Determination of phosphodiesterase I activity in human blood serum.
Phosphodiesterase I (EC 3.1.4.1) activity was detected in normal human blood serum. The enzyme is stable at laboratory temperature for three days, but is inactivated at pH less than 7. The pH for optimum activity increases with the substrate concentration (under the conditions used, from pH 9.0 to 10.2) and, conversely, the Km increases with pH and buffer concentration. The enzyme is inhibited by ethylenediaminetetraacetate but not by phosphate (0.1 mol/liter). We developed a simple quantitative method for its determination, based on hydrolysis of the p-nitrophenyl ester of thymidine 5'-monophosphate and subsequent measurement of the liberated p-nitrophenol at 400 nm in NaOH (0.1 mol/liter). Normal values (mean +/- 2 SD) were determined to be 33 +/- 6.4 U/liter. Preliminary studies indicate that phosphodiesterase I activity is greater than normal in serum of patients with necrotic changes in the liver or kidney or in cases of breast cancer, but not in that of patients with myocardial infarction, bone cancer, lung cancer, or chronic liver cirrhosis.
D000469:Alkaline Phosphatase / Q000097:blood; D001859:Bone Neoplasms / Q000201:enzymology; D001943:Breast Neoplasms / Q000201:enzymology; D004492:Edetic Acid / Q000494:pharmacology; D005260:Female; D006801:Humans; D007700:Kinetics; D008103:Liver Cirrhosis / Q000201:enzymology; D008175:Lung Neoplasms / Q000201:enzymology; D008297:Male; D009203:Myocardial Infarction / Q000201:enzymology; D009596:Nitrophenols; D010710:Phosphates / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors; D010727:Phosphoric Diester Hydrolases / Q000097:blood*; D013942:Thymine Nucleotides
D009596:Nitrophenols; D010710:Phosphates; D010726:Phosphodiesterase Inhibitors; D013942:Thymine Nucleotides; D004492:Edetic Acid; D000469:Alkaline Phosphatase; D010727:Phosphoric Diester Hydrolases