Electron, transport particles

However, they do transport electrons and react with 02. Other electron transport particles have been prepared by sonic oscillation. Under the electron microscope such particles appear to be small membranous vesicles resembling mitochondrial cristae. 

Electronic spectra provide a simple and convenient way to monitor changes induced in the oxidase by various chemical treatments. Indeed, spectral observations were at the core of the pioneering observations of MacMunn (12), Keilin (96), and Warburg (97) and more recently many investigators have examined the spectra of isolated oxidase, mitochondrial particles, and electron transport particles. The spectra of the fully oxidized [oxidase (IV)] (97a) and the fully reduced [oxidase (0)] oxidase have been well characterized (52) (Table V). In Table VI are spectral parameters for ligand complexes of various oxidation states (98-103). Although the spectra of most of these complexes have been... 

Fluorescent analogs of DCC are N-cyclohexyl-N -[4-(dimethylamino)-Q -naphthyl]carbodiimide (NCD ) and N-cyclohexyl-N -(l-pyrenyl)carbodiimide (PCD) which form fluorescent conjugates with mitochondrial electron transport particles or purified ATPase vehicles.N-cyclohexyl-N -(4-dimethylamino)-a-naphthylcarbodiimide... 

A more precise method of calibration, especially for complex solutions, is described in reference 14. This method involves complete oxidation of a known amount of NADH (spectrophotometrically determined) by an oxygen generating enzyme system such as heart mitochondria electron transport particles or diaphorase. 

Cobley JG (1976) Energy-conserving reactions in phosphorylating electron-transport particles from Nitrobacter winogradskyi. Activation of nitrite oxidation by electrical component of the proton motive force. Biochem J 156 481-491... 

Hgure 1 EPR spectra of electron transport particles (ETPs) from heart mitochondria from titration with NADH. (A) ETPs treated as other samples except that no reduclant was added (BHE) reduced with increased dose of NADH. (Reproduced with permission from Orme-Johnson N et al. (1974) Electron paramagnetic resonance-detectable electron acceptors in beef heart mitochondria. Journal of Biological Chemistry 249 1922-1939.)... 

There are many similarities between the photoelectron transport particle from photosynthesis, the quantasome, and the basic electron transport particle involved in oxidative phosphorylation in nonphotosynthetic cells. The latter particle, found in mitochondria and sometimes called the elementary particle or oxosome, is also probably a high molecular weight particle with dimensions in the order of 100 to 200 A. It contains a complement of cytochromes, non-heme iron proteins, quinones, etc., and performs the transport of electrons coupled to the formation of ATP. Thus, one can make a strong case for the evolutionary relationship between the basic oxidative electron transport particle and the photoelectron transport particle. Speculations as to which one came first in evolution are dependent upon what one assumes to have been the environmental conditions under which the evolution occurred. 

The advances in understanding of the structure of the photosynthetic apparatus are particularly encouraging, and we may look forward confidently to a detailed relation of biochemical function to morphological entities in the near future. The recent pictures of quantasomes (Park and Biggins, 1964) seem to reveal substructure. Will these subunits turn out to be Pigment Systems 1 and 2, intermediate electron transport particles, etc. ... 

ETP acronym of Electron transport particle (see). See also Mitochondria. 

Disruption of M. produces smaller fragments known as submitochondrial particles (SMP). SMP consist chiefly of fragments of inner membrane, which become resealed to form vesicles these are sometimes referred to as inside-out-particles , because the outer surface (i.e. exposed to the surrounding medium) corresponds to the inner surface of the membrane in the intact M. (i.e. exposed to the matrix). The method of disruption of M. (sonication, mechanical shear, detergents) and the intensity of its application determine the nature of the resulting SMP. The capacity for oxidative phosphorylation may be lost, but the particles may still actively respire (electron transport particles, ETP). On the oAer hand, careful and mild disruption of M. produces SMP that are still able to carry out oxidative phosphorylation. 

Quantosome the smallest structural unit of photosynthesis small elementary units of the thylakoid measuring 18 x 15 x 10 nm, M, 2 million, containing 230 chlorophyll molecules, cytochromes, copper and iron. Q. are obtained by ultrasonic disinte ation of isolated chloroplasts, and they can be visualized in the electron microscope. They can also be observed as granular units in the chloroplast lamella. The functional status of Q. is not clearly defined they may be involved in both electron transport and photophos-phorylation, and therefore analogous to the electron transport particles of the respiratory chain. 

From the previous section it is evident that our knowledge about the respiratory chain is still quite incomplete. We know which prosthetic groups participate (cf. diagram in Section 4). It remains to be clarified, however, to what proteins they are bound and what role the metals and any new cofactors might play. The reason for this unsatisfactory state of knowledge is that the enzymes under consideration are bound very firmly to the mitochondrial structure (cf. Chapt. XIX-3). Only very recently have techniques been developed to subdivide the mitochondria in such a manner that most of their activity is retained. The subunits thus obtained have been called electron-transport particles (Green and co-workers). Some of the catalytic capabilities have been sacrificed (e.g. the enzymes of the citric acid cycle). But they are still able to oxidize NADHs or succinate with consumption of Oj and formation of ATP (see below). With the further destruction of these subunits, the capacity for oxidative phosphorylation disappears. 

On this basis the respiratory chain of the electron-transporting particles may be written as follows ... 

The experiments were repeated, using electron transport particles instead of whole mitochondria, because in this preparation the mito -chondrial membrane is disrupted, which should make the cytochrome b more accessible. Also in this case, no reduction of the cytochrome b by the tetrahydropterin was observed. 

---