Identification and characterization of alkenyl hydrolase (lysoplasmalogenase) in microsomes and identification of a plasmalogen-active phospholipase A(2) in cytosol of small intestinal epithelium

A lysoplasmalogenase (EC 3.3.2.2; EC 3.3.2.5) that liberates free aldehyde from 1-alk-1'-enyl-sil-glycero-3-phosphoethanolamine or -choline (lysoplasm alogen) was identified and characterized in rat gastrointestinal tract epit helial cells. Glycerophosphoethanolamine was produced in the reaction in eq uimolar amounts with the free aldehyde. The microsomal membrane associated enzyme was present throughout the length of the small intestines, with the highest activity in the jejunum and proximal ileum. The rate of alkenyl eth er bond hydrolysis was dependent on the concentrations of microsomal protei n and substrate, and was linear with respect to time. The enzyme hydrolyzed both ethanolamine- and choline-lysoplasmalogens with similar affinities; t he ii;,, values were 40 and 66 mu M, respectively. The enzyme had no activi ty with 1-alk-1'-enyl-2-acyl-sn-glycero-3-phospor-choline (intact plasmalog en), thus indicating enzyme specificity for a free hydroxyl group at the sn -2 position. The specific activities were 70 nmol/min/mg protein and 57 nmo l/min/mg protein, respectively, for ethanolamine- and choline-lysoplasmalog en. The pH optimum was between 6.8 and 7.4. The enzyme required no known co factors and was not affected by low mM levels of Ca2+, Mg2+, EDTA, or EGTA. The detergents, Triton X-100, deoxycholate, and octyl glucoside inhibited the enzyme. The chemical and physical properties of the lysoplasmalogenase were very similar to those of the enzyme in liver and brain microsomes. III developmental studies the specific activities of the small intestinal and liver enzymes increased markedly, 11.1- and 3.4-fold, respectively, in the first similar to 40 days of postnatal life. A plasmalogen-active phospholip ase A? activity was identified in the cytosol of the small intestines (3.3 nmol/min/mg protein) and liver (0.3 nmol/min/mg protein) using a novel coup led enzyme assay with microsomal lysoplasmalogenase as the coupling enzyme. (C) 1999 Elsevier Science B,V. All lights reserved.