Characterization of a protein-kinase activity associated with phytochrome from etiolated oat (Avena sativa L.) seedlings

A protein-kinase activity which is co-purified with phytochrome from etiolated oat seedlings was investigated in some detail. Whereas phytochrome was always phosphorylated in solution (together with some contaminating protein bands), radioactive phosphate was not found in the phytochrome band after native gel electrophoresis and incubation of the entire gel with labeled ATP. Since protein kinases are usually autophosphorylated under these conditions, the result shows that the kinase activity does not reside in the phytochrome molecule itself. Radioactivity was exclusively detected in a band with the apparent molecular weight 450 kDa; sodium-dodecyl-sulfate gel electrophoresis revealed an apparent molecular weight of 60 kDa for the phosphorylated subunit. The N-terminal amino-acid sequence A L E S A (G) K Q (L) V P W was determined for this subunit which is a potential candidate for the protein kinase. The optimum conditions (pH, metal ion concentration) and kinetics of the phosphorylation reaction were determined. The presumed connection between proteinkinase activity and the signal chain leading from the far-red-absorbing form of phytochrome to physiological responses still awaits elucidation.

Phytochrome - all regions marked by a set of monoclonal antibodies reflect conformational changes

Monoclonal antibodies to defined locations on six regions of the phytochrome molecule (from Avena sativa L. or Zea mays L.) were each found to have a different affinity toward the farred-absorbing form of phytochrome (Pfr) and the red-absorbing form (Pr). The differences were small, but were consistently shown by antibodies which bind to the vicinity of the aminoterminus, the carboxylterminus and to sequences in between. It seems that the conformational differences between Pr and Pfr extend over the whole molecule in as far as it is represented by these regions and the antibodies binding to them.

Sequence analysis of proteolytic fragments of 124-kilodalton phytochrome from etiolatedAvena sativa L.: Conclusions on the conformation of the native protein

Proteolytic fragments were obtained by limited proteolysis of 124-kDa (kilodalton) phytochrome from etiolatedAvena sativa using trypsin, endoproteinase-Lys-C, endoproteinase-Glu-C and subtilisin. The fragments were separated by sodium dodecyl sulfate gel electrophoresis, blotted onto activated glass-fiber sheets and investigated by amino-acid sequencing in a gas-phase sequencer. Determination of N-terminal sequences in three to six Edman degradation steps allowed the exact localization of the fragments within the published entire amino-acid sequence of 124-kDaAvena phytochrome (H.P. Hershey, R.F. Barker, K.B. Idler, J.L. Lissemore, P.H. Quail (1985), Nucleic Acids Res.13, 8543-8559). From the knowledge of the exact sites for preferred proteolytic cleavage of undenatured phytochrome, conclusions on the conformation of the phytochrome protein were drawn. Sites of preferred cleavage are considered to be freely exposed to the environment whereas potential cleavage sites which are resistant to proteolysis over a long time are considered to be localized in the interior of the native phytochrome. Two different sites which are exposed in the far-red-absorbing form but not in the red-absorbing form of phytochrome are localized at amino-acid residues 354 and 753, respectively. The N-terminal region which is exposed only in the red-absorbing form stretches only as far as amino-acid residue 60.

Cross-reactivity of monoclonal antibodies against phytochrome from Zea and Avena : Localization of epitopes, and an epitope common to monocotyledons, dicotyledons, ferns, mosses, and a liverwort

The cross-reactivity of diverse monoclonal antibodies against phytochrome from Zea and Avena was tested by enzyme-linked immunosorbentassay (ELISA) and by immunoblotting. About 40 antibodies were selected by means of nondenatured phytochrome; all of them reacted with sodium dodecyl sulfate denatured homologous antigen on immunoblots. The epitopes for 14 antibodies (4 raised against Avena and 10 against Zea phytochrome) were localized in 6 regions of the phytochrome molecule by means of Western blot analysis of proteolytic fragments of known localization. Results of studies on the inhibition of antibody binding by other antibodies were largely compatible with these latter findings. Except in a few cases, inhibition occurred when antibodies were located on the same or a closely adjacent region. As demonstrated by 16 species, cross-reactivity with phytochromes from other Poaceae was high. Greater losses in cross-reactivity were observed only with antibodies recognizing an epitope in the vicinity of the carboxyl terminus of 118-kg · mol(-1) phytochrome. Cross-reactivity with phytochrome from dicotyledons was restricted to a few antibodies. However, phytochrome(s) from plants illuminated for 24 h or more could be detected. One of the antibodies that recognized phytochrome from dicotyledons was also found to recognize phytochrome or a protein of 120-125 kg·mol(-1) from several ferns, a liverwort and mosses. This antibody (Z-3B1), which was localized within a 23.5-kg·mol(-1) section of Avena phytochrome (Grimm et al., 1986, Z. Naturforsch. 41c, 993), seems to be the first antibody raised against phytochrome from a monocotyledon with such a wide range of reactivity. Even though epitopes were recognized on different phytochromes, the strength of antibody binding indicated that these epitopes are not necessarily wholly identical.

