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STUDIES OF THE MECHANISM OF CATION TRANSPORT
Author(s) -
Charnock JS,
Post RL
Publication year - 1963
Publication title -
australian journal of experimental biology and medical science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.999
H-Index - 104
eISSN - 1440-1711
pISSN - 0004-945X
DOI - 10.1038/icb.1963.45
Subject(s) - chemistry , ouabain , potassium , sodium , magnesium , enzyme , triphosphatase , choline , stimulation , microsome , strophanthin , enzyme assay , reagent , calcium , biochemistry , organic chemistry , medicine
SUMMARY The distribution and activity of adenosine‐triphosphatase in homogenates and subtractions of guinea pig kidney cortex has been examined. A portion of the activity associated with particulate fractions could be further stimulated, in the presence of magnesium ions, by the combined addition of sodium and potassium ions but not by the addition of either cation alone or in combination with choline. Treatment of the heavy microsome subfraction with deoxycholate resulted in a large increase in the specific activity of this enzyme, which now required sodium and potassium ions in a ratio of 4 : 1 for over 85 p.c. of its total activity. Under such conditions of cation stimulation, optimum pH was found to be between 7.5 and 8.0, and the enzyme also exhibited considerable temperature dependence and was stable up to 55°C. The cardiac glycoside Ouabain completely inhibited that portion of enzyme activity stimulated by monovalent cations but was without effect on the activity observed in the presence of magnesium ions alone. The effect of other reagents and hormones on the cation stimulated adenosine‐triphosphatase activity was also examined, with a discussion of the possible significance of this enzyme in active cation transport.