COMPARISON OF CERTAIN PROPERTIES OF MEMBRANE-BOUND AND SOLUBILIZED ACYLTRANSFERASE ACTIVITIES OF PLANT MICROSOMES

Solubilized microsomal sn-glycerol-3-phosphate acyltransferase fractions were prepared by extracting membrane fractions from spinach leaves and etiolated pea seedlings with Tween 40 in the presence of NaCl. A comparison of the properties of the membrane bound n-glycerol-3-phosphate acyltransferase and of the solubilized activity revealed that both enzymic forms displayed very similar fatty acid specificities and selectivities but different positional specificities. While the membrane bound enzyme directed the acyl groups to the C-1 position of sn-glycerol-3-phosphate, the solubilized form catalyzed the acylation at the C-2 position. Moreover, in the microsomal fractions solubilized with Tween 40 a 2-acyl-sn-glycerol-3-phospate AT was detectable, which showed a pronounced selectivity for palmitoyl groups. On the other hand, when the microsomal membranes were extracted with Tween 80 instead of Tween 40, the sn-glycerol-3-phosphate acyltransferase of the resulting solubilized fractions displayed the same positional specificity as in the microsomal fractions. These results indicate that in contrast to the experiments with Tween 40, in which presumably latent activities were induced, the extraction of microsomal membranes with Tween 80 resulted in the solubilization of at least part of the native sn-glycerol-3-phosphate acyltransferase. © 1990.