[The light-induced synthesis of the NADP(+)-dependent glycerin-aldehyde-3-phosphate-dehydrogenase : III. The importance of chlorophyll and the influence of metabolic inhibitors]

Redox regulation of the Calvin-Benson cycle: something old, something new

Reversible redox post-translational modifications such as oxido-reduction of disulfide bonds, S-nitrosylation, and S-glutathionylation, play a prominent role in the regulation of cell metabolism and signaling in all organisms. These modifications are mainly controlled by members of the thioredoxin and glutaredoxin families. Early studies in photosynthetic organisms have identified the Calvin-Benson cycle, the photosynthetic pathway responsible for carbon assimilation, as a redox regulated process. Indeed, 4 out of 11 enzymes of the cycle were shown to have a low activity in the dark and to be activated in the light through thioredoxin-dependent reduction of regulatory disulfide bonds. The underlying molecular mechanisms were extensively studied at the biochemical and structural level. Unexpectedly, recent biochemical and proteomic studies have suggested that all enzymes of the cycle and several associated regulatory proteins may undergo redox regulation through multiple redox post-translational modifications including glutathionylation and nitrosylation. The aim of this review is to detail the well-established mechanisms of redox regulation of Calvin-Benson cycle enzymes as well as the most recent reports indicating that this pathway is tightly controlled by multiple interconnected redox post-translational modifications. This redox control is likely allowing fine tuning of the Calvin-Benson cycle required for adaptation to varying environmental conditions, especially during responses to biotic and abiotic stresses.

The reversible depolymerization of spinach chloroplast glyceraldehyde-phosphate dehydrogenase. Interaction with nucleotides and dithiothreitol

The ligand-dependent dissociation of spinach chloroplast glyceraldehyde-phosphate dehydrogenase (Mr 600000) to protomers of Mr about 145000, previously shown by us in 1973, has been further characterized by the technique of velocity sedimentation in sucrose gradients. The process exhibits cooperativity and is accompanied by an increase of the apparent NADP+-dependent activity (reactivation) from a ratio of 0.1-0.2 to a ratio of 1 to 2 with respect to the NAD+-dependent activity. In addition to NADP+ and NADPH, most nucleotide triphosphates and, to some extent, Pi, act as dissociating agents. The enzyme is depolymerized and progressively inactivated in the presence of 2'-AMP. 2. Incubation with 20 mM dithiothreitol or 8-10 mM GTP increases the apparent NADP/H)-dependent activity, although addition of a small amount of a dissociating compound, such as 0.06 mM NADP+, is required for depolymerization. 3. NAD+, NADH and, to a lesser extent, glyceraldehyde 3-phosphate, NMN and cyclic AMP act as inhibitors of the dissociation and reactivation, however induced. They also favour the reassociation of protomers to tetramers. 4. The NADP(H)-linked activity is probably a property of the protomers only. The system described here resembles in many respects the light-dependent regulation of the NADP(H)-linked activity in vivo.

[The light-induced activation of NADP(+)-dependent glyceraldehyde-3-phosphate dehydrogenase : IX. The reaction in isolated chloroplasts]

1. A modification of an aqueous isolation procedure of chloroplasts is described. It results in chloroplast preparations of high purity and good maintenance of structure. 2. The activity of NADP-GPD is increased with the same kinetics by irradiance of isolated spinach chloroplasts as by irradiance of the intact organism. 3. Irradiance causes a decrease in NAD-GPD-activity in the isolated chloroplasts. The change in the turn-over rate (Δ A1 of NADP-GPD-increase: Δ A2 of NAD-GPD-decrease) is 5:1. This ratio is of the same order of magnitude as that obtained earlier by irradiance of whole Lemna gibba (Δ A1 : Δ A2 = 3,5 : 1). Evidence is given that the NAD-GPD in the cytoplasm is not influenced by light.

[The light-induced increase in the activity of NADP(+)-dependent glyceraldehyde-3-phosphate-dehydrogenase : VIII. The dependence of the enzyme activity in lemna on the intensity and the length of illumination]

1. A method for determination of the initial rate in enzymic non-linear progress reactions is described. 2. The relation between the increase in the activity of the NADP(+)-dependent glyceraldehyde-3-phosphate-dehydrogenase (GPD) and the different light intensities shows that Lemna gibba is adapted to high light intensities. 3. The time-curves for the increase in the activity of the enzyme in dependence on the different light intensities are similar to the corresponding curves for the intensity of photosynthesis. 4. The activity of the NAD(+)-dependent GPD in the extract decreases after preceding illumination of the plants; this activity is thus inverse to that of the NADP(+)-specific enzyme. There are indications (also in the literature) that the two enzymes are interconvertible.

[The light-induced increase in the activity of NADP(+)-dependent glyceraldehyde-3-phosphate-dehydrogenase : VII. Experiments with ceramium rubrum]

1. Tetrasporophytes as well as male and female gemetophytes of Ceramium rubrum show differences in the protein and pigment content, in the activity of the aldolase, and in the light-induced increase in the activity of the NADP(+)-dependent glyceraldehyde-3-phosphate-dehydrogenase (GPD). 2. A very high light intensity is necessary to diminish the increase of the GPD-activity; our Ceramium-material (from shallow water) thus behaves like a strong-light plant. 3. The activity of aldolase in the extract is not influenced by the preceding illumination of the algae. 4. The increase in activity of the NADP(+)-dependent GPD depends on the light quality in a similar way as the intensity of photosynthesis; the phycobilins are also effective as light acceptors in this case. 5. Certain wave-lengths were removed with "minus-filters" from a continuous spectrum (white light). Absence of red-light (663, 714 nm) had no influence on the activation of the enzyme, absence of green light (543, 492) diminished the activating effect, and absence of blue light (463 nm) increased it in comparison to the control (white light).

[The light-induced increase in the activity of NADP(+)-dependent glyceraldehyde-3-phosphate-dehydrogenase : V. Marine algae]

1. NADP(+)-dependent GPD was clearly active in 8 out of 13 Rhodophyta and in 5 out of 8 Phaeophyta tested. 2. NAD(+)-specific GPD was detectable in all of the 6 red algae analysed and in the 3 brown algae tested. 3. Aldolase-activity was found unequivocally in 8 out of 10 red algae and in 7 out of 8 brown algae. 4. It is concluded that the absence of these enzymes is not a characteristic for these groups of algae. 5. Light increases the activity of the NADP(+)-dependent GPD in species of Chlorophyta and Rhodophyta, and probably also in species of Phaeophyta.