Fine structural localization of alkaloid synthesis in endoplasmic reticulum of submerged Claviceps purpurea

Acetyl coenzyme A (CoA) carboxylase (EC 6.4.1.2), an enzyme catalyzing the synthesis of malonyl-CoA, was cytochemically localized in endoplasmic reticulum (ER) of sclerotia-like cells of submerged Claviceps purpurea Tul. producing clavine alkaloids. The enzymic activity was structurally bound in unit membranes of ER strands which, later on, evolved into vacuoles containing lipoprotein material. The reaction product was absent from ER in nonvacuolized filamentous hyphae and ovoid asexual spores containing numerous lipid globules; it was also absent from ER in the mycelium of submerged C. purpurea strain producing no alkaloids. In view of our previous morphogenetic observations and the available biochemical evidence, the observed localization of acetyl-CoA carboxylase was assumed not to coincide with fatty acid biosynthesis but to represent sites of alkaloid synthesis.