A specific acyl-ACP thioesterase implicated in medium-chain fatty acid production in immature cotyledons of Umbellularia californica

Arch Biochem Biophys. 1991 Feb 1;284(2):306-12. doi: 10.1016/0003-9861(91)90300-8.


Umbellularia californica (California Bay) seeds accumulate 10:0 and 12:0 as principal reserve fatty acyl groups. An in vitro fatty acid synthesis system from the developing cotyledons produces chiefly 10:0 and 12:0, in approximately the same proportions as the intact tissue. The kinetics of acyl thioester and free fatty acid formation in this system suggest that a medium-chain specific acyl-acyl-carrier protein (ACP) hydrolysis mechanism is responsible for the preponderance of medium-chain products. A crude extract of the developing cotyledons exhibits hydrolytic activity toward acyl-ACPs, with marked preference for 12:0-ACP and 18:1-ACP in the test series 6:0, 8:0, 10:0, 11:0, 12:0, 14:0, 16:0, and 18:1-ACPs. Partial purification of the 12:0-ACP hydrolytic activity has resulted in its separation from the 18:1-ACP hydrolase(s) and the 12:0-coenzyme A hydrolase(s) that are also present, thereby demonstrating its specificity for the 12-carbon acyl chain length and the ACP derivative. During cotyledon development, as the proportion of medium-chain to other fatty acyl groups increases, the extractable yield of this activity also increases substantially. Collectively these results suggest a role for this 12-ACP thioesterase in medium-chain production in vivo.

MeSH terms

  • Coenzymes / metabolism
  • Fatty Acids / biosynthesis*
  • Hydrolysis
  • Kinetics
  • Plants / enzymology
  • Plants / metabolism*
  • Substrate Specificity
  • Thiolester Hydrolases / metabolism*


  • Coenzymes
  • Fatty Acids
  • Thiolester Hydrolases
  • oleoyl-(acyl-carrier-protein) hydrolase