%0 Journal Article %A Singh, Mahavir %A Sinha, Umakant %T Mode of Action of p-Fluorophenylalanine in Aspergillus nidulans: Effect on the Synthesis and Activity of Phosphatase Isoenzymes %D 1979 %J Microbiology, %V 115 %N 1 %P 101-110 %@ 1465-2080 %R https://doi.org/10.1099/00221287-115-1-101 %I Microbiology Society, %X The polyacrylamide disc gel electrophoretic pattern of five isoenzymes of phosphomono-esterases (both alkaline and acid) of Aspergillus nidulans has been established. Bands I and V are derepressible acid phosphatases, band II is constitutive acid phosphatase, band III a derepressible alkaline phosphatase and band IV a constitutive alkaline phosphatase. Isoenzyme III can be completely inhibited by p-fluorophenylalanine (FPA). Experiments using FPA, cycloheximide and actinomycin D indicated that transcription for isoenzyme III (inhibited by actinomycin D) took place between 20 and 21 h incubation, and translation of the mRNA so formed occurred between 21 and 22 h. FPA and cycloheximide were both inhibitory at the time of translation. However, cycloheximide caused a gradual reduction in the quantity of all isoenzymes, whereas only isoenzyme III was affected by FPA. The different effect of FPA was confirmed by incorporation of radioactive FPA into isoenzyme III. FPA apparently did not inhibit synthesis of isoenzyme III, but inactivated the isoenzyme III formed in its presence. Constitutive isoenzymes synthesized in the presence of FPA showed normal activity. It is suggested that FPA may not necessarily affect the activity of all proteins synthesized in its presence but whenever it is incorporated into indispensable sites in proteins, it inactivates them. This may be the mechanism of growth inhibition by FPA in Aspergillus nidulans. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-115-1-101