PURIFICATION AND SOME PROPERTIES OF A THERMOSTABLE ACID ESTERASE FROMACIDIPHILIUM SP. AIU-409

Extracellular and cell-bound esterases produced by Acidiphilium sp. AI U 409 were homogeneously purified from culture broth and cells, respec tively, and some properties were investigated. Both esterases more rap idly hydrolyzed p-nitrophenyl acyl esters containing long-chain fatty acids from C 8:0 to C 18:0 than those containing short-chain fatty aci ds from C 2:0 to C 6:0. The Km values for p nitrophenyl long-chain fat ty acid esters from C 8:0 to C 18:0 were approximately 1.3-1.5 mM. The enzymes were stable at 50 degrees C for 2 days between pH 3.0 and 6.5 , and optimum pH and temperature were 5.0 and 70 degrees C, respective ly. Enzyme activity was inhibited by phenylmethylsulfonyl fluoride and SDS. The molecular mass of both enzymes was estimated to be approxima tely 64 kDa by SDS-PAGE. The 23 amino acid sequence from the NH2-termi nus was also the same in both enzymes. These results suggest that extr acellular esterase might be composed of the same components as cell-bo und esterase.