Behaviourally dependent modulation of lateral geniculate unit activity in the freely moving cat

In 120 neurons of the cat's dorsal lateral geniculate body (dLGB), spontaneous and light-evoked activity was analysed in order to obtain further information on firing characteristics during different behavioural states (quietly sitting, locomotion). Experiments were carried out in freely moving cats, using wireless methods for simultaneous registration of single unit activity and locomotion. During locomotion, an enhancement of neuronal single and pool activity was observed. During locomotor activity, flash-evoked responses were modulated, an increase of response amplitude and a decrease of peak latency in the peristimulus time histogram occurred. The results demonstrate a facilitatory influence on spontaneous and light-evoked activity of dLGB neurones during locomotion. They suggest a non-visual phasic modulation of retino-geniculo-cortical information transfer.

ZZE -Configuration of Chromophore β-153 in C-Phycocyanin from Mastigocladus laminosus

The photochemistry of C-phycocyanin has been studied after denaturation in the dark. It shows an irreversible reaction which has characteristics of a Z, Z, E- to Z, Z, Z-isomerization of dihydrobilins. Its amplitude depends on the reaction conditions, with a maximum corresponding to 15% conversion of one of the three PC chromophores. This chromophore is suggested to be β-153, for which recent X-ray data T. Schirmer, W. Bode, and R. Huber, J. Mol. Biol., submitted, show ring D being highly twisted out of the plane of the other rings. During unfolding, there is thus a probability of falling into the photochemically labile Z, Z, E-configuration.

The complete amino-acid sequence of C-phycoerythrin from the cyanobacterium Fremyella diplosiphon

The amino-acid sequences of both subunits of C-phycoerythrin from the cyanobacterium Fremyella diplosiphon have been determined. The alpha-subunit contains 164 amino acid residues, two phycoerythrobilin (PEB) chromophores and has a molecular mass of 18,368 Da (protein: 17,192 Da + 2 PEB, one PEB accounting for 588 Da). The beta-subunit consists of 184 residues, three PEB chromophores and has a molecular mass of 20,931 Da (protein: 19,168 Da and 3 PEB: 1,764 Da). The five PEB chromophores (open chain tetrapyrroles) are covalently bound to six cysteine residues (one of them doubly bound to two cysteine residues). On the alpha-subunit, the first chromophore was found at position 84, homologous to the chromophore binding site of the other biliproteins APC, PC and PEC. The second chromophore, unique for the alpha-subunit of PE, is inserted together with a pentapeptide at position 143 a. On the beta-subunit, a doubly bound chromophore is attached to cysteine residues 50 and 61, similar to the rhodophytan phycoerythrins (B-PE and R-PE). The second and third chromophores were found at positions 84 and 155, homologous to the other biliproteins. A unique peptide insertion of 14 amino acid residues (without chromophore) was found at position 141 a-o in the beta-subunit and probably is located in the three-dimensional model near the additional chromophores of the C-PE alpha- and beta-subunits. Both additional chromophores of the C-PE alpha- and beta-subunit may be located at the periphery of the C-PE-trimer. The amino-acid sequence homology between C-PE alpha- and beta-subunit is 26% and to the alpha- and beta-subunits of C-PC from Mastigocladus laminosus 49% and 48%, respectively.

