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Utilization of simple algorithmic schemes coupled with chemical data and the known conformational requirements of metal ions has resulted in the prediction of the basic tertiary structure of a metalloprotein, the hemerythrin subunit.
The standard redox potentials of soluble cytochromes c isolated from the green alga Chlorella and the blue-green algae Spirulina and Aphanezomenon were determined by potentiometric titration and found to be equal to +380 mB, +330 mB and +357 AB, respectively. The standard redox potentials of plastocyanin preparations from Pisum sativum and Atriplex leaves were also determined and found close to those of soluble cytochromes c, i. e. +395 mB and +375 mB, respectively. The metalloproteins studied were shown to belong to monoelectron carriers operating at the donor sites of photosystem I.
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The native dimeric form of methionyl-tRNA synthetase of Escherichia coli contains two zinc atoms per dimer, one per subunit. The bound zinc is retained upon trypsin modification which yields a monomer with one zinc atom. The enzymatic activity of both the dimeric forms is reversibly inhibited by 1,10-phenanthroline but not by its non-chelating analogues. In addition, the native enzyme binds two Mn2+ per dimer with a binding constant of approx. 70 micron but no binding is observed with the trypsin-modified monomer.
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Various free radicals formed on pulse radiolysis of aqueous solutions have been used to investigate the mechanisms of reduction of cytochrome(III) c by inter- and intramolecular electron transfer. The rapid formation of free radicals (t less than 1 mus) and their high reactivity with cytochrome (k approximately 10(8)(-5) x 10(10)M(-1)s(-1)) make such studies feasible. Reduction of cytochrome by free radicls is monitored by optical methods. Fast optical changes in the 1(-500)-mus region correspond to reduction of the iron center; whereas the slower changes in the 10(-500)-ms region are attributed to postreduction conformational changes. It has been concluded that the reduction path is mediated through the crevice and that no reduction intermediates are being formed.
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Orgotein is a copper- and zinc-containing protein with superoxide-dismutase activity which can be isolated from bovine liver and erythrocytes. The effects of this drug on adjuvant -induced arthritis in rats, and particularly on the changes in erythrocytes sedimentation rates and plasma fibrinogen levels induced by this experimental infection, were studied. Orgotein was also assayed on nystatin-induced paw edema, passive cutaneous anaphylaxis and Arthus reaction, in rats. Finally, studies on platelet aggregation and the prostaglandin system were conducted. Given at doses of 2.5 and 5 mg/kg i.p. for 14 days to arthritic rats, orgotein normalized the serum changes, inhibited the foot swelling and improved the performance time on the rotating bar. The drug reduced, after a single dose, the nystatin-induced edema, whilst it showed no effects on the immunological inflammations, platelet aggregation and prostaglandin system. The probable mechanism of action is discussed.
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The effects of various metall-containing proteins (plastocyanin, plantacyanin, azurine and cytochromes of the f type) on the activity of photosystem I of chloroplasts, treated with polyene antibiotics, were studied. The inhibiting effect of the polyenes, surgumycin and philipin, was completely removed by an addition of copper-containing protein plastocyanin. No similar effect was exerted by other Cu-containing proteins--azurine and plantacyanin. The cytochromes of the f type isolated from the green algae chlorella, blue-green algae spiruline and aphanezomenone, having different electrophoretic properties, restored the activity of photosystem I of chloroplasts incubated with antibiotics in a different degree. Acid cytochrome f of chlorella restored the activity by 80--100%; less acid cytochrome f from spiruline-only by 50%. The least restoring effect was exerted by aphanezomenone cytochrome, which possesses some basic properties. The chloroplasts treatment with surgumycin did not affect the isolation of the terminal enzyme of the chloroplast electron-transporting chain of ferredoxin--NADP--reductase. Possible environment of plastocyanin in the chloroplast membrane and the mechanism of photosystem I restoration are discussed.
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