The mechanism of fungistatic action of sec-butylamine: I. Effects of sec-butylamine on the metabolism of hyphae of Penicillium digitatum

Growth of Penicillium digitatum was inhibited after a 40-min incubation in a culture medium containing 0.5 mM sec-butylamine, and the dry weight of the hyphae was 50% of the control value after 180 min. Respiration of the hyphae was reduced 13% after a 20-min contact with 0.5 mM sec-butylamine but this treatment did not influence the uptake of amino acids, glucose, or phosphate nor intensify the efflux of ³³P- or ¹⁴C-labeled metabolites from the cells. The syntheses of cell walls and total lipids were inhibited 20–30% after a 90-min incubation with sec-butylamine, and nucleic acid synthesis was reduced to about 50% of the control value at this time. sec-Butylamine inhibited the incorporation of labeled carbon from [¹⁴C]glucose into the protein fraction of the hyphae to a greater degree than ¹⁴C derived from labeled proline, lysine, or leucine. These observations suggested that sec-butylamine interfered primarily with the intermediary metabolism of glucose rather than inhibiting a later stage of macromolecule synthesis. Hyphae incubated with [¹⁴C]glucose and sec-butylamine accumulated pyruvic acid to a level seven times greater than in control hyphae. Furthermore, sec-butylamine strongly inhibited ¹⁴CO₂ evolution from hyphae metabolizing [¹⁴C]pyruvate whereas CO₂ derived from acetate or glucose after a 45-min incubation was only slightly reduced by sec-butylamine. These observations implicate pyruvate oxidation as the primary site of sec-butylamine action in young hyphae of P. digitatum.