Characterization of the extracellular ribonuclease of Tetrahymena pyriformis W.
Several investigations have indicated that Tetrahymena pyriformis secretes ribonuclease activity into culture media. The extracellular ribonuclease from strain W has been purified and partially characterized. The molecular weight was determined by gel filtration to be 26,500. The amino acid composition of the enzyme was compared with those of the three intracellular ribonucleases characterized by Trangas, and substantial differences were demonstrated. The extracellular enzyme hydrolyzed both polyadenylic and polyuridylic acids, indicating lack of absolute base specificity. The hydrolysis of polyadenylic acid followed normal Michaelis-Menten kinetics, but substrate inhibition occurred at high concentrations of polyuridylic acid. The hydrolysis of polyuridylic acid was competitively inhibited by 2'- and 3'-cytidine, guanine, and uridine nucleotides, and by 2'AMP. No inhibition of the hydrolysis of Torula yeast RNA was detected. The kinetic properties of the extracellular ribonuclease are compared with those of the intracellular enzymes.
Department of Biology, Bryn Mawr College, Pennsylvania 19010.
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McKee
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Prescott
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002855:Chromatography, Thin Layer; D004591:Electrophoresis, Polyacrylamide Gel; D007525:Isoelectric Focusing; D007700:Kinetics; D008970:Molecular Weight; D012260:Ribonucleases / Q000737:chemistry / Q000378:metabolism*; D013769:Tetrahymena pyriformis / Q000201:enzymology*
D000596:Amino Acids; D012260:Ribonucleases