TY - JOUR
T1 - The MgATPase activity of rat cardiac sarcoplasmic reticulum is a function of the calcium ATPase protein
AU - Taffet, George
AU - Tate, Charlotte A.
N1 - Funding Information:
’ Supported by NIH (AG06221, AG00428, and HL3870), the Texas Affiliate of the American Heart Association, and The Methodist Hospital Foundation. ’ To whom correspondence should be addressed at Section of Cardiovascular Sciences, Baylor College of Medicine, Houston, Texas 77030. 3498, Fax: (713)796-0015.
PY - 1992/12
Y1 - 1992/12
N2 - Magnesium-dependent ATPase (MgATPase) activity is associated with many E1-E2 or P-type transport ATPases including the sarcoplasmic reticulum (SR) calcium ATPase. The SR isolated from rat heart has a MgATPase activity which is 6-12 times faster than the MgATPase activity of the SR isolated from dog heart. To determine the origin of the high MgATPase activity of rat heart SR, we compared and contrasted cardiac SR isolated from both species. The preparations were similar in the following ways: (i) contamination by other organelles; (ii) the comigration of MgATPase activity with calcium-dependent ATPase (CaATPase) activity through a sucrose gradient; (iii) a similar ATPase activity sensitivity to pH and ATP concentration; (iv) the high and similar of sensitivity of ATPase activity to detergent; and (v) a similar protein profile. In both preparations, a single protein in the 105,000-Da region of polyacrylamide gels was phosphorylated by ATP, and the phosphorylated species was an acylphosphate formed in the presence and absence of calcium. Dimethyl sulfoxide, which slows acylphosphoenzyme breakdown, markedly inhibited both CaATPase and MgATPase activities of both preparations but not other enzyme activities. Importantly, the specific inhibitor of the SR calcium pump, thapsigargin, completely inhibited the CaATPase activity with an I50 of 6-7 nm; however, a higher concentration (I50 of 2 μm) was required to inhibit the MgATPase activity of the rat cardiac SR. These results provide evidence that the Mg-ATPase activity of rat cardiac SR is part of the enzyme cycle of the calcium ATPase protein.
AB - Magnesium-dependent ATPase (MgATPase) activity is associated with many E1-E2 or P-type transport ATPases including the sarcoplasmic reticulum (SR) calcium ATPase. The SR isolated from rat heart has a MgATPase activity which is 6-12 times faster than the MgATPase activity of the SR isolated from dog heart. To determine the origin of the high MgATPase activity of rat heart SR, we compared and contrasted cardiac SR isolated from both species. The preparations were similar in the following ways: (i) contamination by other organelles; (ii) the comigration of MgATPase activity with calcium-dependent ATPase (CaATPase) activity through a sucrose gradient; (iii) a similar ATPase activity sensitivity to pH and ATP concentration; (iv) the high and similar of sensitivity of ATPase activity to detergent; and (v) a similar protein profile. In both preparations, a single protein in the 105,000-Da region of polyacrylamide gels was phosphorylated by ATP, and the phosphorylated species was an acylphosphate formed in the presence and absence of calcium. Dimethyl sulfoxide, which slows acylphosphoenzyme breakdown, markedly inhibited both CaATPase and MgATPase activities of both preparations but not other enzyme activities. Importantly, the specific inhibitor of the SR calcium pump, thapsigargin, completely inhibited the CaATPase activity with an I50 of 6-7 nm; however, a higher concentration (I50 of 2 μm) was required to inhibit the MgATPase activity of the rat cardiac SR. These results provide evidence that the Mg-ATPase activity of rat cardiac SR is part of the enzyme cycle of the calcium ATPase protein.
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U2 - 10.1016/0003-9861(92)90277-4
DO - 10.1016/0003-9861(92)90277-4
M3 - Article
C2 - 1444468
AN - SCOPUS:0027080374
SN - 0003-9861
VL - 299
SP - 287
EP - 294
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
IS - 2
ER -