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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
Author(s) -
Bafor Maureen,
Stobart Allan Keith,
Stymne Sten
Publication year - 1990
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/bf02540647
Subject(s) - carthamus , acyltransferase , brassica , biochemistry , enzyme , acyltransferases , glycerol , microsome , fatty acid , biology , chemistry , botany , biosynthesis , medicine , traditional medicine
Abstract 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.