Complex III of the mitochondrial electron transfer chain is an asymmetric unit with a diameter of 80-100 Al and a molecular weight of about 300,000.2 Preparations of the complex contain 20-30 per cent by weight of lipid and (in the presence of bile salts) are water soluble.3 Under appropriate conditions (involving dilution of the bile salts), the units aggregate into vesicular membranes.4 The complex exhibits reduced coenzyme Q-cytochrome c reductase activity with high specific activity.3 The following accumulated evidence strongly supports the contention that the complex represents the subunit of the inner mitochondrial membrane which catalyzes the corresponding span (reduced coenzyme Q-cytochrome c reductase) of the electron transfer chain: (i) The complex has been prepared from mitochondria by three different procedures. All preparations have the identical composition in terms of their content of cytochromes and nonheme-iron protein.3 5 6 (ii) At all stages in the purification of the complex, the ratios cytochrome b: cytochrome cl (ref. 7) and nonheme-iron protein: cytochrome c1 (ref. 8) remain constant.1' 6 (iii) All preparations of the complex exhibit, on ultracentrifugal analysis, a single peak with constant sedimentation characteristics,2 consistent with the minimum particle weight as assessed by cytochrome cl content. (iv) The dimensions of the particle as seen by electron microscopy are consistent with this molecular weight, and are similar to the dimensions of the "base-piece" repeating units of the mitochondrial inner membrane. (v) The complex represents the purest form in which the component species have been isolated without loss of native characteristics relating to spectra, oxidation-reduction potential, and solubility. (vt) Specific inhibitors of reduced coenzyme Q-cytochrome c reductase (such as antimycin A) exhibit much the same inhibitory behavior with the isolated complex as with intact mitochondria.3 Cleavage of the complex results in loss of both enzymic activity and the capacity to bind antimycin A.9-1' By all the above criteria the complex must be considered as a single, integrated enzymic unit. Indeed it probably represents one of the best-documented examples of such a multiprotein enzyme. This is not to say that it might not be possible to demonstrate partial reactions both with the intact complex and with isolated fragments. All available evidence, however, suggests that such reactions would be, to some extent, artifactual. An intensive study has recently been made to extend the available knowledge of the composition and structural organization of the complex.1 10-12 In addition, certain significant observations relating to spectral changes in the active complex have also been reported.13 It is the purpose of this communication to integrate

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Mixtures of several sulfur amino acid oxidation products were formed in the oxidation of cystine, lanthionine, or homocystine by aqueous hydrogen peroxide in the presence of hydrochloric acid. After 10 min at 100 "C in 6% HzOz and 0.8 N HC1, cysteic acid was the main oxidation product of cystine; lanthionine sulfoxide, lanthionine sulfone, and unidentified products were also formed. In a similar oxidation of lanthionine, lanthionine sulfoxide was the most abundant product; cysteic acid, lanthionine sulfone, and unidentified products were also formed. An identical oxidation of homocystine afforded homolanthionine sulfoxide as the main product; homolanthionine sulfone and homocysteic acid were also formed. When homocystine was oxidized at 50 "C, homolanthionine was the principal product. However, when the HC1 concentration was increased to 4.8 N, homocysteic acid and homolanthionine sulfone were the main products. Sulfoxide produds were distinguished by reduction with dimethyl sulfide in the presence of HC1. Thus, they were converted into their corresponding sulfides and shifted to new chromatographic locations. These desulfurizations by hydrogen peroxide in the presence of HC1 are discussed in relation to known chemical changes of amino acids, including lanthionine formation, which occur in alkali-treated foods and to the use of peroxide in food technology.

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