Membrane enzyme systems molecular size determinations by radiation inactivation

Target Molecular Size of the Red Beet Plasma Membrane ATPase

“…This mol wt is similar to that observed for the catalytic subunit of the animal cell Na, K-ATPase (14), the Ca-ATPase of the sarcoplasmic reticulum (9), the gastric mucosal H, K-ATPase (10), and the fungal plasma membrane ATPase (12). For (15,16) and low dose rate exposure by y-rays from source irradiators (1,18 (1). In preliminary studies, an irradiator containing 1000 Ci of '37Cs was used; however, subsequent studies were carried out using an irradiator containing 5000 Ci of '37Cs.…”

“…The Na, K-ATPase is believed to be a complex consisting of two 100,000 mol wt catalytic subunits and two 37,000 mol wt noncatalytic glycoproteins (14,16,19,22) while a trimeric (26) or tetrameric (24) arrangement of 100,000 mol wt subunit has been suggested for the gastric mucosal H, K-ATPase. Recent studies have also suggested a dimeric structure for both the Ca-ATPase of the SR3 ( (14), and the Ca-ATPase of the SR (9), evidence has been presented which indicates that the minimal unit of ATP hydrolytic activity is a 100,000 mol wt catalytic subunit (and a 37,000-mol wt glycoprotein in the case of Na, K-ATPase); however, it is unclear whether or not this is also the minimal unit which can couple ATP hydrolysis to ion transport (9,14).…”

Isolation of a digitoxin‐bound protein from a brain membrane preparation containing Na+, K+‐activated ATPase

“…However it is of interest that estimates of molecular weight of the enzyme may be divided into approximately two groups, those estimates in the range 500-560 000 [3,19,20], and those of about 250 000 (8,21). The presence of oligomeric proteins in membrane cannot be inferred from the observation of protein aggregates in the presence of SDS.…”

Radiation inactivation analysis of kidney microvillar peptidases

“…Apparent molecular target sizes were calculated from the empirically established relationship [9] that M, = 6.4 x 105/Ds7, where 037 is the radiation dose expressed in Mrad required to reduce the specific activity of the enzyme to 37% (i.e. l/e) of its original value.…”