Proline Uptake in Candida albicans

Abstract

391~ L-Proline entered both mycelial and yeast cells of Candida albicans by an active transport system of high specificity at low ((0.1 mM) external concentrations of substrate. The apparent K, value of this system was 0-1 mM for both types of cells, while the Vvalue was 4 nmol min-' (mg dry wt)-' for mycelial cells and 1-4 nmol min-l (mg dry wt)-' for yeast cells. At L-proline concentrations greater than 0-1 mM, the amino acid appeared to enter both morphological forms by diffusion as well as active transport. As saturation was approached diffusion became increasingly important. The higher uptake rate of mycelial cells seemed not to be the result of an inducible system. The optimal pH and temperature for transport of L-proline were 7-0 and 37 O C , respectively. Sodium azide and the proline analogues sarcosine and L-azetidine-Zcarboxylic acid inhibited L-proline uptake, while ~-thiazolidine-4-carboxylic acid was less effective. The active transport system was highly specific for L-proline since neither ammonium ions, which inhibit the general amino acid transport system of fungi, nor 16 different amino acids interfered substantially with uptake.

Proline-induced Germ-tube Formation in Candida albicans: Role of Proline Uptake and Nitrogen Metabolism

“…Characterization of the proline uptake system showed it to be constitutive, as found by Dabrowa & Howard (1981) and Jayakumar et al (1979), specific, confirming the results of Dabrowa & Howard (1981), and partially inducible in that preincubation in proline increased uptake, a finding also reported by Jayakumar et al (1979). We also found that proline uptake was subject to ammonium repression; removal of nitrogen from the medium resulted in an increase of the proline uptake rate in both the presence and absence of glucose.…”

“…Verma & Prasad (1983) found no evidence for ammonium repression of the uptake of a number of amino acids or the imino acid proline in C. albicans, but it has been demonstrated in S. chevalieri , S. cerevisiae (Lasko & Brandriss, 1981) and Aspergillus nidulans (Arst et al, 1980). The difference in uptake rates between yeast and mycelial cells found by Dabrowa & Howard (1981) may have reflected derepression occurring in the mycelial cultures before the uptake determination.…”

“…The nitrogen source was 10 ~M-(NH,),SO, unless otherwise stated. To prepare cells for optimal germ-tube formation, cultures were starved by aeration in distilled water (Shepherd et al, 1980); germ-tube formation was induced by incubation at 37°C in 1 0 m~-imidazole buffer at a cell concentration of 1.5-2.0 x lo7 cells ml-* with either 2.5 mM-GlcNAc (Shepherd et al, 1980) or I0 mM-proline (Dabrowa & Howard, 1981). Germ-tube formation was assessed by phase-contrast microscopy after dispersal of cell aggregates by mild sonication (10-15 s) in 0.1 M-NaOH containing 1% (w/v) SDS.…”

CAP1 , an Adenylate Cyclase-Associated Protein Gene, Regulates Bud-Hypha Transitions, Filamentous Growth, and Cyclic AMP Levels and Is Required for Virulence of Candida albicans

“…Yeast forms were grown in yeast extract peptone dextrose (YPD) or a yeast nitrogen base containing 50 mM glucose (YNB) (66). Mass conversion of stationary-phase yeasts (grown at 30°C for 48 h) to germ tubes was induced at 37°C in the following prewarmed media: Lee's (pH 6.8) (45), medium 199 (Gibco-BRL) with 150 mM HEPES (pH 7.0) (M199), M199 containing 5% bovine calf serum (Sigma) (M199ϩserum), 50 mM potassium phosphate (pH 6.0) plus 10% bovine calf serum (23), and 10 mM imidazole-HCl buffer (pH 7.0) containing 0.2 mM MnCl 2 (with the following inducing agents: 4 mM N-acetylglucosamine, 10 mM L-proline plus 10 mM glucose, or 2.5 mM glutamine plus 2.5 mM glucose) (18,49,71). Whole human saliva was collected on ice and clarified by centrifugation at 10,000 ϫ g for 15 min at 4°C (37).…”

The Cek1 and Hog1 Mitogen-Activated Protein Kinases Play Complementary Roles in Cell Wall Biogenesis and Chlamydospore Formation in the Fungal Pathogen Candida albicans

“…These types of morphologies have distinct abilities to adhere, proliferate, invade, or escape phagocytic cells and, therefore, contribute by different degrees to the pathogenesis of the infection. The transfer from the yeast form to the filamentous form of growth is induced by certain chemicals (14,18,20,48), a temperature close to 37°C (30), and a neutral pH (49), while chlamydospore formation is induced in vitro under special conditions, such as a low concentration of glucose, darkness, low temperature (24 to 28°C) and microaerophilia.The molecular mechanisms involved in the regulation of polymorphism in C. albicans are very complex. Genetic analysis has shown the implication of several genes and regulatory cascades in this process (31,37,54,56).…”