Partial purification and photoaffinity labelling of sunflower acyl-CoA: lysophosphatidylcholine acyltransferase

Previous attempts to purify acyl-CoA:1-acyl-lyso-phosphatidylcholine acyltr ansferase (EC 2.3.1.23) have been frustrated by difficulties in solubilizin g the enzyme without inactivation. Microsomal preparations, from the develo ping cotyledons of sunflower, in high concentrations of urea retain activit y. Gel-filtration liquid chromatography followed by trypsin treatment (minu s urea) resulted in the removal of many contaminating proteins without loss of enzyme activity. SDS/PAGE showed the presence of two major peptides wit h apparent molecular masses of 52 and 59 kDa. These polypeptides cross-reac ted with the radio-labelled photoreactive substrate 1-azido-oleoyl-sn-lysop hosphatidyl- [N-methyl-H-3] choline.