Highsmith S, Bloebaum P, Smith D, Claydon N
Department of Biochemistry, School of Dentistry, University of the Pacific, San Francisco, CA 94115.
Arch Oral Biol. 1987;32(10):745-9. doi: 10.1016/0003-9969(87)90120-8.
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.
大鼠切牙成牙本质细胞的匀浆具有Ca2+和Mg2+ATP酶活性，适宜的储存条件可使其在数天内保持稳定。超过90%的活性保留在富含囊泡的微粒体组分中，该组分从匀浆中去除了约85%的总物质。对该组分进行了进一步表征：在基础MgATP酶活性之上，分辨出的Ca2+激活的ATP酶活性为0.30μmol Pi/分钟-毫克总蛋白，在游离[Ca2+]等于0.8μM时50%被激活。这种钙依赖性与细胞内Ca2+调节的酶活性一致。钙离子载体A23187对CaATP酶活性没有可测量的影响，这表明成牙本质细胞囊泡不会在脂质双层区室中浓缩Ca2+。通过过滤法直接测量45Ca2+的摄取，并在相同条件下对相同制剂平行测量CaATP酶活性，结果表明成牙本质细胞来源的囊泡的偶联比为0.024 Ca2+/ATP。这种低偶联比以及缺乏可检测到的钙区室化表明，成牙本质细胞微粒体的CaATP酶活性与钙泵无关。该活性对[Ca2+]的依赖性表明CaATP酶受细胞内Ca2+控制，但其功能尚不清楚。
