Effect of concanavalin A on the kinetics of ecto-5'-adenosine monophosphatase (5'-adenosine monophosphate phosphohydrolase) in the outer surface of intact neural cells in culture

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Abstract
Oncogenic cultured rat C6 astroblastoma cells display strikingly high ecto-5''-AMPase activity, 4.23 .+-. 20 .mu.mol of Pi liberated by intact cells from 3 mM extracellular 5''-AMP (mg of protein)-1 h-1, as compared with 0.15 .+-. 0.01 for nononcogenic cultured hamster astroblasts. A further rise in C6 cell ecto-5''-AMPase activity occurs with increase in cell density during growth. Of the lectin concanavalin A (Con A) < 2 pg bound per cell reversibly inhibits most of the cellular ecto-5''-AMPase activity. Inhibition by Con A binding is independent of cellular temperature. Con A binding suppresses phosphohydrolase activity of a pK = 7.4 functional group on the cell surface. A direct proportionality is observed between quantity of Con A bound to the cell surface and simultaneous relative decreases both in Km and Vmax of ecto-5''-AMPase in the intact cell. A major consequence of the specific high affinity binding of Con A to the C6 cell surface is probably the inactivation of the enzyme-substrate complex of ecto-5''-AMPase.