Intracellular and extracellular phenoloxidases in the fungus Podospora anserina: Effect of a constitutive mutation in a gene involved in their posttranscriptional control

Summary

Three phenoloxidases- and in particular phenoloxidase B, an enzyme found in cell extracts only in the cases of protoplasmic incompatibility and cell lysis where it occurs in association with a protease — were investigated in a wild type strain. Phenoloxidase B was present only in the culture filtrates, while the other two phenoloxidases were found in cell extracts and in the culture medium. Addition of casaminoacids and ammonium acetate to the culture medium produced opposite effects: under the first conditions, phenoloxidase B increased in being present only in the culture filtrates and in the second medium, like a second phenoloxidase (activity C), phenoloxidase B completely disappeared from the culture filtrates.

A recessive mutation was isolated in a gene modB that resulted in the production of phenoloxidases B and C in higher amounts. The temperature dependence of the mutation modB allowed us to show that the formation of the phenoloxidases was 5 Fluorouracilresistant and cycloheximide sensitive, suggesting that constitutivity for these enzymes resulted from a derepression in their posttranscriptional control. Because of this derepression, phenoloxidase B not only increased in the culture medium (30x), but was found in cell extracts in association with a protease whose presence is suspected to produce a premature disintegration of the mycelium.

The results are discussed from the point of view of the processes capable of regulating the production of exoenzymes and in relationship with the phenomenon of cell death normally affecting mycelia during ageing.