Insect cuticle is a first barrier againts chemical or biological insecticide penetration. Entomopathogenic fungi are able to use the cuticular hydrocarbons of their insect host as the sole carbon source for growth. Preliminary evidences in Beauveria bassiana indicate that the degradation pathway would be iniciated by terminal oxidation of the alkane by means of a microsomal cytochrome P-450 monooxigenase system, as determined by NADPH consumption measured spectrophotometrically in the presence of hydrocarbon substrates. The oxidation products are further degraded by b-oxidation steps providing the acetyl-CoA units needed for lipid synthesis, and releasing also acetic acid and CO2 (Mycologia 92: 528-536, 2000). Peroxisomes are the site of b-oxidation reactions in fungi, catalase (a typical peroxisomal marker) is an inducible enzyme participating in the final stages of hydrocarbon degradation.We detected catalase activity in the peroxisomal (pellet 20.000g) and cytosolic (supernatant 100.000g) fractions measuring H2O2 consumption at 240 nm by spectrophotometry. Induction of peroxisomal specific activity in alkane-grown strains produced a 2-fold increase as compared to that of control strains. Initial studies were perfomed with the cytosolic enzyme, after purification and characterization by native and SDS-PAGE, a molecular weight of 360 kDa was estimated for the tetrameric form.
