Maureen Bafor

Properties of the glycerol acylating enzymes in microsomal preparations from the developing seeds of safflower (Carthamus tinctorius) and turnip rape (Brassica campestris) and their ability to assemble cocoa-butter type fats

Microsomal membrane preparations from the developing seeds of safflower (Carthamus tinctorius, var. Gila) and turnip-rape (Brassica campestris, var. Bele) catalyzed the assembly of triacylglycerols (triglycerides) from sn-glycerol 3-phosphate and acyl-CoA. The membrane preparations were used to assess the acyl specificity properties of the initial acylating enzymes—glycerol 3-phosphate acyltransferase (GPAT) and 1-acylglycerol 3-phosphate acyltransferase (lysophosphatidic acid acyltransferase, LPAAT)—that are responsible for the fatty acids at positions sn-1 and sn-2 of the sn-triacylglycerol, respectively. In spectrophotometric assays it was possible to evaluate, to some extent, how these enzymes will utilize unusual and foreign fatty acids that are not normally found in these particular plant species. The acylating enzymes from both plants used, to varying extents, a comprehensive range of acyl-CoA donor species and some kinetic properties of the substrates involved are presented. The enzymes from safflower, however, were generally the more selective, whereas the turnip-rape was less particular and could utilize a range of acyl substrates. The enzymes from both plants hardly utilized erucate (C22∶1), and the significance of this is discussed in terms of mechanisms which have evolved in order to exclude certain, perhaps detrimental, fatty acids from structural membrane lipids and dedicate them to storage lipid assembly.The ability of the microsomal preparations, from the developing seeds of both plants, to synthesize cocoabutter type fats was investigated. Microsomal membranes were incubated with glycerol 3-phosphate and equimolar amounts of palmitate, oleate and stearate. Safflower preparations catalyzed the construction of sn-triacylglycerol with largely palmitate, oleate and stearate in positions sn-1, 2 and 3, respectively. The selectivity for acyl species in rape was less pronounced, however, substantial saturated-unsaturated-saturated oils were still produced. The results are discussed in terms of the acyl selectivity properties of the glycerol acylating enzymes. It is evident that given the correct composition of fatty acids, the plant can produce cocoabutter or other exotic fats.

Substrate specificities of glycerol acylating enzymes from developing embryos of two Cuphea species

Abstract Embryos of Cuphea procumbens accumulate triacylglycerols with nearly 90 mo1% of capric acid (10:0), whereas, C.wrightii embryos have 33% of 10:O and 54% of lauric acid (12:0) in their triacylglycerols. Acylation rates of different acyl substrates by microsomal glycerol 3-phosphate acyltransferases (GPAT, EC 2.3.1.15) and lysophosphatidic acid acyltransferases (LPAAT, EC 2.3.1.51), prepared from developing embryos of these species, were studied. Both types of enzymes differed in their acyl specificities between the two species. The GPAT and LPAAT from C. wrightii showed low activity with 10:0-CoA whereas this acyl-CoA was efficiently used for both acylation reactions by the C. procumbens enzymes. The LPAAT from C. wrightii showed relatively higher activities using acyl-CoA, with acyl chains longer than 10:0, than the corresponding enzyme from C. procumbens . With increasing chain length of the lysophosphatidic substrate increasingly longer acyl-CoA could serve as acyl donors in the LPAAT catalysed reaction from both species.

Medium chain-length fatty acids in lipids of developing oil palm kernel endosperm

Abstract The content and acyl qulity of triacylglycerol (TAG), diacylglycerol (DAG) and phosphatidylcholine (PC) in developing palm kernels ( Elaeis guineensis ) endosperm were determined between 8–20 weeks after anthesis (WAA). Rapid accumulation of TAG ( ca 65 μmol per kernel per week) started at 13 WAA and continued until 17 WAA. Accumulation of DAG followed a similar pattern to TAG but was two orders of magnitude less in quantity. The content of the major phospholipid, PC, was more or less constant from 8 to 17 WAA. The levels of medium chain-length fatty acids were very low in all lipid classes at 8 WAA. There was a rapid increase in the relative amounts of 12:0 and 14:0 in TAG between 8 and 12 WAA, after which their proportions remained fairly constant throughout kernel development. The content of 12:0 and 14:0 in PC and DAG increased up to 13 WAA, after which there was a substantial decrease. The decrease in the proportions of 12:0 and 14:0 in DAG and PC coincided with the onset of the rapid TAG synthesis. The results are discussed in terms of the regulation of oil biosynthesis in tissues accumulating medium chain-length fatty acids.

Biosynthesis of an Acetylenic Fatty Acid in Microsomal Preparations from Developing Seeds of Crepis Alpina

Over 600 naturally occuring compounds with acetylenic bonds (triple bonds) have been characterized (Bohlmann et al., 1973). Previous in-vivo studies, from mosses accumulating acetylenic fatty acids, indicate that the acetylenic bond is formed by the substraction of two hydrogen atoms from a double bond (Kohn et al., 1994).