Lysophosphatidate Acyltransferase Activities in the Microsomes from Palm Endosperm, Maize Scutellum, and Rapeseed Cotyledon of Maturing Seeds

Abstract

Lysophosphatidate (LPA) acyltransferase (EC 2.3.1.51) in the microsomes from palm endosperm (Syagrus cocoides Martius), maize scutellum (Zea mays L.), and rapeseed cotyledon (Brassica napus L.) of maturing seeds were studied for their specificities toward the acyl moiety of the substrates lysophosphatidate and acyl coenzyme A (CoA). The LPA acceptor greatly influenced the acyl CoA specificity of the enzyme and vice versa. With 1-oleoyllysophosphatidate (LPA-18:1), the palm enzyme was equally active on oleoyl CoA and lauroyl CoA, whereas the maize and rapeseed enzymes were more active on oleoyl CoA than on lauroyl CoA. With 1-lauroyl-lysophosphatidate (LPA-12), which generated less activity than LPA-18:1, the palm enzyme was three times more active on lauroyl CoA than on oleoyl CoA. LPA-12 was an inactive substrate for the maize and rapeseed enzymes. The selectivity of the enzymes was also studied using a mixture of LPA-18:1 and LPA-12, as well as lauroyl CoA and oleoyl CoA. Under this selectivity condition and compared to the specificity condition, the enzymes from all the three seeds exerted stronger preference for oleoyl moiety in either the LPA or acyl CoA, and again, only the palm enzyme could act on LPA-12.Similar studies, although in lesser detail, showed that the enzymes from soybean and castor bean were similar to the maize and rapeseed enzymes in having little activity on substrates containing lauroyl moiety. The results demonstrate the importance of the acyl group in the sn-I position of LPA in determining the acyl preference in the sn-2 position in phosphatidate synthesis. The palm enzyme appears to be the only one capable of synthesizing phosphatidates containing high amounts of lauric moieties.In oil seeds, TAG3 synthesis proceeds via the Kennedy pathway (20). Glycerol-3-P is first acylated by glycerol-3-P AT at the sn-l position to form lysophosphatidate, which undergoes a second acylation by LPA-AT to form phosphatidate.

Lysophosphatidate Acyltransferase in the Microsomes from Maturing Seeds of Meadowfoam (Limnanthes alba)

“…Specifically, we have been studying the enzymes from different oilseed species to see if they can use short (lauric) and long (erucic)-chain acyl moieties in the substrates. In the study of LPA-AT in using substrates containing lauroyl moiety, we have found that the enzyme from palm kernel can use LPA-lauroyl and lauroyl CoA as the substrates, whereas those from other oilseed crops containing the normal C-16 and C-18 acyl moieties in seed TAG are unable to do so (10,15). This finding is consistent with the presence of lauroyl moiety in the sn-2 position of palm kernel Plant Physiol.…”

“…We chose to study the substrate specificity (supplying one acyl acceptor and one acyl donor) rather than the substrate selectivity (supplying a mixture oftwo acyl acceptors and one acyl donor, and vice versa). The test ofspecificity is less stringent than the test ofselectivity in detecting substrate preference, as shown in the studies of LPA-AT from palm (10) and meadowfoam (to be described), and thus facilitates the detection of LPA-AT that can use substrates containing erucoyl moieties.…”

“…In view of the importance of LPA-AT in controlling the acyl moities in seed TAG, we have been studying this enzyme from various oilseed species (10,15). We have made direct comparisons of the enzymes from various species in order to understand the flexibility and limitation of their acyl preference which controls the acyl moiety in the sn-2 of seed TAG.…”

Ubiquitous and Endoplasmic Reticulum–Located Lysophosphatidyl Acyltransferase, LPAT2, Is Essential for Female but Not Male Gametophyte Development in Arabidopsis

“…coconut and meadowfoam microsomal LPATs. This last group might represent seed-specific LPATs that can acylate a unique acyl group to the sn-2 position of a TAG molecule (Kim and Huang, 2004), such as C-12 in coconut (Oo and Huang, 1989;Knutzon et al, 1995) and C-22:1 in meadowfoam (Cao et al, 1990;Hanke et al, 1995). Nevertheless, this last group also includes a rice LPAT derived from a genomic sequence, and rice seed TAG is not known to possess a unique acyl moiety at the sn-2 position.…”

Metabolic Interactions between the Lands Cycle and the Kennedy Pathway of Glycerolipid Synthesis in Arabidopsis Developing Seeds

“…A fascinating aspect of glycerolipid biosynthesis is that there often exists an asymmetric distribution of fatty acid (FA) molecules between the sn-1 and sn-2 positions: Saturated and monounsaturated FAs are normally found at sn-1, whereas polyunsaturated fatty acids (PUFAs) are enriched at sn-2. Pioneering work on plant acyltransferases has shown that GPATs and LPAATs are not only stereo-specific with regard to acylation of the glycerol backbone but also selective in terms of acyl-CoA donors (Griffiths et al, 1985;Ohlrogge and Browse, 1995;Oo and Huang, 1989;Bourgis et al, 1999;Kim and Huang, 2004;Kim et al, 2005). Therefore, the substrate specificity of the acyltransferases of the Kennedy pathway is one of the determining factors of the composition of glycerolipid molecules.…”