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Ferredoxin isolated from a blue-green alga, Nostoc sp., was purified and crystallized. The absorption spectrum of Nostoc ferredoxin had, in the oxidized state, peaks at 276, 331, 423, and 470 nm, a pattern characteristic of chloroplast-type ferredoxin. The 423:276 absorption ratio was 0.57. The midpoint oxidation-reduction potential of Nostoc ferredoxin was found to be –406 mV, at pH 7.5. Nostoc ferredoxin mediated the photoreduction of NADP by isolated Nostoc chromato-phores and spinach chloroplasts from which the native ferredoxin was removed. The molar ratio of Nostoc ferredoxin to chlorophyll a was about 1:50, a ratio higher than usually found in photosynthetic cells. The possible evolutionary significance of the properties of Nostoc ferredoxin compared with those of ferredoxins from other photosynthetic organisms is discussed.

Purine nucleoside phosphorylase (purine nucleoside:orthophosphate ribosyltransferase, EC 2.4.2.1) has been purified 125-fold from the homogenate of chicken livers and some of the properties of the purified enzyme have been studied. This enzyme had a pH optimum at around 6.o. At high substrate levels of inosine the reaction rate was increased, suggesting that substrate activation of the enzyme had occurred. The enzyme activity was completely lost after 48 h at −20°. The inhibition by nucleotides and SO 4 2− is a characteristic of this enzyme and has not been previously reported.

1. 1.|5′-Nucleotidase (5′-ribonucleotide phosphophydrolase, EC 3.1.3.5) was partially purified from chicken liver. This is the first time it has been possible to obtain 5′-nucleotidase from the hepatic tissue of uricotelic animals and it was found to be kinetically distinct from 5′-nucleotidases obtained from other sources. 2. 2.|5′-Mononucleotides having a keto group at position 6 in the purine base are the most active substrates of this enzyme. 5′-IMP is the most active substrate among the 5′-nucleotides tested, and it is about 10 times more active than 5′-AMP. 3. 3.|This enzyme has an optimum pH at 6.5 and requires divalent metal ions. In the absence of divalent metal ions, the enzyme is almost inactive. 4. 4.|Inosino, guanosine p-chloromercuribenzoate (PCMB) and NaF inhibit this enzyme. Of these inhibitors, PCMB was found to be the most potent. 5. 5.|The general properties of the enzyme are described, and its possible metabolic function is discussed.

A crystallization procedure for Euglena and Chlamydomonas ferredoxin is described. With minor modifications this method is applicable to all microalgae. The absorption spectrum of crystalline Euglena ferredoxin showed maxima at 276, 328, 422 and 465 nm, and a shoulder at approx. 285 nm. The ratios of absorbances at 328, 422 and 465 nm to that at 276 nm were very high, namely 0.87, 0.68, and 0.60, respectively. The molecular weight estimated from chemical and sedimentation analyses is 11 000 ± 1 000. The protein contained 2 g atoms of iron and acidlabile sulfide per mole. Euglena ferredoxin differed from higher plant ferredoxins in having more aspartic acid than glutamic acid. We failed to obtain ferredoxin from dark-grown cultures of Euglena.

Publisher Summary Several cytochromes can be isolated from Euglena species, for example, c 552 , c -type 556, b -type 561 (558 and 563), and a -type 605. Only cytochrome c 552 has been highly purified and fully characterized. In the course of purification procedure of cytochrome c 552 , wild-type strains of Euglena gracilis are grown in an illuminated vessel at room temperature (25 ° ), and harvested after maximum growth is achieved. The cells are washed once with 0.9% NaCl and after centrifugation, the cell paste is stored at –15 ° C until used. Mutant strains may contain reduced amounts of cytochrome c 522 when grown under these conditions. Dark-grown Euglena strains do not contain this cytochrome. There are several methods for the extraction of the cytochrome c 552 , for example, with sulfuric acid, with digitonin, freezing and thawing, sonication, and acetone treatment. The acetone treatment gives the highest yield of cytochrome c 552 . This method also provides a high yield of ferredoxin. The freezing and thawing method is also recommended for the extraction process, although the recovery is lower and the ferredoxin is decomposed.