Proline and Glycine Betaine Influence Protein Solvation

Abstract

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...

Response of antioxidant enzymes and some metabolic activities in wheat to Fusarium spp. Infections

“…It has been assigned a role as a cytosolute (Stewart and Lee, 1974), as a convenient source of energy (Stewart, 1973) and as a protective agent for cytoplasmic enzymes (Schubert, 1977). In addition, proline can serve as a protector of enzyme denaturation (Paleg et al, 1984), as a reservoir of nitrogen and carbon (Fukutaku and Yamada, 1984) or as a stabilizer of the machinery for protein synthesis (Kardpal and Rao, 1985). A decrease in proline content was detected in wheat plants treated with F. merismoides, F. moniliforme, F. oxysporum, F. poae and F. subglutinans, in agreement with the results obtained by Abdel-Latef (2003) and Azooz et al (2004).…”

Osmotic repression of anaerobic metabolic systems in Escherichia coli

“…Some effects of inorganic ions result from their binding to active sites or from an alteration of protein stability and compartmentalization in the cell structures. Osmolyte protection of enzymes has received much attention (53); various organic compounds, such as betaines, used as osmolytes by organisms, can enhance the stability of proteins and membranes in environments of low water activity (1,10,22,31,34,39). Since the response of anaerobic gene expression to the increase of osmolarity shows a delay compared with that of enzymatic activities ( Fig.…”

Overexpression of [delta]-Pyrroline-5-Carboxylate Synthetase Increases Proline Production and Confers Osmotolerance in Transgenic Plants

“…Pro has been demonstrated to ameliorate dehydrationinduced perturbation in proteins (Paleg et al, 1984), and exogenously supplied Pro confers some osmotic tolerance to the plants and cultured cells (Itai and Paleg, 1982). However, a cause-and-effect relationship between Pro levels and osmotic potential has not been established.…”

“…Both Pro and Gly betaine under water-stressed conditions may be able to induce the formation of strong H-bonded water around the protein, preserving the native state of the cell biopolymers (Rascio et al, 1994). These osmolytes have been suggested to directly influence protein solvation by protecting from dehydration-induced thermodynamic perturbations in proteins (Paleg et al, 1984). Externally added Pro has been demonstrated to protect the structural and functional integrity of enzymes in vitro (Deutch et al, 1984).…”