Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Photosynthetic Reactions by Lysed Protoplasts and Particle Preparations from the Blue-Green Alga, Phormidium luridum

John Biggins
Plant Physiology
Vol. 42, No. 10 (Oct., 1967), pp. 1447-1456
Stable URL: http://www.jstor.org/stable/4261176
Page Count: 10
  • Read Online (Free)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Photosynthetic Reactions by Lysed Protoplasts and Particle Preparations from the Blue-Green Alga, Phormidium luridum
Preview not available

Abstract

Reactions of photosynthetic electron transport and photophosphorylation were studied in preparations from the blue-green alga, Phormidium luridum. Osmotic lysis of protoplasts proved to be a superior technique for the production of cell-free preparations with high enzymatic activity. Such lysed protoplasts sustain high rates of photophosphorylation coupled to the photo-reduction of NADP+ or ferricyanide. $\text{P}/2\text{e}^{-}$ ratios close to unity were routinely observed. The same preparations, and also those prepared by grinding the cells in solutions containing sucrose or ethylene glycol, are active in cyclic photophosphorylation mediated by phenazine methosulfate or dichlorophenolindophenol. The particles prepared by grinding the cells are, however, inactive in non-cyclic photophosphorylation. Extensive washing of the membranes with solutions containing sucrose removes the majority of the residual soluble fraction of the algal cell which includes cytochromes $\text{C}_{554}$ and $\text{C}_{549}$ and phycocyanin. Cyclic photophosphorylation activity is unimpaired by this treatment, but is abolished when the membranes are washed with very dilute buffers. This activity is restored by the addition of a soluble protein which is not a known redox constituent such as cytochrome $\text{C}_{554}$ or plastocyanin, and may be a coupling factor. Analysis of the well-washed membranes by low temperature (77°K) difference spectrophotometry reveals the presence of cytochrome $\text{b}_{6}$ and a bound form of cytochrome $\text{C}_{554}$ in proportions similar to that found in higher plant chloroplasts. The concentration of the membrane-bound cytochrome $\text{C}_{554}$, relative to cytochrome $\text{b}_{6}$ is not altered by extensive washing, sonication or treatment with 1% digitonin. This indicates that this cytochrome is an integral component of the cytoplasmic lamellae and we suggest that it is of functional significance. The soluble form of cytochrome $\text{C}_{554}$, which is present in concentrations about 3-fold higher than the bound form, depending upon growth conditions, is not essential for cyclic photophosphorylation. The concentration of cytochrome $\text{b}_{6}$: chlorophyll a was found to be 1:500. Under the conditions employed, we were unable to detect a bound form of the low potential cytochrome $\text{C}_{549}$.

Page Thumbnails

  • Thumbnail: Page 
1447
    1447
  • Thumbnail: Page 
1448
    1448
  • Thumbnail: Page 
1449
    1449
  • Thumbnail: Page 
1450
    1450
  • Thumbnail: Page 
1451
    1451
  • Thumbnail: Page 
1452
    1452
  • Thumbnail: Page 
1453
    1453
  • Thumbnail: Page 
1454
    1454
  • Thumbnail: Page 
1455
    1455
  • Thumbnail: Page 
1456
    1456