Uptake of Cystine by the Yeast Phase of Histoplasma capsulatum

Abstract

This report deals with factors affecting the uptake of cystine by the yeast phase of Histoplasma capsulatum . The kinetics of uptake showed a saturation at 70 μM and an average K m value of 3 × 10 −5 m . The optimal p H and temperature for transport of cystine were 6.5 and 37 C, respectively. The energy of activation was 14.1 kcal/mole, and the temperature coefficient value was 2.1. A requirement for energy supplied by metabolic activity was demonstrated by the inhibition of incorporation of the amino acid by cells preincubated with either 2,4-dinitrophenol or sodium azide. Although uptake was not inhibited by any single amino acid, a combination of amino acids did cause a decrease in uptake. Thus, the data show that the uptake of cystine by yeast cells of H. capsulatum has the characteristics of a system of transport that requires the expenditure of energy by the cells.

Fate of Histoplasma capsulatum in Guinea Pig Polymorphonuclear Leukocytes

“…Blastospores in saline (0.15 M NaCl solution) suspensions rapidly die (22) and efforts have been made to improve the keeping qualities of this widely used diluent by adding other substances to it (16). However, it is likely that the sodium ion is toxic (3), and thus solutions in which this ion does not occur are preferably used in studies where the quantitative viability of the yeast cells is crucial (4,22). The starvation medium (STM) of Williamson and Scopes (21) has proven of great value as a diluent for blastospores of H. capsulatum (4,22).…”

“…Growth from the slants was harvested in 0.15 M NaCl solution and standardized as described in earlier reports (6,7). In work with horseradish peroxidase and in some of the work with guinea pig granule lysates the salt solution of low ionic strength (STM) previously reported (4) was used to prepare the suspensions. The STM contained 0.01 M KCl; 0.0024 M CaCl2; 0.0025 M MgCl,, and was sometimes used as a buffer by adding 0.05 M tris (hydroxymethyl)-aminomethane (Tris) base and hydrochloric acid.…”

Uptake and Utilization of Glutamic Acid by Cryptococcus albidus

“…C. albidus was grown in Littman's capsular broth (21) incubated at room temperature on a rotary action shaker (model V, New Brunswick Scientific Co., New Brunswick, N.J.) for 24 h. Cells were harvested by centrifugation at 2,600 x g for 15 min at 4 C, washed once, and suspended in distilled water. A calibration curve relating turbidity and dry weight was prepared according to standard methods (8,15). Throughout these studies the cell suspension contained 0.4 mg (dry weight) of Littman thiamine-basal salts medium (thiamine-BSM) per ml (21).…”

Incorporation of Cystine by Yeast Cells of Histoplasma capsulatum

“…However, certain nutritional factors are also known to play a role (13). Among such factors, the sulfur-containing amino acids cysteine and cystine are of cardinal importance in maintenance of yeast phase growth (3,6,12,13). Our previous studies have shown that the uptake of cystine by blastospores of H. capsulatum has the characteristics of a system of transport that requires the expenditure of energy by the cells (3).…”

“…Among such factors, the sulfur-containing amino acids cysteine and cystine are of cardinal importance in maintenance of yeast phase growth (3,6,12,13). Our previous studies have shown that the uptake of cystine by blastospores of H. capsulatum has the characteristics of a system of transport that requires the expenditure of energy by the cells (3). The present studies were undertaken to investigate the incorporation of cystine into certain chemical fractions of H. capsulatum and thus to gain some insight about the role of this amino acid in the expression of dimorphic behavior by the fungus.…”