Long chain fatty acid synthesis in developing castor bean seeds II. Operation of the path from sucrose to long chain fatty acids in a subcellular particulate system

Particles spun down at 10,000 ? g from developing castor beanseeds were capable of synthesizing LFAs from sucrose, a physiologicalprecursor transferred from leaves as a photosynthetic product.Tracer experiments, in combination with inhibitor effects, intermediatedilutions and cofactor requirements, indicated the operationof the following path: sucroseUDPGG-1-PG-6-PGAPpyruvateacetyl-CoAmalonyl-CoALFA.The whole path appears to be associated with 10,000 ? g particles,because repeated washings were unsuccessful in dissociatinga partial path from the particles, depsite of disorganizingthe structure of the particles. Based on the occurrence of freehexose(s) and the utilization of UDPG similar to that of sucroseor G-1-P in this reaction, it is probable that hexose phosphateis formed from sucrose via UDPG and fructose, although the conversionof sucrose to hexose phosphates via glucose and furctose isnot ruled out. Inhibitor experiments showed that ATP is self-supportingover the whole path, the ATP formed in the glycolytic path beingconsumed in a acetyl-CoA carboxylation step. Since oxidizedpyridine nucleotides are as available as reduced ones for LFAsynthesis, they seem to shuttle between the reduction in theconversion of sucrose to acetyl-CoA and the oxidation in LFAsynthesis from acetyl-CoA. From the pattern of the LFAs synthesized,NAD⁺ is available for the synthesis of saturated LFAs (18: 0,16: 0). whereas NADP⁺ is available for that of unsaturated LFAs(18: 1, 16: 1). (Received July 23, 1973; )