Abstract
Ethanolamine phosphotransferase (EPT) is a key enzyme responsible for the synthesis of ethanolamine glycerophospholipids. Plasmenylethanolamine is a predominant molecular subclass of ethanolamine glycerophospholipids in the heart. The present study was designed to identify the selective use of 1-O-alk-1'-enyl-2-acyl-sn-glycerol as a substrate for EPT as a mechanism responsible for the predominance of plasmenylethanolamine in the rabbit heart. EPT activity in rabbit myocardial membranes using 1,2-diacyl-sn-glycerol as substrate is activated by Mn2+, inhibited by dithiobisnitrobenzoic acid (DTNB) and is unaffected by Ca2+. In contrast, ethanolamine phosphotransferase activity using 1-O-alk-1'-enyl-2-acyl-sn-glycerol as substrate is inhibited by Mn2+ and Ca2+, but is activated by DTNB. Additionally, ethanolamine phosphotransferase activity using 1-O-alk-1'-enyl-2-acyl-sn-glycerol substrate was more sensitive to thermal denaturation compared with that of 1,2-diacyl-sn-glycerol. Taken together, these results suggest that separate ethanolamine phosphotransferase activities are present in heart membranes that are responsible for the synthesis of phosphatidylethanolamine and plasmenylethanolamine.
Highlights
Ethanolamine phosphotransferase (EPT) is a key enzyme responsible for the synthesis of ethanolamine glycerophospholipids
EPT activity was measured in Triton X-100 mixed micelles containing selected concentrations of diradylglycerols and rabbit myocardial membranes as the enzyme source
Reversed phase HPLC analysis of the products of the EPT assay in the presence of 5 mol% AAG and 5 mol% DAG confirmed that greater than 90% of the ethanolamine glycerophospholipid formed was plasmalogen
Summary
Ethanolamine phosphotransferase (EPT) is a key enzyme responsible for the synthesis of ethanolamine glycerophospholipids. The present study was designed to identify the selective use of 1-O-alk-1-enyl-2-acyl-sn-glycerol as a substrate for EPT as a mechanism responsible for the predominance of plasmenylethanolamine in the rabbit heart. Ethanolamine phosphotransferase activity using 1-O-alk-1-enyl-2-acyl-sn-glycerol substrate was more sensitive to thermal denaturation compared with that of 1,2-diacyl-sn-glycerol Taken together, these results suggest that separate ethanolamine phosphotransferase activities are present in heart membranes that are responsible for the synthesis of phosphatidylethanolamine and plasmenylethanolamine.—Ford, D. A second EPT activity has been identified that utilizes DAG as substrate, is sensitive to DTNB treatment, and is activated by Mn2ϩ Taken together, these are the first studies to suggest the presence of two EPT activities in heart membranes that are specific for the two major diradyl glycerol substrates produced in the heart, AAG and DAG
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