title: Quantitative determination of Ca2+-dependent Mg2+-ATPase from sarcoplasmic reticulum in muscle biopsies.
abstract: The possibility of quantifying the total concentration of Ca2+-dependent Mg2+-ATPase of sarcoplasmic reticulum was investigated by measurement of the Ca2+-dependent steady-state phosphorylation from [gamma-32P]ATP and the Ca2+-dependent 3-O-methylfluorescein phosphatase (3-O-MFPase) activity in crude muscle homogenates. The Ca2+-dependent phosphorylation at 0 degree C (mean +/- S.E.) was 40.0 +/- 2.5 (n = 6) and 6.2 +/- 0.7 (n = 4) nmol/g wet wt. in rat extensor digitorum longus (EDL) and soleus muscle, respectively (P less than 0.001). The Ca2+-dependent 3-O-MFPase activity at 37 degrees C was 1424 +/- 238 (n = 6) and 335 +/- 56 (n = 4) nmol/min per g wet wt. in rat EDL and soleus muscle, respectively (P less than 0.01). The molecular activity calculated from these measurements amounted to 35 +/- 5 min-1 (n = 6) and 55 +/- 10 min-1 (n = 4) for EDL and soleus muscle respectively. These values were not different from the molecular activity calculated for purified Ca2+-ATPase (36 min-1). The Ca2+-dependent 32P incorporation in soleus muscle decreased in the order mice greater than rats greater than guinea pigs. In EDL muscles from hypothyroid rats at a 30% reduction of the Ca2+-dependent phosphorylation was observed. The Ca2+-dependent phosphorylation in vastus lateralis muscle from three human subjects amounted to 4.5 +/- 0.8 nmol/g wet wt. It is concluded that measurement of the Ca2+-dependent phosphorylation allows rapid and reproducible quantification of the concentration of Ca2+-dependent Mg2+-ATPase of sarcoplasmic reticulum. Since only 20-60 mg of tissue is required for the measurements, the method can also be used for biopsies obtained in clinical studies.
authors.affiliation: Institute of Physiology, University of Aarhus, Denmark.
authors.forename: M E
authors.initials: ME
authors.lastname: Everts
authors.forename: J P
authors.initials: JP
authors.lastname: Andersen
authors.forename: T
authors.initials: T
authors.lastname: Clausen
authors.forename: O
authors.initials: O
authors.lastname: Hansen
mesh_terms: D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000032:analysis*; D000252:Calcium-Transporting ATPases / Q000032:analysis*; D005260:Female; D006168:Guinea Pigs; D006801:Humans; D007037:Hypothyroidism / Q000201:enzymology; D008722:Methods; D051379:Mice; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D010750:Phosphoproteins; C045349:3-O-methyl-fluorescein phosphatase; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase