A specific acyl-ACP thioesterase implicated in medium-chain fatty acid production in immature cotyledons of Umbellularia californica.
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.
Pollard
M R
MR
Calgene Inc., Davis, California 95616.
Anderson
L
L
Fan
C
C
Hawkins
D J
DJ
Davies
H M
HM
D003067:Coenzymes / Q000378:metabolism; D005227:Fatty Acids / Q000096:biosynthesis*; D006868:Hydrolysis; D007700:Kinetics; D010944:Plants / Q000201:enzymology / Q000378:metabolism*; D013379:Substrate Specificity; D013869:Thiolester Hydrolases / Q000378:metabolism*
D003067:Coenzymes; D005227:Fatty Acids; D013869:Thiolester Hydrolases; C018748:oleoyl-(acyl-carrier-protein) hydrolase