Abstract
Sciatic nerves from cat contain a relatively high level of Mg
2+
Ca
2+ activated ATPase (MgCa ATPase). The enzyme was found by subcellular fractionation to be present for the most part in the particulate fraction (61.5%) and to a lesser extent in the mitochondrial fraction (21.4%). The high speed supernatant fraction contains the least amount (7.6%).
In decreasing order of effectiveness MgCa ATPase hydrolyzes ATP, GTP, UTP, ITP and CTP with ADP, UDP, IDP and CDP hydrolyzed to a small extent and neither AMP or cyclic AMP effective as substrates.
The enzyme was activated either by Mg
2+ or Ca
2+ at an optimum concentration of3.0m
M. It had a
K
m
of 4.8 × 10
−4 with an optimum pH of 7.4. It was inhibited by mersalyl, PCMP, iodoacetate and dinitrophenol. Oligomycin did not block its action, nor did the mitotic blocking agents colchicine and vinblastine to any great extent.
Approximately 54% of the enzyme present in the particulate fraction could be solubilized by Triton X-100, and a molecular weight of 150,000 was tentatively assigned to it on the basis of Sephadex G-200 gel filtration.
The enzyme is carried down within nerve fibers by slow axoplasmic transport as shown by its accumulation over a period of 5–30 days above ligations made in cat sciatic nerves.