Transport of phenylalanine by conidia of Fusarium sulphureum

Abstract

L-Phenylalanine was actively transported by conidia of Fusarium sulphureum Schlect (isolate 1). Uptake was optimal at pH 7, 30 °C; respiration-dependent; and was unaffected by relatively high internal concentrations of phenylalanine. The Km for transport was 1–3 × 10−5 M and the Vmax was 2.5–4 nmol/min per milligram dry weight. Phenylalanine is transported by a general transport system for basic and neutral amino acids. Sucrose repressed uptake of phenylalanine and this repression was largely negated by cycloheximide. Efflux of accumulated phenylalanine was influx-dependent; this transport system deteriorated slowly with aging of the conidial culture.