Palmitoyl acyl carrier protein

The thioesterase activity of the fatty acid synthase prefers the palmitoyl acyl carrier protein thioester as substrate. 

Jones, A., Davies, H.M., Voelker, T.A. 1995. Palmitoyl-acyl carrier protein (ACP) thioesterase and the evolutionary origin of plant acyl-ACP thioesterases. Plant Cell 7 359-371. 

Gaboon EB, Cranmer AM, Shanklin J, Ohhogge JB. (1994) Delta 6 hexadecenoic acid is synthesized by the activity of a soluble delta 6 palmitoyl-acyl carrier protein desaturase in Thunbergia alata endosperm. 7 Biol Chem 269 27519-27526. 

Gaboon, E Ohlrogge, J. Metabolic evidence for the involvement of a A4-palmitoyl-acyl carrier protein desaturase in petroselinic acid synthesis in coriander endosperm and transgenic tobacco cells. Plant Physiol, 1994, 104, 827-837. 

Bernerth, R. and Frentzen, M. 1990. Utilization of erucoyl-CoA by acyltransferases from developing seeds of Brassica napus L. involved in triacylglycerol biosynthesis. Plant Sci. 67 21-28. Bondaruk, M., Johnson, S., Degafii, A., Boora, R, Bilodeau, P., Morris, J., Wiehler, W., Foroud N., Weselake, R. and Shah S. 2007. Expression of a cDNA encoding palmitoyl-acyl carrier protein desaturase from cat s claw (Doxantha unguis-cati L.) in Arabidopsis thaliana and Brassica napus leads to accumulation of unusual unsaturated fatty acids and increased stearic acid content in the seed oil. Plant Breed. 126 186-194. 

Bhore, S.J., Shah, F.H., 2012. Genetic transformation of the American oil palm (Elaeis oleiferd) immature zygotic embryos with antisense Palmitoyl-acyl carrier protein thioesterase (PATE) gene. World Appl. Sci. J. 16 (3), 362-369. 

FIGURE 25.20 Triacylglycerols are formed primarily by the action of acyltransferases on mono- and diacylglycerol. Acyltransferase in E. coli is an integral membrane protein (83 kD) and can utilize either fatty acyl-CoAs or acylated acyl carrier proteins as substrates. It shows a particular preference for palmitoyl groups. Eukaryotic acyltransferases nse only fatty acyl-CoA molecnles as substrates. 

This enzyme, officially known as 3-hydroxypalmitoyl-[acyl-carrier protein] dehydratase [EC 4.2.1.61], is the fatty-acid synthase component that catalyzes the conversion of (3 i )-3-hydroxypalmitoyl-[acyl-carrier protein] to form 2-hexadecenoyl-[acyl-carrier protein] and water. This enzyme displays specificity toward 3-hydroxyacyl-[acyl-carrier protein] derivatives (with chain lengths from Ci2 to Cie), with highest activity on the palmitoyl derivative. See also Fatty Acid Synthetase... 

Suh et al. (1999) studied the isoforms of acyl carrier protein involved in seed-specific fatty acid synthesis in coriander seed, ft produces unusual monoenoic fatty acids which constitute over 80% of the total fatty acids of the seed oil. The initial step in the formation of these fatty acids is the desaturation of palmitoyl-ACP (acyl carrier protein) at the DELTA4 or DELTA6 positions to produce DELTA4-hexadecenoic acid (16 1DELTA4) or DELTA6-hexadecenoic acid (16 1DELTA6), respectively. 

Fig. 3. Generic reaction sequence for the FASs. ACP, acyl carrier protein AT, acetyltransferase MT, malonyl transferase KS, P-ketoacyl synthase KR, P-ketoacyl reductase DH, dehydrase ER, enoyl reductase TE, thioesterase FT, palmitoyl transferase. In the animal FAS the acetyl and malonyl loading reactions are catalyzed by the same acyl transferase and the chain-termination reaction is catalyzed by a thioesterase. In the fungal FAS, the malonyl loading and palmitoyl unloading reactions are catalyzed by the same acyl transferase. Stereochemical analyses in the laboratories of Comforth and Hammes established that in both animal and fungal FASs the KS-catalyzed condensation reaction proceeds with inversion of configuration at the malonyl C2 position, followed by KR-catalyzed reduction of the 3-keto moiety to the 3R alcohol by transfer of the pro-4S hydride from NADPH, and DH-catalyzed dehydration to a trans-enoyl moiety by the syn elimination of the 2S hydrogen and the 3/f hydroxyl as water. However, the stereochemistry of the final reduction reaction catalyzed by ER domain proceeds with different stereochemistry. The animal FAS transfers the pro-4R hydride of NADPH to the pro-3/f position with simultaneous addition of a solvent proton to the pro-2S position, whereas the fungal FAS takes the pro-4S hydride of NADPH into the pro-3S position and the solvent proton is incorporated at the pro-25 position.

There is increasing evidence that in plant tissues the synthesis of palmitic acid, the most abundant and important saturated fatty acid in higher plants, involves at/e novo system, so called because it utilizes acetyl-CoA, malonyl-CoA, acyl carrier protein (ACP), and a battery of soluble, nonassociated enzymes (palmitoyl-ACP synthetase) to form, as its terminal product, palmi-toyl-ACP. Palmitoyl-ACP is then elongated by another set of enzymes called... 

Figure 3.7 Model of intermolecular fatty acid synthetase mechanism in the a2 2 protomer of yeast. A, acetyl transferase E, enoyl reductase D, dehydratase P, palmitoyl transferase M, malonyl transferase C, 5-ketoacyl synthase R. )5-ketoacyl reductase ACP, acyl carrier protein. Dotted lines and arrows delineate the route taken by intermediates when sequentially processed on different FAS domains. Numbers indicate the reaction sequence. Catalytically active dohnains, at a specific moment, are marked by bold lines. Shaded areas on E and P domains potentially interact by hydrophobic attraction in the presence of palmitate (b). On the protomer depicted in (a) fatty acyl chain elongation occurs in one half of the a2 2 protomer. In (b) chain termination is induced by hydrophobic interaction between E> bound palmitate and P. Subsequently, palmitate Is transferred to Its O-ester binding site on P. Inactivation of the left half of simultaneously activates its right half (b). Redrawn from Schweizer (1984) with permission of the author and Elsevier Science Publishers, BV. From Fatty Acid Metabolism and its Regulation (1984) (ed. S. Numa), p. 73, Figure 7.

Figure 7.11 Mechanism of transport of long-chain fatty adds across the inner mitochondrial membrane as fatty acyl carnitine. CRT is the abbreviation for carnitine palmitoyl transferase. CPT-I resides on the outer surface of the inner membrane, whereas CPT-II resides on the inner side of the inner membrane of the mitochondria. Transport across the inner membrane is achieved by a carrier protein known as a translocase. FACN - fatty acyl carnitine, CN - carnitine. Despite the name, CRT reacts with long-chain fatty acids other than palmitate. CN is transported out of the mitochondria by the same translocase.

---