STUDIES ON ALGAL CYTOCHROME II PHYSICO-CHEMICAL PROPERTIES OF CRYSTALLINE PORPHYRA TENERA CYTOCHROME 553

The Physico-chemical properties of an algal cytochrome, Porphyratenera cytochrome 553 were investigated, using a crystallinepreparation of the substance. The cytochrome was found to behighly resistant to heat and preservation. The stability ofthe cytochrome was also prominent in a wide range of pH. Absorption spectra as: well as data concerning the extinctioncoefficients of the oxidized and reduced forms are presented. The oxidation-reduction potential of the cytochrome was determinedat various pH. The value for the normal potential was foundto decrease gradually with increasing pH; from 355 mV at pH5.0, to 270 mV at pH 11.0. Electrophoretic investigation revealedthat this cytochrome is a markedly acidic protein, with an isoelectricpoint of pH 3.5. The molecular weight of the cytochrome wasdetermined from ultracentrifugal and diffusion experiments tobe 13,600. The values for the minimum molecular weight calculatedfrom the heme- and iron-contents are, respectively, 12,000 and11,000. (Received April 20, 1960; )