Is supercomplex organization of the respiratory chain required for optimal electron transfer activity?

The supra-molecular assembly of the main respiratory chain enzymatic complexes in the form of "super-complexes" has been proved by structural and functional experimental evidence. This evidence strongly contrasts the previously accepted Random Diffusion Model stating that the complexes are functionally connected by lateral diffusion of small redox molecules (i.e. Coenzyme Q and cytochrome c). This review critically examines the available evidence and provides an analysis of the functional consequences of the intermolecular association of the respiratory complexes pointing out the role of Coenzyme Q and of cytochrome c as channeled or as freely diffusing intermediates in the electron transfer activity of their partner enzymes.

Purification and properties of a new ribosome-inactivating protein with RNA N-glycosidase activity suitable for immunotoxin preparation from the seeds of Momordica cochinchinensis.

A ribosome-inactivating protein similar to those already known (Stirpe and Barbieri (1986) FEBS Lett. 195, 1-8) was purified from the seeds of Momordica cochinchinensis. This protein, for which the name of momorcochin-S is proposed, is a glycoprotein, has an Mr of approx. 30,000, and an alkaline isoelectric point and can be considered as an iso-form of the previously purified momorcochin from the roots of M. cochinchinensis. Momorcochin-S inhibits protein synthesis by a rabbit-reticulocyte lysate and phenylalanine polymerization by isolated ribosomes, and alters rRNA in a similar manner as the A-chain of ricin and related toxins (Endo et al. (1987) J. Biol. Chem. 262, 5908-5912). Momorcochin-S was linked to a monoclonal antibody (8A) against human plasma cells, and the resulting immunotoxin was selectively toxic to target cells.

Purification and properties of new ribosome-inactivating proteins with RNA N-glycosidase activity.

Ribosome-inactivating proteins (RIPs) similar to those already known (Stirpe & Barbieri (1986) FEBS Lett. 195, 1-8) were purified from the seeds of Asparagus officinalis (two proteins, asparin 1 and 2), of Citrullus colocynthis (two proteins, colocin 1 and 2), of Lychnis chalcedonica (lychnin) and of Manihot palmata (mapalmin), from the roots of Phytolacca americana (pokeweed antiviral protein from roots, PAP-R) and from the leaves of Bryonia dioica (bryodin-L). The two latter proteins can be considered as isoforms, respectively, of previously purified PAP, from the leaves of P. americana, and of bryodin-R, from the roots of B. dioica. All proteins have an Mr at approx, 30,000, and an alkaline isoelectric point. Bryodin-L, colocins, lychnin and mapalmin are glycoproteins. All RIPs inhibit protein synthesis by a rabbit reticulocyte lysate and phenylalanine polymerization by isolated ribosomes and alter rRNA in a similar manner as the A-chain of ricin and related toxins (Endo et al. (1987) J. Biol. Chem. 262, 5908-5912).

Purification and partial characterization of a mitogenic lectin from the latex of Euphorbia marginata.

A lectin was purified from the latex of Euphorbia marginata by affinity chromatography on acid-treated Sepharose 6B and elution with lactose. The lectin is a glycoprotein composed of two identical subunits with M(r) 30,000, approx. The haemagglutinating activity of the lectin is not specific for any human blood group, and is inhibited by galactose and galactose-containing sugars and by gentiobiose. The lectin is strongly mitogenic for human T-lymphocytes and induces the release of interleukin-1 beta and tumor necrosis factor-alpha from cultured mononuclear cells.

Purification and partial characterization of a lectin from the seeds of Trichosanthes kirilowii Maximowicz.

A lectin was purified from the seeds of Trichosanthes kirilowii, belonging to the family Cucurbitaceae, growing in China. The lectin is a glycoprotein of 57 kDa, consists of two subunits with apparent molecular masses of 37 and 25 kDa, is specific for galactose, and is not mitogenic for human lymphocytes.

Purification, characterization and biological activity of tulipin, a novel inhibitor of DNA synthesis of plant origin.

A DNA synthesis-inhibiting protein (for which the term tulipin is proposed) was isolated from the bulbs of Tulipa sp. The yield ranged from 3.4 to 4.1 per cent of total protein content of the crude extract. Mr, isoelectric point, neutral and amino sugar and amino acid composition were determined. Inhibition of DNA synthesis varied in intact cells according to the cellular types studied, with a minimum ID 50% (concentration giving 50% inhibition) of 400 ng/ml in neuroblastoma cells. The effect was reversible. No effect was obtained in cell-lysate. RNA and protein synthesis were unaffected. The acute toxicity, evaluated in Swiss mice, gave an LD of 6.1 mg/kg body wt. Results of electron microscopy are also given. A second protein, called tulipin 2, has been isolated and partially characterized.

Bryodin, a ribosome-inactivating protein from the roots of Bryonia dioica L. (white bryony).

