title: Regulation of sulfate transport in filamentous fungi.
abstract: Inorganic sulfate enters the mycelia of Aspergillus nidulans, Penicillium chrysogenum, and Penicillium notatum by a temperature-, energy-, pH-, ionic strength-, and concentration-dependent transport system ("permease"). Transport is unidirectional. In the presence of excess external sulfate, ATP sulfurylase-negative mutants will accumulate inorganic sulfate intracellularly to a level of about 0.04 m. The intracellular sulfate can be retained against a concentration gradient. Retention is not energy-dependent, nor is there any exchange between intracellular (accumulated) and extracellular sulfate. The sulfate permease is under metabolic control. Sulfur starvation of high methionine-grown mycelia results in about a 1000-fold increase in the specific sulfate transport activity at low external sulfate concentrations. l-Methionine is a metabolic repressor of the sulfate permease, while intracellular sulfate and possibly l-cysteine (or a derivative of l-cysteine) are feedback inhibitors. Sulfate transport follows hyperbolic saturation kinetics with a Michaelis constant (Km) value of 6 x 10(-5) to 10(-4)m and a V(max) (for maximally sulfurstarved mycelia) of about 5 micromoles per gram per minute. Refeeding sulfur-starved mycelia with sulfate or cysteine results in about a 10-fold decrease in the V(max) value with no marked change in the Km. Azide and dinitrophenol also reduce the V(max.).
authors.affiliation: Department of Biochemistry and Biophysics, University of California, Davis, California 95616.
authors.forename: G
authors.initials: G
authors.lastname: Bradfield
authors.forename: P
authors.initials: P
authors.lastname: Somerfield
authors.forename: T
authors.initials: T
authors.lastname: Meyn
authors.forename: M
authors.initials: M
authors.lastname: Holby
authors.forename: D
authors.initials: D
authors.lastname: Babcock
authors.forename: D
authors.initials: D
authors.lastname: Bradley
authors.forename: I H
authors.initials: IH
authors.lastname: Segel