BIOSYNTHESIS AND METABOLISM OF JUVENILE HORMONES

摘要

Juvenile hormone 111 biosynthesis starts with two molecules of acetyl-CoA condensing to form acetoacetyl-CoA which in turn combines with another molecule of acetyl-CoA to form 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). This compound is reduced to mevalonic acid which is phosphorylated and decarboxylated to form the 5 carbon isoprene unit, isopentenyl pyrophosphate (IPP) which isomerizes to form dimethylallyl pyrophosphate (DMAPP). DMAPP combines with IPP to form geranyl pyrophosphate which in turn combines with IPP to form farnesyl pyrophosphate. This compound is oxidized stepwise to farnesol, farnesal and finally farnesoic acid. This acid is esterified with a methyl group and epoxidized at the other end to form JH 111. Juvenile hormone 0 exemplifies the alternate pathway which starts with propionyl-CoA which condenses with acetyl-CoA to form the 5 carbon, 3-ketovaleryl-CoA instead of acetoacetyl-CoA. This compound combines with acetyl-CoA to form the 7 carbon, 3-hydroxy-3-ethylglutaryl-CoA which is then reduced to homomevalonate. This material is phosphorylated and decarboxylated to form homoisopentenyl pyrophosphate (HIPP) which isomerizes to form ethylmethylallyl pyrophosphate (EMAPP). The extra carbon necessary for ethyl substitution is generated by EMAPP. EMAPP combines with 2 molecules of HIPP in sequence followed by oxidation to the acid, methyl esterification and epoxidation resulting in the formation of JH-O. JH 11, JH 1 and 4-methyl JH 1 have both methyl and ethyl substituents which can be handled by using both 5 and 6 carbon units to obtain the appropriate substitution. JH 11 for instance starts off with EMAPP combining with IPP twice to get the right structure. JH 1 starts with EMAPP combining with HIPP followed by IPP. 4 methyl JH 1 starts with EMAPP combining with HIPP then combines with HIPP which has the double bond in the 3-4 position to enable the methyl substitution at the C-4 position.