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We have investigated the subunit structure of Ca2+-transport ATPase in human erythrocyte membranes using radiation inactivation analysis. All inactivation data were linear on a semilog plot down to at least 20% of the control activity. We found a target size for the calmodulin-dependent Ca2+-ATPase activity of 331 kDa, consistent with the presence of this enzyme as a dimer in calmodulin-depleted ghosts. Membranes which had been saturated with calmodulin before irradiation yield a a similar size of 317 kDa, implying that activation of Ca2+-transport ATPase by calmodulin does not involve significant change in oligomeric structure. Basal (calmodulin-independent) Ca2+-ATPase activity corresponded to a size of 290 kDa, suggesting that this activity resides in the same, or similar-sized, complex as the calmodulin-dependent activity. Mg2+-ATPase activity, however, was found to reside in a smaller complex of 224 kDa, which proved to be statistically distinct from the target size of Ca2+-ATPase activity. It would appear that Mg2+-ATPase is a distinct entity whose function is likely unrelated to the Ca2+-transport ATPase.
L Hymel, and
M Nielsen, and
K Gietzen
December 1980,
Biochimica et biophysica acta,
L Hymel, and
M Nielsen, and
K Gietzen
June 1989,
Bioscience reports,
L Hymel, and
M Nielsen, and
K Gietzen
January 1981,
The Journal of biological chemistry,
L Hymel, and
M Nielsen, and
K Gietzen
January 1982,
Acta radiologica. Oncology,
L Hymel, and
M Nielsen, and
K Gietzen
August 1976,
Biochimica et biophysica acta,
L Hymel, and
M Nielsen, and
K Gietzen
January 1979,
The International journal of biochemistry,
L Hymel, and
M Nielsen, and
K Gietzen
July 1977,
Biochemical and biophysical research communications,
L Hymel, and
M Nielsen, and
K Gietzen
January 1980,
Annals of the New York Academy of Sciences,
L Hymel, and
M Nielsen, and
K Gietzen
March 1981,
Endocrinology,
L Hymel, and
M Nielsen, and
K Gietzen
August 1989,
Molecular and cellular biochemistry,
