Type I photosynthetic reaction centres

We review recent advances in the study of the photosystem I reaction centre, following the determination of a spectacular 2.5 Å resolution crystal structure for this complex of Synechococcus elongatus . Photosystem I is proving different to type II reaction centres in structure and organization, and the mechanism of transmembrane electron transfer, and is providing insights into the control of function in reaction centres that operate at very low redox potentials. The photosystem I complex of oxygenic organisms has a counterpart in non–oxygenic bacteria, the strictly anaerobic phototrophic green sulphur bacteria and heliobacteria. The most distinctive feature of these type I reaction centres is that they contain two copies of a large core polypeptide (i.e. a homodimer), rather than a heterodimeric arrangement of two related, but different, polypeptides as in the photosystem I complex. To compare the structural organization of the two forms of type I reaction centre, we have modelled the structure of the central region of the reaction centre from green sulphur bacteria, using sequence alignments and the structural coordinates of the S. elongatus Photosystem I complex. The outcome of these modelling studies is described, concentrating on regions of the type I reaction centre where important structure–function relationships have been demonstrated or inferred.

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Evolution of photochemical reaction centres: more twists?

10.1101/502450 ◽

2018 ◽

Cited By ~ 1

Author(s):

Tanai Cardona ◽

A. William Rutherford

Keyword(s):

Water Oxidation ◽

Transmembrane Helix ◽

Structural Rearrangement ◽

Type I ◽

Reaction Centre ◽

Type Ii ◽

Reaction Centres ◽

Acceptor Side ◽

Oxidation Chemistry ◽

Evolution Of Photosynthesis

The earliest event recorded in the molecular evolution of photosynthesis is the structural and functional specialisation of Type I (ferredoxin-reducing) and Type II (quinone-reducing) reaction centres. Here we point out that the homodimeric Type I reaction centre of Heliobacteria has a Ca2+-binding site with a number of striking parallels to the Mn4CaO5 cluster of cyanobacterial Photosystem II. This structural parallels indicate that water oxidation chemistry originated at the divergence of Type I and Type II reaction centres. We suggests that this divergence was triggered by a structural rearrangement of a core transmembrane helix resulting in a shift of the redox potential of the electron donor side and electron acceptor side at the same time and in the same redox direction.

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Heat-Etching with a Bullivant Type II Simple Freeze-Cleave Device

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100067522 ◽

1970 ◽

Vol 28 ◽

pp. 106-107 ◽

Cited By ~ 1

Author(s):

Ronald S. Weinstein ◽

N. Scott McNutt

Keyword(s):

New Zealand ◽

General Hospital ◽

Massachusetts General Hospital ◽

Type I ◽

Type Ii ◽

Collaborative Effort ◽

Temperature And Pressure ◽

The University

The Type I simple cold block device was described by Bullivant and Ames in 1966 and represented the product of the first successful effort to simplify the equipment required to do sophisticated freeze-cleave techniques. Bullivant, Weinstein and Someda described the Type II device which is a modification of the Type I device and was developed as a collaborative effort at the Massachusetts General Hospital and the University of Auckland, New Zealand. The modifications reduced specimen contamination and provided controlled specimen warming for heat-etching of fracture faces. We have now tested the Mass. General Hospital version of the Type II device (called the “Type II-MGH device”) on a wide variety of biological specimens and have established temperature and pressure curves for routine heat-etching with the device.

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Two Distinct Types of Microfilaments in the Cytoplasm of Human Adenohypophysial Cells

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100073787 ◽

1973 ◽

Vol 31 ◽

pp. 668-669

Author(s):

E. Horvath ◽

K. Kovacs ◽

I. E. Stratmann ◽

C. Ezrin

Keyword(s):

Pituitary Tumors ◽

Average Diameter ◽

Anterior Lobe ◽

Uranyl Acetate ◽

Type I ◽

Breast Cancer Patients ◽

Human Pituitary ◽

Severe Diabetes ◽

Pituitary Glands ◽

Membrane Bound

Surgically removed human pituitary glands as well as pituitary tumors fixed in glutaraldehyde, postfixed in osmium tetroxide, embedded in epon resin, stained with uranyl acetate and lead citrate have been investigated by electron microscopy in order to correlate ultrastructure with functional activity. In the course of this study two distinct types of microfilaments have been identified in the cytoplasm of adenohypophysiocytes.Type I microfilaments (Fig. 1) were found in the cytoplasm of anterior lobe cells of five female subjects with disseminated mammary cancer and two patients with severe diabetes mellitus. The breast cancer patients were treated pre-operatively for various periods of time with different doses of oxysteroids. The microfilaments had an average diameter of JO A, formed parallel bundles, were scattered irregularly in the cytoplasm and were frequently located in the perikaryon. They were not membrane-bound and failed to show any periodicity.

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