Size of the plasma membrane H+-ATPase from Neurospora crassa determined by radiation inactivation and comparison with the sarcoplasmic reticulum Ca2+-ATPase from skeletal muscle.
Using radiation inactivation, we have measured the size of the H+-ATPase in Neurospora crassa plasma membranes. Membranes were exposed to either high energy electrons from a Van de Graaff generator or to gamma irradiation from 60Co. Both forms of radiation caused an exponential loss of ATPase activity in parallel with the physical destruction of the Mr = 104,000 polypeptide of which this enzyme is composed. By applying target theory, the size of the H+-ATPase in situ was found to be approximately 2.3 X 10(5) daltons. We also used radiation inactivation to measure the size of the Ca2+-ATPase of sarcoplasmic reticulum and got a value of approximately 2.4 X 10(5) daltons, in agreement with previous reports. By irradiating a mixture of Neurospora plasma membranes and rabbit sarcoplasmic reticulum, we directly compared the sizes of these two ATPases and found them to be essentially the same. We conclude that both H+-ATPase and Ca2+-ATPase are oligomeric enzymes, most likely composed of two approximately 100,000-dalton polypeptides.
Bowman
B J
BJ
Berenski
C J
CJ
Jung
C Y
CY
D000818:Animals; D000252:Calcium-Transporting ATPases / Q000032:analysis* / Q000528:radiation effects; D002462:Cell Membrane / Q000201:enzymology; D004583:Electrons; D005720:Gamma Rays; D046911:Macromolecular Substances; D008970:Molecular Weight; D009132:Muscles / Q000201:enzymology*; D009491:Neurospora / Q000201:enzymology*; D009492:Neurospora crassa / Q000201:enzymology*; D006180:Proton-Translocating ATPases / Q000032:analysis* / Q000528:radiation effects; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
D046911:Macromolecular Substances; D006180:Proton-Translocating ATPases; D000252:Calcium-Transporting ATPases