Uptake and Utilization of Glutamic Acid by Cryptococcus albidus

Abstract

Cryptococcus albidus utilizes glutamate as a sole carbon source. The kinetics of uptake of this amino acid were studied. l -Glutamic acid was taken up by two saturable systems: a high affinity system with a Michaelis constant ( K m ) of 1.15 × 10 −5 M and a V max of 0.049 μmol per mg per h and a low affinity system with a K m of 2.5 × 10 −3 M and a V max of 3.61 μmol per mg per h. Both systems possessed characteristics of active transport which were dependent on temperature and pH and which required metabolic energy. Uptake was inhibited at 37 C but the temperature-sensitive step was reversible. Chemical fractionation of cells with 5% trichloroacetic acid showed that glutamic acid initially entered a soluble pool which decreased after 1 h as the amino acid was incorporated into the protein and nucleic acid fractions of the yeast. Some of the glutamate was completely oxidized and could be recovered as 14 CO 2 . Therefore, the amino acid was also used as an energy source.