Glutamine synthetase from barley (Hordeum disticeaim L.) is precipitated by polyethylene glycol (PEG). Proline, in a concentration-dependent manner, reduces the amount of enzyme precipitated by PEG, although the effect of the imino acid can be counteracted by raising the level of PEG. The effect of PEG is a function of mer number and concentration and the influence of both elements can be ameliorated by proline. PEGinduced enzyme precipitation is a function of pH, as is its interaction with both proline and betaine in the reaction. The lack of effect of amount of enzyme on the proline and PEG effects supports the conclusion that, in this system, proline and PEG do not function through interaction with the protein. Other compounds, such as glycine, glucose, and sucrose, can decrease the PEG-induced precipitation of the enzyme, although glycerol was not active under the conditions employed.The results are consistent with the proposition that a protein-containing system in which high concentrations of proline and/or betaine are present, is better 'protected' against the biologically unfavorable consequences of dehydration-induced thermodynamic perturbation.The accumulation of the imino acid, proline, in the free uncombined form is a characteristic response of many plants to many types of stress (3). The interpretation of this response has varied from its description as a useful criterion for the selection of varieties suited to arid areas (27) to nothing more than a measure of the rate of senescence (9). Choosing between these extreme interpretations is difficult since plants cannot be deprived of proline, and external applications are confounded by hydration and penetration problems on the one hand, and metabolism and compartmentation of the applied compound on the other.Recent attempts to demonstrate a conceptually useful role for the accumulated proline (which may reach submaximum levels as high as 0.1-0.3 M in the wheat apex [17] or 5-10% of the dry weight of halophytic tissue [281) have centered on the amelioration of deleterious effects of heat, pH, salt, and chemicals on enzyme activity in in vitro and organelle systems (1,4,19,21,22,35). In all cases reported, significant and, indeed, important proline concentration-dependent protection against a range of perturbing or stressful conditions was afforded to several enzymes. among, if not the most prominent, and is clearly one which causes large scale proline accumulation. No in vitro system has been described with which deleterious effects of dehydration on enzyme activity can be measured, and, thus, it has not been possible to directly test the hypothesis that proline may diminish the effect of dehydration on enzymes and/or enzyme activity. Nonetheless, solvation effects do influence thermodynamic activation parameters ofenzymes (8, 13) and any component which has the ability to effect enzyme solvation may also be expected to influence enzyme activity.A system with which to test the ability of proline to effect enzyme solvation was developed from the...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.