The absorption and circular dichroism (CD) spectra of allophycocyanin II in the trimer and monomer (dissociated) forms were resolved into four and two components, respectively. The short-wavelength region of the visible spectra was approximated by a chimera of Lorentzian- and Gaussian-shaped bands having a bandwidth of ca. 65 nm. The rest of the bands have a pure Gaussian form. The characteristic 652-nm band in the absorption spectrum (656 nm in the CD spectrum) is shown to arise from exciton interaction between two fluorescent phycocyanobilin chromophores.

Allophycocyanin, which is normally isolated as a trimer (alpha 3 beta 3), has now been successfully dissociated into a monomer (alpha beta) with strikingly different spectroscopic properties. In particular, upon dissociation the characteristic 650-nm absorption and 661-nm fluorescence emission bands of the trimer are completely lost and its fluorescence polarization properties are sharply altered. The spectroscopic characteristics of allophycocyanin monomers are much closer to those of C-phycocyanin than to trimeric allophycocyanin. A model for trimeric allophyocyanin is presented in which the appearance of the 650-nm absorption band is induced by a particular kind of chromophore-chromophore interaction. Similar results are found for both allophycocyanin II and III.

No abstract

No abstract

The metal ion-induced inhibition of tetrapyrrole biosynthesis was studied in the cyanobacterium Anacystis nidulans. The accumulation of protoporphyrin and Mg protoporphyrin due to the effect of Co2' and Mn2+ treatment, respectively, pointed to two different sites of inhibition.Chlorophyll biosynthesis is inhibited by iron deficiency induced by a number of metals (1)-cobalt and manganese in particular. The mechanism is considered to be competition for an active site where iron is necessary for functional integrity. The photosynthetic pigment apparatus of blue-green algae contains both chlorophyll and phycobiliproteins. The chromophore of the latter is also a tetrapyrrole, albeit a linear one (2). After nitrate starvation the blue-green algae are capable of regenerating their pigment apparatus, and in the process, several fluorescent tetrapyrroles, intermediates in tetrapyrrole biosynthesis, are detectable (3).In the present paper we show that manganese and cobalt, both inhibitors of chlorophyll biosynthesis, are acting at different stages of tetrapyrrole biosynthesis, and we shall identify the steps in biosynthesis where inhibition occurs. METHODSAnacystis nidulans (strain IU 625) was maintained on agar slants enriched with medium C of Kratz and Myers (4) and illuminated by fluorescent tubes (3,000 lux). When maintained in liquid medium C, the cells were grown in glass tubes at 38°C with an illumination of 10,000 lux and were supplied with 95% air/5% CO2. Nitrate starvation was induced by suspending the algal cells in nitrate-deficient culture medium. For regeneration experiments, the cells were collected and resuspended in whole medium C.Fluorescence measurements were carried out using a Perkin Elmer MPF 3 spectrofluorimeter. Both excitation and observation slits were set at 6-nm bandwidth. Fluorescence spectra were not corrected for the spectral sensitivity of the apparatus because only relative changes in fluorescence are discussed.Absorption spectra were recorded by a UNICAM SP 1800 UV spectrophotometer, using the opal glass method of Shibata et al. (5). Phycocyanin/chlorophyll ratios were calculated from the in vivo absorption spectra (6).Pigment Extraction. A 3-ml algal suspension was mixed with 15 ml of acetone/0.1 M NH4 OH, (9:1 (vol/vol) at 0°Cand centrifuged at 39,000 x g for 10 min (7). The supernatant was extracted once with 10 ml and twice with 5 ml of n- This final ether phase was concentrated under N2.All procedures were carried out in the dark. Chromatography. The pigments were separated by chromatography on thin layers (20 x 20 cm) of silica gel (Merck).The plates were developed in benzene/ethyl acetate/ethanol, 8:2:2 (vol/vol) at 40C in the dark. Pigment bands were located by their red fluorescence under UV light. The bands were scraped from the plates, pigments were eluted from the silica gel with methanol/acetone (4:1), and the fluorescence spectra were recorded.The extracted pigments were identified by comparing them to porphyrin standards (Porphyrin Products, Logan, UT) both during c...