Kinetic properties of the [Ca2+ + Mg2+]-ATPase in Alzheimer and normal fibroblasts at low free calcium.

Kinetic properties of the [Ca2+ + Mg2+]-ATPase from one Alzheimer (AG0364B, 53-year-old donor) and one control fibroblast cell line (AG6009, 59-year-old donor) were examined. A saturation plot revealed the control fibroblast ATPase activity to saturate at approximately 500 nM free Ca2+; whereas, the Alzheimer activity saturated at approximately 1000 nM. Eadie Hofstee graphical analysis indicated almost identical Vmax values, 19.5 and 21.0 nmoles phosphate released/min/mg protein for the Alzheimer and control fibroblasts, respectively. However, an approximately two-fold higher Km value of 350 nM was observed for the Alzheimer fibroblast homogenate in contrast to 220 nM for the control. In a previous study, a kinetic difference in Alzheimer fibroblast [Ca2+ + Mg2+]-ATPase activity at high free Ca2+ concentration was observed. The difference in affinity reported in this study at low free Ca2+ concentrations supports further the hypothesis that abnormalities in Ca2+ homeostasis might be involved in the etiology of Alzheimer's disease.