Bryodin is a strongly basic (pI greater than or equal to 9.5) glycoprotein (neutral sugar content 6.3%) with Mr 30,000, purified from the roots of Bryonia dioica (white bryony). This protein inhibits protein synthesis by a rabbit reticulocyte lysate with and ID50 (concentration causing 50% inhibition) of 0.12 nM (3.6 ng/ml) and has much less effect on protein synthesis by whole cells, with ID50 values ranging from 46 nM to 2.27 microM (1.4-67 micrograms/ml). Bryodin acts by inactivating ribosomes, with a less-than-equimolar ratio, which suggests a catalytic action. Bryodin decreases the number of local lesions induced by tobacco mosaic virus in the leaves of Nicotiana glutinosa. From all its properties, bryodin can be considered to be a ribosome-inactivating protein, similar to those already known [reviews: Barbieri & Stirpe (1982) Cancer Surveys 1, 489-520; Stirpe & Barbieri (1986) FEBS Lett. 195, 1-8].

Properties of volkensin, a toxic lectin from Adenia volkensii.

Volkensin, a highly toxic protein from the roots of Adenia volkensii (kilyambiti, kinoria), was purified by affinity chromatography on acid-treated Sepharose 6B. The toxin is a glycoprotein (Mr 62,000, neutral sugar content 5.74%) consisting of an A subunit (Mr 29,000) and of a B subunit (Mr 36,000) linked by disulfide and noncovalent bond(s). The amino acid, amino sugar, and neutral sugar composition of the protein were determined. Volkensin is a galactose-specific lectin and is a potent inhibitor of eukaryotic protein synthesis in whole cells as well as in a cell-free system (a rabbit reticulocyte lysate). The inhibitory and the lectin activities are functions of the A and B subunits, respectively. Volkensin can be included amongst the ricin-like toxins and resembles most closely modeccin, the toxin of Adenia digitata.

Trichokirin, a ribosome-inactivating protein from the seeds of Trichosanthes kirilowii Maximowicz. Purification, partial characterization and use for preparation of immunotoxins.

A protein, here named trichokirin, was extracted from the seeds of Trichosanthes kirilowii and purified by ion-exchange and gel-filtration chromatography. Trichokirin is a basic glycoprotein of apparent relative molecular mass of 27,000 with a strong ribosome-inactivating activity. Alignment of the trichokirin, trichosanthin and momordin N-terminal sequences shows a substantial degree of homology. Trichokirin was conjugated to a monoclonal antibody directed against the Thy 1.2 antigen with the cleavable dimethyl 3,3'-dithiobispropionimidate cross-linking reagent. This immunotoxin selectively killed leukemia cells expressing the Thy 1.2 antigen. The addition of ammonium chloride, which increases the cytotoxicity of ricin A-chain immunotoxins, blocks that of the trichokirin immunotoxin, suggesting that they enter cells by different mechanisms. In vivo studies showed that the pharmacokinetic properties of the trichokirin immunotoxin could be more advantageous than those of the ricin A-chain immunotoxins for in vivo applications.

Ribosome-inactivating proteins (RNA N-glycosidases) from the seeds of Saponaria ocymoides and Vaccaria pyramidata.

From the seeds of the Caryophyllaceae Saponaria ocymoides and Vaccaria pyramidata two proteins were purified which have the properties of the type-1 (single-chain) ribosome-inactivating proteins [reviewed by Barbieri, L., Battelli, M. G. & Stirpe, F. (1993) Ribosome-inactivating proteins from plants, Biochim. Biophys. Acta 1154, 237-282]. The proteins have molecular masses of 30.2 kDa (S. ocymoides) and 28.0 kDa (V. pyramidata) and pI greater than 9.5, their N-terminal amino acid sequences are similar to those of saporin-S6 and dianthin 30, ribosome-inactivating proteins from other Caryophyllaceae, and they partially cross-react with sera against these proteins. Both proteins inhibit protein synthesis by a rabbit-reticulocyte lysate with IC50 (concentrations giving 50% inhibition) below 10(-10) M, have a smaller effect on poly(U)-directed phenylalanine polymerisation by rat liver ribosomes (nanomolar IC50, approximately) and on protein synthesis by various cell lines (IC50 ranging from 4 nM to > 3000 nM) and possess rRNA N-glycosidase activity, releasing 1 mol adenine/ribosome.

Ribosome-inactivating proteins from plant cells in culture.

1. Ribosome-inactivating proteins were found in high amounts in one line of cells of Phytolacca americana (pokeweed) cultured in vitro and, in less quantity, in lines of Saponaria officinalis (soapwort) and of Zea mays (corn) cells. 2. The main ribosome-inactivating protein from pokeweed cells was purified to homogeneity. It is a protein with Mr 29,000 and basic pI, similar to the 'pokeweed antiviral protein' (PAP), a ribosome-inactivating protein from pokeweed leaves. We propose to call the pokeweed antiviral protein isolated from pokeweed cells PAP-C. 3. PAP-C inactivates ribosomes in a less-than-equimolar ratio, thus inhibiting protein synthesis by a rabbit reticulocyte lysate with an IC50 (concentration causing 50% inhibition) of 0.067 nM (2 ng/ml), and modifies rRNA in a manner apparently identical to that of ricin and other ribosome-inactivating proteins. It inhibits protein synthesis by intact cells with an IC50 of 0.7-3.4 microM, and is toxic to mice with an LD50 of 0.95 mg/kg.