The CaATPase activity of rat-incisor odontoblast vesicles.
An homogenate of rat incisor odontoblasts had Ca2+ and Mg2+ ATPase activity and suitable storage conditions kept it stable for several days. Over 90 per cent of the activity was retained in a vesicle-rich microsomal fraction that removed about 85 per cent of the total material from the homogenate. This fraction was further characterized: the resolved Ca2+-activated ATPase activity, above the basal MgATPase activity, was 0.30 mumol Pi/min-mg total protein, and 50 per cent activated at free [Ca2+] equal 0.8 microM. This calcium dependency is consistent with an intracellular Ca2+-regulated enzymatic activity. The calcium ionophore, A23187, had no measurable effect on the CaATPase activity, which suggests that the odontoblast vesicles do not concentrate Ca2+ in a lipid bilayer compartment. Direct measurement of the uptake of 45Ca2+ by the filtration method and parallel measurements of CaATPase activity on the same preparations under identical conditions indicated that the odontoblast-derived vesicles have a coupling ratio of 0.024 Ca2+/ATP. This low coupling ratio and the lack of detectable compartmentalization of calcium indicate that the CaATPase activity of the odontoblast microsomes is not associated with a calcium pump. The [Ca2+] dependence of the activity suggests the CaATPase is under intracellular Ca2+ control, but its function is unknown.
Highsmith
S
S
Department of Biochemistry, School of Dentistry, University of the Pacific, San Francisco, CA 94115.
Bloebaum
P
P
Smith
D
D
Claydon
N
N
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D007180:Incisor; D008297:Male; D008861:Microsomes / Q000201:enzymology*; D009804:Odontoblasts / Q000201:enzymology / Q000648:ultrastructure*; D051381:Rats; D011919:Rats, Inbred Strains; D014617:Vacuoles / Q000201:enzymology
D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases