesis in long term incubations. The incorporation of exogenous mevalonate into JH III was dependent on the physiological state of the glands, but there was a significant dilution with endogenous mevalonate. This dilution reflected in part the poor penetration of mevalonate into the corpora allata cells, because JH synthesis in mevinolin-treated cells was not fully rescued by mevalonate.