Purification to homogeneity of pyrroline-5-carboxylate reductase of barley.

An enzyme has been purified to homogeneity from barley seedlings which has ;proline dehydrogenase' and the pyrroline-5-carboxylic acid reductase activities. The purification achieved is 39,000-fold as calculated from the proline dehydrogenase activity. The subunit molecular weight of the protein is 30 kilodaltons.

The thermodynamic activity of proline in ternary solutions of different water potentials.

The particular colligative properties of proline caused us to investigate the thermodynamic activity of this amino acid in detail. The dependence of the activity coefficients γ of proline (γ = thermodynamic activity/molality) on the pH of the solutions, the composition of the solution and the water potential has been measured. The results show that the activity coefficient of proline varies according to the solute milieu.

Influence of Water Stress on the Vacuole/Extravacuole Distribution of Proline in Protoplasts of Nicotiana rustica.

Tobacco (Nicotiana rustica) plants were stressed by addition of polyethylene glycol solution (-20 bar) to the growth medium. The proline contents and concentrations in total protoplasts, vacuoles, and extravacuolar fractions of these plants have been determined and compared with protoplasts and cell fractions of well-watered plants. As compared to the control, the stress treatment of intact plants results in a 7-fold increase of the proline content in the extravacuolar fraction while the vacuolar content was enriched only 2.

Glutamate dehydrogenase from peas: isolation, quaternary structure, and influence of cations on activity.

The most active multiple molecular form of glutamate dehydrogenase from pea seeds has been enriched 30000-fold with a recovery of 60--70%. The preparation is homogenous as judged from gel electrophoresis of native and dodecylsulfate-denatured enzyme and from analytical ultracentrifugation. Specific activities were 530 U/mg in the reductive amination and 90 U/mg in the oxidative deamination reaction.

The effect of neutral salt anions on the oxidative deamination activity of plant glutamate dehydrogenase.

Increasing concentrations of anions of the Hofmeister series decrease the activity of highly purified glutamate dehydrogenase (EC 1.4.1.

[On the mechanism of action of glutamate dehydrogenase from pea seedlings and the regulation of the activity by adenosine phosphates, the energy charge and ions].

The mechanism of action and the regulatory properties of glutamate dehydrogenase from pea seedlings (Pisum sativum, var. Späths Violetta) have been investigated by using a highly purified preparation of the enzyme. Kinetic experiments show that the binding of the coenzyme (NAD(+) or NADH) and the substrate (L-glutamate or α-ketoglutarate) is sequential.

[On the mechanism of inhibition of mitochondrial glutamate-oxalacetate-transaminase in SO2-fumigated peas].

The effect of SO2-fumigation on the mitochondrial and cytoplasmic form of GOT in peas has been tested. GOT is represented by two distinct proteins in peas and therefore its activity may be taken as a measure of action of certain effectors on different components of the cell. An optical method for the direct measurement of GOT activity in crude plant extracts has been established.

[Influence of SO on the amino acid metabolism of pea seedlings].

Long-termed fumigation of pea seedlings with SO caused typical alterations of the concentration of free glutamate and glutamine as well as fluctuations of the activity of glutamate dehydrogenase and glutamine synthetase. Shortly after the beginning of the fumigation with low concentrations of SO (up to 0,3 ppm) the amount of glutamate increased. The concentration of glutamine however increases always independently of the concentration of SO.

[Evidence that the multiple molecular forms of glutamate dehydrogenase from pea seedlings are conformers].

The multiple molecular forms of glutamate dehydrogenase from pea seedlings (Pisum sativum, var. Späth's Violetta) have been investigated. When protein preparations are subjected to electrophoresis on polyacrylamide gels, the glutamate dehydrogenase can be localized by substrate staining.

[Allosteric regulation of the activity of glutamate dehydrogenase from pea seedlings by the substrate α-ketoglutarate].

Several investigations on the properties of glutamate dehydrogenase from plant sources indicate that the enzymatic activity (reductive amination) follows a Michaelis-Menten-type kinetic when velocity is plotted versus rising concentrations of the substrate α-ketoglutarate. In the course of our investigations on the effect of SO2 on pea plant enzymes we found that SO 4 (2-) , added as (NH4)2SO4 to the assay system, causes this type of activity response because of its ability to function as an activator. When (NH4)2SO4 is replaced by NH4Cl in the in vitro system however, activity response is sigmoidal.