Effect of manganous and magnesium ions concentration on glutamine synthetase and glutamotransferase of sheep brain.

This transfer reaction is activated by Mn++, and its optimal pH was found to be 5.5 (2, 3). The possibility exists that the synthesis and transfer reactions are catalyzed by the same enzyme (4-6). Elliott (1) found that synthesis by the sheep brain enzyme at pH 7.1 occurred with low concentrations of Mn++, and observed that synthesis with Mn++ reached a maximum of 46 per cent of that obtained in the presence of Mg++. Higher concentrations of Mn++ inhibited the synthesis. We found, however, that the concentration of Mn++ necessary for optimal activation of the synthesizing reaction changes with pH, and that Mn++ concentrations which were strongly inhibitory at pH 7.2 readily activated the synthesis at more acidic pH values. A decrease in Mn++ concentration caused a shift of the optimal pH of the transfer reaction from 5.5 toward the alkaline region. We also found that when the transfer reaction is activated by Mg++ instead of Mn++, the optimal pH lies at about 7.2. A preliminary account of some of these observations has been given previously (7). In the present paper the details of these studies are described.