Degradation of Bacteriochlorophyll a in Rhodopseudomonas sphaeroides R26

A series of pigments of the bacteriopheophytin a spectral type have been isolated from ageing cultures of Rhodopseudomonas sphaeroides strain R26. These pigments are formed in varying amounts, and can be most readily analyzed in vivo by their absorption in the 530 nm spectral range. They are enriched in sedimenting cells, but their formation is not affected by light. By chromatographic comparison with authentic pigments and chemical correlation, the following pigments have been identified: bacteriopheophytin a, bacteriopheophorbide a (which is the predominant product), pyrobacteriopheophorbide a and a fourth, very polar bacteriopheophytin a-type product of unknown structure. The major portion of these newly formed pigments is present in the cells in a state, in which the near-infrared absorption band is shifted to longer wavelengths. As shown by low temperature fluorescence spectroscopy, these forms are very similar to bacteriopheophorbide a aggregates.

Incorporation of phytol precursors into chlorophylls of tobacco cell cultures

The incorporation of [1-(3)H] geranylgeranyl diphosphate (GGPP), [1-(3)H] geranylgeranyl monophosphate (GGMP) and [U-(14)C] phytyl diphosphate (PhPP) into chlorophylls a and b in growing tobacco cell cultures was investigated. The substrates were effectively incorporated into chlorophylls a and b, 3.2% of the total activity of applied GGPP or GGMP and 12.4% of the total activity of applied PhPP being found in chlorophylls a and b after 24 h incubation. The radioactivity was found in phytyl chlorophyllide through-out which means effective hydrogenation of the alcohol moiety in the case of GGPP and GGMP. With increasing substrate concentration, the specific radioactivity of chlorophyll increased up to a saturation level which was reached either at 20-40 μM PhPP or at 60 μM GGPP and GGMP. The specific radioactivity of the chlorophyll formed during the 24-h incubation period was the same as that of the applied substrate at saturating substrate concentration. The specific radioactivity of chlorophyll a was higher than that of chlorophyll b only in the case of PhPP.

Hydrogenation of geranylgeraniol : two pathways exist in spinach chloroplasts

The reduction of geranylgeranylpyrophosphate to phytylpyrophosphate in spinach chloroplasts is described for the first time. The reductase is localized in the chloroplast envelope. By contrast, the reduction of the geranylgeranyl moiety in Chl synthesis is catalyzed in the thylakoids (via Chl synthetase). NADPH functions as electron donor in both reactions. Chl synthetase is firmly bound to the thylakoid membranes, and very little activity is found in the stroma fraction. Chl synthetase in chloroplasts can use the pyrophosphate ester of either phytol, geranylgeraniol, or farnesol, phytylpyrophosphate being the preferred substrate. Exogenous Chlide exhibits no influence on Chl synthesis by chloroplast subfractions.

Incorporation of haem into phycocyanobilin in levulinic acid treated Cyanidium caldarium

Cells of the red alga Cyanidium caldarium were preincubated with 5 mmol 1(-1) levulinic acid (LA) and subsequently incubated with (14)C-labelled haem (5.67 Bq nmol(-1)). Phycocyanin was isolated. The specific radio-activity of its chromophore phycocyanobilin (PCB) was determined after cleavage and purification by thin layer chromatography. The percentage of PCB formed from labelled haem within 0.5 h was considerably higher in LA treated cells than in non-treated controls. This difference disappeared after prolonged incubation (16.5 h) with haem. The results are interpreted as possible incorporation of haem into preexisting apoprotein.

Chlorophyll biosynthesis by mesophyll protoplasts and plastids from etiolated oat (Avena sativa L.) leaves

The uptake of [1-(3)H]geranylgeranyl diphosphate (GGPP) into protoplasts and intact etioplasts and the metabolic interconversion therein was studied after a 2 min pulse of white light. The chlorophyll synthetase reaction, Chlide+GGPP→ChlGG, was taken as a natural probe for the etioplast compartment. This reaction yields labeled ChLGG and, by hydrogenation, labeled ChlP, when [1-(3)H]GGPP receives access to the etioplast stroma. It was found that penetration across the plastid envelope was rapid and that penetration across the plasma membrane of protoplasts, however, was slow. A cellular pool of soluble GGPP was detected. This pool was lost, in part, during preparation of the protoplasts and almost completely during preparation of the etioplasts. The membrane-bound phytol pool of etioplasts could not be replaced by exogenous [(3)H]GG. The endogenous GG and phytol pools of protoplasts, which were larger than those of etioplasts, could be replaced in part by exogenous [(3)H]GGPP. That part of this pool exists as soluble GGPP or as a direct precursor in the cytoplasm is discussed.

Influence of Anaerobiosis on Chlorophyll Biosynthesis in Greening Oat Seedlings (Avena sativa L.)

