SUBCELLULAR LOCATION OF THE DELTA(12) DESATURASE RULES OUT BACTERIOCYTE CONTRIBUTION TO LINOLEATE BIOSYNTHESIS IN THE HOUSE CRICKET AND THE AMERICAN COCKROACH

Subcellular membranes from cricket whole-body homogenates and cockroach fat body homogenates were separated by differential and isopycnic centrifugation. Marker enzymes, phosphatidylcholine glyceride transferase, Na+/K+-ATPase and H+-ATPase, were assayed to establish the identity of the endoplasmic reticulum, plasma membrane and mitochondria, respectively. Electron microscopy of the separate membrane fractions revealed distinct morphological differences in each fraction. The DELTA12 desaturase activity was found to comigrate with the lightest fraction, the endoplasmic reticulum, while the endosymbiotic bacteria were recovered in the cell debris and mitochondrial fractions. These results provide definitive evidence that the DELTA12 desaturase activity in Acheta domesticus and Periplaneta americana is of insect origin and not due to endosymbiotic bacteria. This is also the first reported separation of a microsomal fraction from insects into endoplasmic reticulum and plasma membranes.