L-phenylalanine ammonia-lyase (E.C. 4.3.1.5., PAL) from the red basidiomycetous yeast. Rhodosporidium toruloides was partially purified using protamine sulfate, ammonium sulfate fractionation, and DEAE-Sephacel column chromatography steps. The resulting preparation was tenfold purified over the crude extract with an estimated purity of at least 60%. This preparation departed from Michaelis-Menten kinetics (K-m(high) = 1,280 mu M and K-m(low) = 150 mu M). The stability of partially purified PAL preparations in water (pH 8.0) to heating was examined and half-lives of 95 h at 30 degrees C, 21 h at 50 degrees C, and 1.4 min at 70 degrees C were obtained. The rate of inactivation at 6-degrees C was found to depend markedly on the pH of the PAL solution, with stability falling sharply either side of the range 5.5-7.0. Inactivation rates of solid lyophilized PAL powders at 30 degrees C increased at higher water activities. Powders exposed to several dry or water-saturated organic solvents revealed that solvent hydrophobicity was not the sole determinant of enzyme stability. The effects of PAL stability of increasing the carbon chain lengths of both n-alkanes and n-alcohols and the water content of n-octanol were also examined.