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1. Adenosine metabolism in human erythrocytes

Author

Meyskens, Frank L and Williams, Hibbard E

Subjects
Biochemistry and Cell Biology, Biological Sciences, Adenine, Adenine Nucleotides, Adenosine Triphosphate, Aminohydrolases, Carbon Isotopes, Chlorides, Deamination, Electrophoresis, Erythrocytes, Guanine Nucleotides, Humans, Hydrogen-Ion Concentration, Hypoxanthines, Kinetics, Magnesium, Nucleosides, Nucleotides, Paper, Phosphates, Phosphoglycerate Kinase, Phosphotransferases, Physical Sciences, Biological sciences, Physical sciences
Abstract

1. 1. The metabolism of [8-14C]adenosine was examined in human erythrocytes and erythrocyte lysates. 2. 2. The metabolism of [8-14C]adenosine in erythrocytes is largely dependent upon its concentration. 3. 3. Adenosine deaminase and adenosine kinase activities were assayed in crude erythrocyte lysates. No adenosine phosphorylase activity was detected. 4. 4. Adenosine deaminase exhibited a Km for adenosine of 4 · 10-5 M. Substrate inhibition of the enzyme was exhibited at concentrations of adenosine greater than 2 · 10-4 M. No inhibition of deaminase activity by equimolar or greater concentration of AMP, ADP, ATP, GDP, GTP, Pi, guanylic acid or 2,3-diphosphoglycerate was noted, but 20 % inhibition by high concentrations of adenine and inosine was observed. 5. 5. Adenosine kinase required ATP (Km = 4 · 10-4 M), adenosine (Km = 1.9 · 10-6 M), and Mg2+ for activity. No substrate inhibition by adenosine occurred at concentrations 20 times its Km. Adenosine 5′-triphosphate and Mg2+ were inhibitory at concentrations greater than 1.25 mM and 0.50 mM, respectively. The reaction of ATP with adenosine kinase was competitively inhibited by AMP, ADP, guanylic acid, GDP, IMP, and adenine. Adenosine 5′-triphosphate was variably replaceable as the phosphate donor by a wide range of triphosphates. © 1971.

Published
1971

2. Adenosine metabolism in human erythrocytes

Author

Hibbard E. Williams and Frank L. Meyskens

Subjects
Electrophoresis, Paper, Erythrocytes, GTP', Adenosine kinase, Biochemistry, Genetics and Molecular Biology (miscellaneous), Phosphates, Adenosine deaminase, Adenosine Triphosphate, Chlorides, Aminohydrolases, medicine, Humans, Magnesium, Inosine, chemistry.chemical_classification, Carbon Isotopes, biology, Adenine Nucleotides, Nucleotides, Adenine, Phosphotransferases, AMP deaminase, Nucleosides, Metabolism, Hydrogen-Ion Concentration, Adenosine, Molecular biology, Guanine Nucleotides, Kinetics, Phosphoglycerate Kinase, Enzyme, chemistry, Biochemistry, Deamination, Hypoxanthines, biology.protein, medicine.drug
Abstract

1. 1. The metabolism of [8-14C]adenosine was examined in human erythrocytes and erythrocyte lysates. 2. 2. The metabolism of [8-14C]adenosine in erythrocytes is largely dependent upon its concentration. 3. 3. Adenosine deaminase and adenosine kinase activities were assayed in crude erythrocyte lysates. No adenosine phosphorylase activity was detected. 4. 4. Adenosine deaminase exhibited a Km for adenosine of 4 · 10−5 M. Substrate inhibition of the enzyme was exhibited at concentrations of adenosine greater than 2 · 10−4 M. No inhibition of deaminase activity by equimolar or greater concentration of AMP, ADP, ATP, GDP, GTP, Pi, guanylic acid or 2,3-diphosphoglycerate was noted, but 20 % inhibition by high concentrations of adenine and inosine was observed. 5. 5. Adenosine kinase required ATP (Km = 4 · 10−4 M), adenosine (Km = 1.9 · 10−6 M), and Mg2+ for activity. No substrate inhibition by adenosine occurred at concentrations 20 times its Km. Adenosine 5′-triphosphate and Mg2+ were inhibitory at concentrations greater than 1.25 mM and 0.50 mM, respectively. The reaction of ATP with adenosine kinase was competitively inhibited by AMP, ADP, guanylic acid, GDP, IMP, and adenine. Adenosine 5′-triphosphate was variably replaceable as the phosphate donor by a wide range of triphosphates.

Published
1971
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