STUDIES ON MICROSOMAL CYTOCHROMES 

 AND RELATED SUBSTANCES 



By C. F. Strittmatter 



Department of Biologieal Chemistry, Harvard Medical School, 

 Boston, Massachusetts 



In this paper I shall attempt to review the development of our knowledge 

 concerning the microsomal cytochrome of mammahan liver and related 

 compounds, as this story provides a case history of the problems in identi- 

 fication, characterization, nomenclature and elucidation of biological 

 significance of cytochromes which is one of the major concerns of this 

 Symposium. 



IDENTIFICATION, LOCALIZATION AND CHARACTERIZATION 



The ''Liver-type^ Cytochrome Spectrum 



The pioneer spectroscopic studies of MacMunn (1884, 1886) established 

 that haemochrome-like compounds are widely distributed in tissues of 

 vertebrate and invertebrate animals, and that the haemochrome complement 

 of different animal cells differs both with type of tissue and with the species. 

 In examinations of what he termed the 'histohaematin' spectra of tissues, 

 MacMunn noted that heart and skeletal muscle from a variety of species 

 showed, particularly in the presence of a reducing agent, a characteristic 

 absorption spectrum which he labelled 'myohaematin'. This myohaematin 

 spectrum was the four-banded spectrum of what is now commonly regarded 

 as the typical 'muscle-type' cytochrome system, first intensively studied by 

 Keilin (1925) with the strong a-bands of cytochromes a (and a-^ at about 

 605 m//, of cytochrome b at about 562-566 m/i and of cytochrome c (and c^) 

 at about 550-553 m^ respectively, and the fused weaker /5-bands of cyto- 

 chromes at 520-530 vl\[x. MacMunn noted that the 'histohaematin' spectra 

 of many other tissues were similar to that of muscle, but that spectra of some 

 tissues, most notably liver and the analogous green gland of certain in- 

 vertebrate groups, and the adrenal medulla, were distinctly different. Char- 

 acteristically, these 'liver-type' spectra showed a feeble band in the 605 m/^ 

 region, and the bands of cytochromes b and c appeared to be replaced by a 

 single broad band, generally with no distinct absorption maximum, which 

 apprbximately spanned the region normally bounded by the oc-bands of 

 cytochromes b and c. 



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