On the specific binding of protochlorophyllide and chlorophyll to different peptide chains

Protochlorophyllide reduction: mechanisms and evolutions

Protochlorophyllide (Pchlide) reductases are key enzymes in the process of chlorophyll biosynthesis. In this review, current knowledge on the molecular organization, substrate specificity and assembly of the light-dependent reduced nicotinamide adenine dinucleotide phosphate:Pchlide oxidoreductases are discussed. Characteristics of light-independent enzymes are also described briefly, and the possible reasons for the selection of light-dependent enzymes during the course of evolution are discussed.

Contribution to the structural characterization of eucaryotic PSI reaction centre - II. Characterization of a highly purified photoactive SDS-CP1 complex

Under precise conditions, SDS PAGE† allows purification of a photoactive P700-chla-protein complex from eucaryotic cells. The yield of P700 recovery is close to 100%. A total protein content equivalent to about 140 kD for one mole of P700 has been estimated by chemical analysis, and electrophoresis revealed the presence of two peptidic chains with MWs close to 65 kD. Photochemical and structural properties of this complex are given and compared with those of other complexes previously isolated.

[Photosynthetic activity in the absence of CPl and CP2 pigmentary complexes (author's transl)]

Various photochemical activities were tested on chloroplasts of Zea mays that received 4 s of light every 4 h during the culture period. Photosystem I and Photosystem II were functioning, as well as the photosynthetic electron transport. These chloroplasts exhibited upon sodium dodecyl sulphate gel electrophoresis neither Complex 1 (Mr 70 000) generally associated with Photosystem I nor Complex 2 Mr 25 000) generally associated with Photosystem II. Chlorophyll is indeed attached to polypeptides of molecular weight 21 000 and 29 000. These results lead us to question the functional role of chloroplast protein-pigment complexes observed by sodium dodecyl sulphate gel electrophoresis.

Incorporation of 5-Aminolevulinic Acid in the Chlorophyll-Protein Complexes of the Moss Ceratodon purpureus

After one month of cultivation in the dark in inorganic medium the chloroplasts of protonemata of Ceratodon purpureus have larger grana than chloroplasts from light-grown cultures. Incubation of dark-grown material with ALA increases the chlorophyll content and chlorophyll a/b ratio. On polyacrylamide-gel electrophoresis, a préferential labelling of chlorophyll-protein complex I is obtained after treatment with (³ H) ALA in darkness. In contrast, in light, much higher activity is found in chlorophyll-protein complex II. The free pigment zone is highly labelled in both environments.

Structure and morphogenesis of photosynthetic membranes. I. Is there a single basic peptide within Zea mays thylakoids?

We have previously given evidence for a physical heterogeneity among proteins from photosynthetic membranes of maize chloroplast [1]. About fifteen components have now been identified, differing in their molecular weights and also in their varying abilities to bind protochlorophyllide and chlorophyll [2]. In this paper, we show that all these proteins have very similar amino acid compositions. A detailed chemical comparison is made between, on one hand the mixture of all proteins and on the other the smallest component of molecular weight 10 000. All the features analysed (percent of non-proteic material, partial peptide maps, N and Cterminal ends and content of linked sugars) are the same in both cases. We conclude from these experiments that it is likely that all components are generated with the same basic peptide unit. This assertion seems to be confirmed by the fact that, after mild alkaline treatment, all the components are converted into the smallest one, as seen by electrophoresis. Thus, within the photosynthesizing membranes, there appears to be a basic structural protein unit, present in a form that is more or less "polymerized". This may account for most of the particular, and sometimes disturbing, properties so far described for this system. It is likely that such a peptide, or a similar one, would provide a framework for all photosynthesizing structures.

[Independence of special forms of chloeophyll a and chlorophyll holochromes]

Zea mays L. seedlings were cultivated for 10 days with submission to 4 s illumination periods interspersed with dark periods varying in length from 30 min to 6 h depending on the lot analyzed. The results show that, for the case in which the dark periods were shorter than 1 h, the relative proportions of different spectroscopic chlorophyll forms (maxima at 662, 670, 677.5, and 684 nm) were constant. For longer durations of darkness between illuminations, the relative proportion of the form Da670 increases, while that of Ca684 diminishes with the length of darkness; to a lesser extent, the relative proportion of Ca662 increases and a form Ca692 disappears. A scheme is proposed to explain the evolution of the relative proportions of the different spectral forms. The different chlorophyll holochromes present in the chloroplasts were also analysed. If the dark period was longer than 1 h, chlorophyll was associated with peptide chains of molecular weights 21 000 and 29 000. If the dark period was shorter than 1 h chlorophyll was associated with four peptide chains of molecular weights 21 000, 25 000, 29 000 and 70 000. The results taken together demonstrate that a given spectral chlorophyll a form cannot be associated with a definite chlorophyll holochrome.

Developmental changes in the surface properties of chloroplast membranes

When the surface properties of etioplast and etiochloroplast membranes from dark grown or variously illuminated leaves of Avena sativa L. are examined by counter current distribution in a Dextran: poly(ethylene-glycol) two-phase system the results may be summarized as follows: (i) Etioplast membranes consist of two main classes with respect to upper phase poly(ethylene-glycol) affinity. (ii) Shortly after illumination the proportion of higher affinity membranes increases and the upper phase affinity of this class also increases. (iii) Further illumination reverses this effect producing a single class of membranes with the high affinity for the lower phase characteristic of membranes of the mature chloroplast. (iv) In rapidly greening leaves (6-9 h illumination) and intermediate class is observed which may represent an intermediate stage in biogenesis. The interpretation of these results is discussed in terms of changes in membrane surface reaction and potential.