Metabolism of 1-acyl-2-oleoyl-sn-glycero-3-phosphoethanolamine in castor oil biosynthesis.
We have examined the role of 2-oleoyl-PE (phosphatidylethanolamine) in the biosynthesis of triacylglycerols (TAG) by castor microsomes. In castor microsomal incubation, the label from 14C-oleate of 1-palmitoyl-2-[1-(14)C]oleoyl-sn-glycero-3-phosphoethanolamine is incorporated into TAG containing ricinoleate. The enzyme characteristics, such as optimal pH, and the effect of incubation components of the oleoyl-12-hydroxylase using 2-oleoyl-PE as incubation substrate are similar to those for 2-oleoyl-PC (phosphatidylcholine). However, compared to 2-oleoyl-PC, 2-oleoyl-PE is a less efficient incubation substrate of oleoyl-12-hydroxylase in castor microsomes. Unlike 2-oleoyl-PC, 2-oleoyl-PE is not hydroxylated to 2-ricinoleoyl-PE by oleoyl-12-hydroxylase and is not desaturated to 2-linoleoyl-PE by oleoyl-12-desaturase. We have demonstrated the conversion of 2-oleoyl-PE to 2-oleoyl-PC and vice versa. The incorporation of label from 2-[14C]oleoyl-PE into TAG occurs after its conversion to 2-oleoyl-PC, which can then be hydroxylated or desaturated. We detected neither PE-N-monomethyl nor PE-N,N-dimethyl, the intermediates from PE to PC by N-methylation. The conversion of 2-oleoyl-PE to 2-oleoyl-PC likely occurs via hydrolysis to 1,2-diacyl-sn-glycerol by phospholipase C and then by cholinephosphotransferase. This conversion does not appear to play a key role in driving ricinoleate into TAG.
Lin
J T
JT
U.S. Department of Agriculture, Agricultural Research Service, Western Regional Research Center, Albany, California 94710, USA. jtlin@pw.usda.gov
Lew
K M
KM
Chen
J M
JM
Iwasaki
Y
Y
McKeon
T A
TA
D002368:Castor Oil / Q000096:biosynthesis*; D002851:Chromatography, High Pressure Liquid; D004926:Escherichia coli / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006900:Hydroxylation; D008861:Microsomes / Q000378:metabolism*; D009829:Oleic Acids / Q000378:metabolism* / Q000502:physiology; D010713:Phosphatidylcholines / Q000378:metabolism* / Q000502:physiology*; D010714:Phosphatidylethanolamines / Q000378:metabolism* / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry; D012277:Ricinoleic Acids / Q000737:chemistry; D013303:Streptomyces antibioticus / Q000201:enzymology; D013997:Time Factors
D005227:Fatty Acids; D009829:Oleic Acids; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D011994:Recombinant Proteins; D012277:Ricinoleic Acids; D002368:Castor Oil; C005235:methyl ricinoleate