Some general characteristics of the transport of nutrients and toxic compounds in yeasts and fungi

Purified arginine permease of Candida albicans is functionally active in a reconstituted system

We have for the first time purified arginine permease from a pathogenic yeast, Candida albicans, to homogeneity by affinity chromatography using L-arginine-linked agarose matrix as affinity column. The purified protein (PP) was of 66 kDa with no subunit structure. Two kinetically distinct binding affinities of PP were evident where high affinity binding (S1) revealed a dependence on acidic pH while pH did not have dramatic effect on low affinity (S2) binding. The specificity of L-arginine binding to PP with regard to other amino acids, structural analogues and inhibitors, was essentially similar to arginine transport observed in the intact cells of C. albicans (Rao et al., 1986). The purified arginine permease was reconstituted into proteoliposomes and its functionality was tested by imposing a valinomycin-induced membrane potential. All the characteristic features of L-arginine transport displayed by the reconstituted system were similar to those observed in intact cells. Thus homogeneous purified arginine permease was also functionally active.

Transport of small lons and molecules through the plasma membrane of filamentous fungi

Less than 1% of the estimated number of fungal species have been investigated concerning the transport of low-molecular-weight nutrients and metabolites through the plasma membrane. This is surprising if one considers the importance of the processes at the plasma membrane for the cell: this membrane mediates between the cell and its environment. Concentrating on filamentous fungi, in this review emphasis is placed on relating results from biophysical chemistry, membrane transport, fungal physiology, and fungal ecology. Among the treated subjects are the consequences of the small dimension of hyphae, the habitat and membrane transport, the properties of the plasma membrane, the efflux of metabolites, and the regulation of membrane transport. Special attention is given to methodological problems occurring with filamentous fungi. A great part of the presented material relies on work with Neurospora crassa, because for this fungus the most complete picture of plasma membrane transport exists. Following the conviction that we need "concepts instead of experiments", we delineate the lively network of membrane transport systems rather than listing the properties of single transport systems.

Effect of calcium channel blockers on the action of various antitumour agents in the yeast Saccharomyces cerevisiae

The cytotoxic effects of a 22 h treatment with four antineoplastic agents in the yeast Saccharomyces cerevisiae ATCC 2366 were investigated. Two agents, doxorubicin and 5-fluorouracil (5-FU), were effective in decreasing the colony-forming ability of yeast cells. Following examination under the light microscope, the effect of doxorubicin appeared to be, at least partially, due to killing of yeast cells whereas the effect of 5-FU was rather due to changes in cell structure leading to abnormal bud formation. For amsacrine (AMSA) and melphalan, cytotoxicity was totally absent. In the presence of diltiazem the above described effects were not significantly changed. When verapamil was added in the culture medium the cytotoxic activity of doxorubicin and 5-FU did not change. However, following treatment with AMSA in combination with verapamil, cell survival was significantly decreased whereas the presence of verapamil increased the yeast survival which was observed after melphalan treatment.

Resistance to arsenic compounds in microorganisms

Arsenic ions, frequently present as environmental pollutants, are very toxic for most microorganisms. Some microbial strains possess genetic determinants that confer resistance. In bacteria, these determinants are often found on plasmids, which has facilitated their study at the molecular level. Bacterial plasmids conferring arsenic resistance encode specific efflux pumps able to extrude arsenic from the cell cytoplasm thus lowering the intracellular concentration of the toxic ions. In Gram-negative bacteria, the efflux pump consists of a two-component ATPase complex. ArsA is the ATPase subunit and is associated with an integral membrane subunit, ArsB. Arsenate is enzymatically reduced to arsenite (the substrate of ArsB and the activator of ArsA) by the small cytoplasmic ArsC polypeptide. In Gram-positive bacteria, comparable arsB and arsC genes (and proteins) are found, but arsA is missing. In addition to the wide spread plasmid arsenic resistance determinant, a few bacteria confer resistance to arsenite with a separate determinant for enzymatic oxidation of more-toxic arsenite to less-toxic arsenate. In contrast to the detailed information on the mechanisms of arsenic resistance in bacteria, little work has been reported on this subject in algae and fungi.

Involvement of potassium ions in the action of various antineoplastic drugs on the growth of Saccharomyces cerevisiae

The involvement of potassium ions in the action of some antineoplastic drugs on the growth of Saccharomyces cerevisiae was studied by incubating yeast cells in the presence of drugs at various concentrations and KCl at concentrations of 50 mmol l-1 and 100 mmol l-1. The presence of 6.25-50 micrograms ml-1 amsacrine or melphalan alone in the culture medium had no significant effect on yeast growth. Addition of KCl significantly increased the sensitivity to these drugs. On the contrary, incubation of yeast cells with KCl had no effect on the cytotoxic action of doxorubicin, methotrexate or 5-fluorouracil.