Porphyrin and corrinoid mutants of Bacillus subtilis.

Porphyrin auxotrophs of Bacillus subtilis can be divided into two groups. Strains belonging to the first group (hemA, hemB, or hemC) are not able to synthesize or metabolize porphobilinogen. These strains require cysteine, cystine, and methionine, respectively. Traces of aminolevulinic acid, in a hemin-containing medium, can replace the cysteine requirement in a mutant lacking aminolevulinic acid synthetase. In bacteria belonging to the second group (hemE, hemF, or hemG), porphyrin biosynthesis is blocked at later steps, and the amino acids mentioned above are not required. It is of interest that both the activity of ribonucleotide reductase and the amount of vitamin B12 were significantly lower in the first group. The addition of vitamin B12 to the medium did not promote the growth of strains examined. We assume that porphobilinogen deaminase is essential for the synthesis of corrinoids.     

Porphyrin in Vogelfedern

Ohne Zusammenfassung     

Porphyrin formation byArthrobacter globiformis

The extraction properties, absorption spectra, and chromatographic behaviour of the red extracellular pigment in cultures ofArthrobacter globiformis grown in a mineral salts-glucose medium were identical with those of coprophyrin III. Iron and zinc in small amounts were required for maximum production of the porphyrin. Large amounts of iron failed to suppress porphyrin accumulation in spite of their complete removal from the medium by the bacteria. The effect of iron on porphyrin metabolism in microorganisms is discussed. Accumulation of the porphyrin was highest with moderate aeration; it was almost completely suppressed upon exposure of porphyrin-accumulating cultures to low as well as high aeration rates. At a low aeration rate it was restored by addition of succinic acid, glutamic acid or δ-aminolevulinic acid but at a high aeration by δ-aminolevulinic acid only. At a low aeration rate more porphyrin was formed from δ-aminolevulinic acid than at a high rate.     

Porphyrin cytochrome c. pH effects and interaction with cytochrome-c oxidase

1. Porphyrin cytochrome c, the iron-free derivative of cytochrome c, has been used extensively as a fluorescent analog of cytochrome c. It appears as though its fluorescence intensity but not its relative quantum yield is affected by pH in the physiological range; an apparent pK of about 6.2 is found suggesting a histidine close to the porphyrin. 2. The fluorescence intensity of the porphyrin cytochrome c in the presence of cytochrome c oxidase is independent of pH; this suggests that the oxidase has the capacity to control the pK of whichever group is responsible for the pH sensitivity of the free porphyrin cytochrome c. The most likely candidate for this pH-sensitive group is histidine-18. The N-3 nitrogen of this residue forms one of the axial ligands to the iron in the intact cytochrome c but it is uncoordinated in the iron-free derivative.     

Porphyrin biosynthesis. Immobilized enzymes IV. Studies on aminolaevulate dehydratase attached to Sepharose

Summary Bovine liver aminolaevulate dehydratase (ALAD) has been chemically attached to Sepharose 4B and its properties have been studied. The optimal conditions for coupling have been determined. It was found that the immobilized enzyme retained a significant percentage of the activity of the free enzyme. The coupling yield was rather high. The insolubilized enzyme requires both anaerobiosis and a thiol activator for maximal activity. It can be stored at 4 °C for long periods with little loss of activity and it can be repeatedly used without alteration of its enzymic capacity. Attachment of ALA-D to the gel has led to an enhanced thermal stability. pH optima of free and bound enzyme was the same while a small decrease in the Km of the matrix bonded ALA-D as compared to that of the soluble enzyme was observed. The use of the fixed-ALA-D for the preparation of PBG is described.Dedicated to Professor Luis F. Leloir on occasion of his 70th Birthday.