Localization of alkaline phosphatase activity at microbody membranes of Neurospora crassa and Aspergillus nidulans.

Hyphal cells of Neurospora crassa and Aspergillus nidulans, grown in Sabouraud glucose broth or in a defined medium with xanthine or its catabolites as the nitrogen source, contained single membrane-bound organelles cytochemically identified as microbodies. Modified Gomori procedures at the ultrastructural level revealed putative alkaline phosphatase activity sites in thin sections of cells of both species of fungi. Microbody membranes displayed electron opaque deposits (lead phosphate) which were absent in control preparations either lacking the substrate (beta-glycerophosphate) or the lead capture ion. Inhibition of this enzymic activity was achieved in parallel incubations fortified with the inhibitor levamisole. Cells grown in media containing limiting levels of inorganic phosphate revealed additional alkaline phosphatase activity at and along the nuclear membrane and endoplasmic cisternae. Hexagonal inclusions found in the cytoplasm of N. crassa (but not A. nidulans) and believed to arise from microbody precursors were without demonstrable cytochemical staining for microbody marker oxidases.