466 C. F. Strittmatter 



DISTRIBUTION OF MICROSOMAL CYTOCHROME AND 

 SIMILAR HAEMOCHROMES 



There have been observations in many biological materials and derived 

 preparations of haemochrome-like materials variously described as identical 

 with or similar to microsomal cytochrome, cytochrome m or cytochrome b^,, 

 but in many cases the identity of the haemochrome-like materials and their 

 possible relationsliip to the well-characterized microsomal cytochrome are 

 uncertain by reason of insufficiently rigorous or specific tests of identity. 

 Many of these substances are defined solely or largely on the basis of the 

 absorption spectra of an unpurified preparation, particularly by the appear- 

 ance of an absorption band in the 555-560 m/t region under fairly strong 

 reducing conditions, or by the demonstration of protoporphyrin haemochrome 

 with such preparations. In many instances these observations appear to 

 represent non-specific absorption, since protohaem may be combined with 

 various non-specific or denatured proteins and with other possible nitro- 

 genous components or contaminants of tissue preparations to yield haemo- 

 chromes with reduced absorption spectra almost identical with that of 

 the microsomal cytochrome, and adsorbed haemoglobin or denatured 

 protein haemochromes are common contaminants of tissue preparations 

 unless care is exercised to exclude or remove them (cf. Slater, 1949; Stritt- 

 matter and Ball, 1952; Strittmatter, 1952; Klingenberg, 1958). Moreover, 

 as the early studies of 'Z>i-like' bands already indicated, an apparently homo- 

 geneous absorption band may result from a group of absorbing substances 

 (not necessarily including one absorbing maximally at the observed absorp- 

 tion maximum) and caution must be exercised even in interpretation of the 

 absorption spectrum of an optically clear extract or 'solution', particularly 

 one which shows uncharacteristic asymmetries (cf. Fujita and Kodama, 1934; 

 Slater, 1949; Strittmatter, 1952; Strittmatter and Ball, 1952, 1954; Hulsman, 

 Elliott and Rudney, 1958). On the other hand, of course, minor differences 

 of properties between different preparations or different purified substances 

 need not exclude the essential identity of the active substances concerned. 



Distribution in Mammalian Tissues 



Haemochrome materials with an absorption maximum in the region 

 555-560 m/t have now been reported in preparations from a number of 

 mammalian tissues in addition to fiver, including adrenal medulla (MacMunn, 

 1886; Huszak, 1942; Ryan and Engel, 1957; Spiro and Ball, 1958), mam- 

 mary gland (Bailie and Morton, 1955, 1958), intestinal mucosa (Bailie and 

 Morton, 1955), ovary (MacMunn, 1886; Yoshikawa, 1951), pancreas 

 (Palade and Siekevitz, 1956), and kidney (Yoshikawa, 1951), but the identity 

 of the absorbing materials in many cases is not clearly estabhshed. As to 

 intracellular distribution, studies on localization of well-defined microsomal 



