| Abstract: | Abstract– The isolation of a plasma membrane fraction from the bovine adrenal medulla and its characterization are described. The plasma membranes are enriched 13-fold in AChE, a plasma membrane marker, and represent 0.7% of the homogenate membrane protein. The yield of these membranes is typically 10-12% by the criterion of the percentage of total membrane bound AChE in the homogenate. The membranes were characterized as to their polypeptide, phospholipid and cholesterol content and compared with chromaffin vesicle, mitochondrial and microsomal membranes by these parameters. Two enzymatic components of the plasma membranes, ATPase and adenylate cyclase, were also studied. Calcium ATPase activity is 2.5-fold higher than magnesium ATPase activity, appears to be the result of a single enzyme, and is a genuine component of the plasma membranes. The magnesium stimulated activity appears to have at least two enzymatic components, one of which may be identical to the calcium ATPase. Adenylate cyclase is a plasma membrane component, but may not be uniquely localized there, as it is rather unstable throughout the fractionation procedure. It is stimulated by GTP (0.7-fold at 10?5M), GPP(NH)P (4.8-fold at 10?5M) and sodium fluoride (4.6-fold at 10?2M). It is refractory to stimulation by all other compounds tested. |
