Light modulation of glucose-6-phosphate dehydrogenase: partial characterization of the light inactivation system and its effects on the properties of the chloroplastic and cytoplasmic forms of the enzyme.

Light inactivation of glucose-6-phosphate dehydrogenase within the pea (Pisum sativum L.) leaf chloroplast has a narrow pH optimum between 7.2 and 7.4 and is NADP-sensitive. The pH optimum for dark activation is slightly lower. Inactivation apparently results in a simple decrease in maximal velocity of the chloroplastic and cytoplasmic forms of the enzyme with no concomitant change in pH optimum or K(m) (glucose 6-phosphate).

Light-regulation of enzyme activity in anacystis nidulans (Richt.).

The effect of light on the levels of activity of six enzymes which are light-modulated in higher plants was examined in the photosynthetic procaryot Anacystis nidulans. Ribulose-5-phosphate kinase (EC 2.7.1.19) was found to be light-activated in vivo and dithiothreitol-activated in vitro while glucose-6-phosphate dehydrogenase (EC 1.1.1.49) was light-inactivated and dithiothreitol-inactivated. The enzymes fructose-1,6-diphosphate phosphatase (EC 3.1.3.11), sedoheptulose-1,7-diphosphate phosphatase, NAD- and NADP-linked glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12; EC 1.2.1.13) were not affected by light treatment of the intact algae, but sedoheptulose-diphosphate phosphatase and the glyceraldehyde-3-phosphate dehydrogenases were dithiothreitol-activated in crude extracts. Light apparently controls the activity of the reductive and oxidative pentose phosphate pathway in this photosynthetic procaryot as in higher plants, through a process which probably involves reductive modulation of enzyme activity.

Chloroplast biogenesis. Identification of chlorophyllide a (E458f674) as a divinyl chlorophyllide a.

The chemical identification of chlorophyllide (E458F674) (Belanger, F. C., and Rebeiz, C. A. (1980) Plant Sci. Lett. 18, 343-350) has been confirmed by chemical derivatization coupled to spectrofluorometric, spectrophotometric, and chromatographic analysis. Chlorophyllide (E458F674) and its demetallated analog were converted by catalytic hydrogenation into mesochlorophyllide a and mesopheophorbide a. Furthermore, methyl chlorophyllide (E458F674) was converted by partial hydrogenation into a mixture of monovinyl chlorophyllide a isomers and the latter into mesochlorophyllide a by further hydrogenation. On the other hand, chemical oxidation of methyl chlorophyllide (E458F674) converted it into methyl divinyl protochlorophyllide. Chlorophyllide (E458F674) was detected in several plant species and is proposed to be an important intermediate of the chlorophyll a biosynthetic pathway.

Catabolism of [1-C]levulinic Acid by etiolated and greening barley leaves.

Levulinic acid (LA), a competitive inhibitor of delta-aminolevulinic acid (ALA) dehydratase (EC 4.2.1.24), has been used extensively in the study of ALA formation during greening. When [1-(14)C]LA is administered to etiolated barley (Hordeum vulgare L. var. Larker) shoots in darkness, (14)CO(2) is evolved. This process is accelerated when such tissues are incubated with 2 millimolar ALA or placed under continuous illumination. Label from the C-1 of LA becomes incorporated into organic acids, amino acids, sugars, lipids, and proteins during a 4-hour incubation in darkness or in the light. This metabolism is discussed in relation to the use of LA as a tool in the study of chlorophyll synthesis in higher plants.

Catabolism of 5-Aminolevulinic Acid to CO(2) by Etiolated Barley Leaves.

The in vivo oxidation of the C(4) and C(5) of 5-aminolevulinic acid (ALA) to CO(2) has been studied in etiolated barley (Hordeum vulgare L. var. Larker) leaves in darkness. The rate of (14)CO(2) evolution from leaves fed [4-(14)C]ALA is strongly inhibited by aminooxyacetate, anaerobiosis, and malonate. The rate of (14)CO(2) evolution from leaves fed [5-(14)C]ALA is also inhibited by these treatments but to a lesser extent. These results suggest that (a) one step in ALA catabolism is a transamination reaction and (b) the C(4) is oxidized to CO(2) via the tricarboxylic acid cycle to a greater extent than is the C(5).

Catabolism of porphobilinogen by etiolated barley leaves.

When [2,4-(14)C]porphobilinogen (PBG) or [2 (aminomethyl),5-(14)C]PBG is administered to etiolated barley (Hordeum vulgare L. var. Larker) leaves in darkness, label becomes incorporated into CO(2), organic and amino acids, sugars, lipids, and proteins during a 4-hour incubation. Less than 1% of the label, however, is incorporated into porphyrins. The rate of (14)CO(2) evolution from leaves fed [2,4-(14)C]PBG is strongly inhibited by anaerobiosis but is unaffected by aminooxyacetic acid, while the rate of (14)CO(2) evolution from [2(aminomethyl),5-(14)C]PBG is strongly inhibited by aminooxyacetic acid but is not affected by anaerobiosis.THESE RESULTS SUGGEST THAT: (a) exogenous PBG is taken up and metabolized by etiolated barley leaves; (b) PBG is not metabolized exclusively to porphyrins but can be converted to a variety of intermediary metabolites; (c) this metabolism involves reactions which are partially dependent upon O(2) and pyridoxal phosphate.