“…Nitrite reductase from P. aeruginosa (Horio et al, 1961), which was initially studied as cytochrome oxidase but was referred to later as nitrite reductase (Yamanaka & Okunuki, 1974), and those from M. denitriJicans (Lam & Nicholas, 1969;Newton, 1969) and Alcaligenes faecalis (Iwasaki & Matsubara, 1971) also contained haem c and d. In the present investigations haem c and d were shown to be in the ratio of 1 : 1 as was also reported for nitrite reductase from P. aeruginosa (Horio et al, 1961) and A. faecalis (Iwasaki & Matsubara, 1971). The molecular weight of the T. denitrijicans nitrite reductase was 120000, in agreement with the enzyme from M. denitriJicans (Newton, 1969) and P. aeruginosa (Gudat, Singh & Wharton, 1973). Values of 90000 and 85000 have also been reported for the P. aeruginosa enzyme (Horio et al, 1961;Newton, 1969).…”