The influence of anaerobiosis for 0.5 to 15 hours on the last steps of chlorophyll biosynthesis of etiolated oat seedlings was investigated. Phototransformation of protochlorophyllide to chlorophyllide is only slightly reduced and esterification of chlorophyllide is slightly increased by pretreatment under anaerobic conditions. Pretreated plants accumulate the geranylgeraniol ester of chlorophyllide rather than the phytol ester. Enzymic hydrogenation of the esterifying alcohol geranylgeraniol to phytol is presumably inhibited by anaerobiosis.

Detection and partial characterization of activity of chlorophyll synthetase in etioplast membranes

The esterification of chlorophyllide a was investigated an irradiated etioplast-membrane fractions ('broken etioplasts') from oat seedlings (Avena sativa L.). As a substrate, [1(-3)H]geranylgeraniol and its monophosphate and diphosphate derivatives were prepared by chemical synthesis. Geranylgeraniol and its monphosphate derivative are incorporated into chlorophyll only in the presence of ATP whereas the diphosphate derivative is incorporated also without ATP. The yield of esterified chlorophyll is 80-90% of chlorophyllide with saturating substrate concentrations. The term 'chlorophyll synthetase' is used to describe the enzyme activity which is different from chlorophyllase. Other substrates are phytol and farnesol either with ATP or as the diphosphate derivatives. The relative specificity of 'chlorophyll synthetase' for thse substrates is geranylgeraniol:phytol:farnesol = 6:3:1. In these experiments in vitro, a new chlorphyll esterified with farnesol was detected which does not occur in intact plants. Geraniol and n-pentadecanol are no substrates for the enzyme. Protochlorphyllide which is present in non-irradiated etioplast membrane fractions is not esterified under the same conditions.

On the linkages between chromophore and protein in biliproteins, VII. Amino acid sequence in the chromophore regions of C-phycoerythrin from Pseudanabaena W 1173 and Phormidium persicinum

Bilipeptides from all chromophore regions were prepared by trypsin digestion of C-phycoerythrin from Pseudanabaena W 1173 and Phormidium persicinum. Analytical separation and quantitative determination of bilipeptides was achieved by isoelectric focusing, preparative isolation by gel chromatography and ion-exchange chromatography. Amino acid analysis revealed cysteine as the only amino acid common to all chromopeptides. Amino acid sequences were determined by Edman degradation and the dansyl-Edman technique. Sequences are different in all 5 and 6 chromophore regions, respectively. Possible homologies are discussed. A thioether linkage between ring A of the chromophore and cysteine was found in the bilipeptides (as before in biliproteins). A second linkage (serine ester) was found in only one peptide (CM 4.I from Pseudanabaena W 1173). This peptide absorbs as cation at a longer wavelength (559 nm) than the other bilipeptides (542 - 550 nm).

Destruction and possible de novo synthesis of phytochrome in subcellular fractions of laminae from Avena sativa L

Phytochrome was determined in etiolated laminae of Avena sativaL. either without pretreatment or after 5 min of red irradiation followed by different periods of darkness (0-24 h). At given intervals laminae were homogenized and phytochrome was determined spectrophotometrically in the total homogenate and in purified etioplasts and mitochondria. Enhanced specific activity of phytochrome was found in all fractions after the irradiation in comparison to dark controls. Phytochrome destruction was observed in all fractions at the beginning of the subsequent dark period. Whereas the homogenate and the mitochondrial fraction showed a continuous destruction so that phytochrome reached a level far below that in etiolated plants, the phytochrome level in the plastid fraction reacheda minimum at 2 h with a subsequent increase beyond the dark level. This increase was most pronounced between 4 and 8 h after the red irradiation. The results are discussed in terms of the destruction and possible de novo synthesis of phytochrome that may be different in mitochondria and plastids.

Chromophore content of C-phycoerythrin from various Cyanobacteria

The molar extinction coefficient for phycoerythrobilin (l a) was calculated by two independent methods. It is different from that of the cleaved chromophore, phycobiliviolin (2). By unfolding with urea or tryptic digestion, the chromophore absorption of C-phycoerythrin (PE) was determined free of any protein influence. The chromophore content of PE from various Cyanobacteria was determined with these data to be either 5 or 6, depending on the organism. This corresponds to a chromophore distribution over phycoerythrin subunits alpha:beta of either 2:3 or 2:4. The phylogenetic significance of varying chromophore content is discussed.