Enhancement of Ca2+-sensitive myosin ATPase activity by cadmium.
The effects of Cd2+ on Ca2+-sensitive myosin ATPase activity were examined. In the absence of Ca2+, the Ca2+-dependent myosin ATPase activity was enhanced by Cd2+ to the same extent as with Ca2+ at concentrations ranging from 10(-6) to 10(-3) M. At 10(-2) M, however, no activation was observed. Zn2+, Co2+, and Sr2+ also activated the myosin ATPase. Sr2+ and Co2+ were less effective. Hg2+, Cr3+, and Cu2+ were essentially inactive. In the presence of below 10(-3) M Ca2+, the increase in the enzyme activity observed on the addition of Cd2+ was in addition to that caused by Ca2+ alone. The ability of metal ions to activate myosin ATPase was compared with that to activate calmodulin-dependent cAMP phosphodiesterase. The activating effects of the metal ions tested were in the order of Ca2+ greater than Cd2+ greater than Zn2+ greater than Co2+ greater than Sr2+ for Ca2+-sensitive myosin ATPase and Ca2+ greater than Cd2+ greater than Sr2+ greater than Zn2+ greater than Hg2+ greater than Co2+ for cAMP phosphodiesterase. Cd2+ activated both enzyme activities most efficiently among the metal ions tested except Ca2+. These results indicate that Cd2+ is able to substitute for Ca2+ in the case of Ca2+ dependent enzymes, regardless of whether or not calmodulin participates in the activating process.
Nimura
E
E
Department of Public Health, School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan.
Miura
K
K
Shinobu
L A
LA
Imura
N
N
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002104:Cadmium / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology; D002417:Cattle; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D008670:Metals / Q000494:pharmacology; D011817:Rabbits
D002147:Calmodulin; D008670:Metals; D002104:Cadmium; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1; D000251:Adenosine Triphosphatases; D002118:Calcium