Die Aufnahme der Zucker Sorbose, Fructose und Glucose durch Sorbose-resistente Mutanten von Neurospora crassa

Abstract

Sorbose-resistant mutants of Neurospora crassa, arising spontaneously or after nitrous acid treatment, can be mapped in at least 6 separate geneloci, scattered over the chromosome complement. Neither combined enzymatic optic tests, nor radio-paperchromatography give evidence for altered enzymes of sugar metabolism or gain of the ability to phosphorylate and utilize sorbose in these mutants. The increase of radioactivity of germinated conidia as a function of time of incubation with 14C-labelled sorbose revealed that the mutants have a decreased rate of active (energy-dependent) sorbose uptake as compared to the wildtype. No difference in rate of either fructose or glucose uptake between mutants and wildtype could be found. Uptake of sorbose exhibited saturation kinetics for mutants and wildtype. Km values of the mutants were nearly equal to that of the wildtype; there are indications that Vmax is lowered in some of them. If supernatants of conidia of 2 mutants (sorr Α-1 and sorrB-57), mapping in separate linkage groups and thus representing two separate genes, were added to pregerminated wildtype conidia, their rate of sorbose-uptake was not depressed. These 2 mutants are therefore not of the excretor-type, i. e. they must be transport-defective mutants. Data available so far exclude that the mutants have a defect in a common carbohydrate carrier, or in a carrier specific for sorbose transport. It is concluded that mutants sorr Α-1 and sorr B-57 are permease-mutants, with genes A and B coding for 2 separate permeases or permease-subunits.