1. Micrococcus denitrificans excretes three catechol-containing compounds, which can bind iron, when grown aerobically and anaerobically in media deficient in iron, and anaerobically in medium with a high concentration of Ca2+. 2. One of these compounds was identified as 2,3-dihydroxybenzoic acid (compound I), and the other two were tentatively identified as N1N8-bis-(2,3-dihydroxybenzoyl)spermidine (compound II) and 2-hydroxybenzoyl-N-L-threonyl-N4[N1N8-bis-(2,3-dihydroxybenzoyl)]spermidine (compound III). 3. The equimolar ferric complex of compound III was prepared; compound III also forms complexes with Al3+, Cr3+ and Co2+ ions. 4. Cell-free extracts from iron-deficient organisms catalyse the formation of compound II from 2,3-dihydroxybenzoic acid and spermidine, and of compound III from compound II, L-threonine and 2-hydroxybenzoic acid; both reactions require ATP and dithiothreitol, and Mg2+ stimulates activity. The enzyme system catalysing the formation of compound II has optimum activity at pH 8.8 Fe2+ (35muM), Fe3+ (35muM) and Al3+ (65muM) inhibit the reaction by 50 percent. The enzyme system forming compound III has optimum activity at pH 8.6. Fe2+ (110 muM), Fe3+ (110 muM) and Al3+ (135 muM) inhibit the reaction by 50 percent. 5. At least two proteins are required for the formation of compound II, and another two proteins for its conversion into compound III. 6. The changes in the activities of these two systems were followed after cultures became deficient in iron. 7. Ferrous 1,10-phenanthroline is formed when a cell-free extract from iron-deficient cells is incubated with the ferric complex of compound III, succinate, NADH and 1,10-phenanthroline under N2.

A rapid, single-step purification of the alkaline phosphatase of Escherichia coli using salt gradient chromatograpy on DEAE-cellulose is described. The product is homogeneous by electrophoretic and ultracentrifugal criteria and its amino acid composition is documented. The specific activity of the resultant enzyme is equivalent to that of the crystalline material (Malamy, M. H., and Horecker, B. L. (1964), Biochemistry 3, 1889).

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Gibson, Neuberger & Tait (1962b) have shown that ethionine inhibits the biosynthesis of bacteriochlorophyll and stimulates the excretion of coproporphyrin by illuminated suspensions of Rhodopseudomonas spheroides, and that this effect can be reversed by methionine. It was suggested that methionine might be concerned in a specific manner in the formation of bacteriochlorophyll, and evidence was presented to show that the methyl group of methionine is a direct precursor of the methyl ester group of bacteriochlorophyll. Tait & Gibson (1961) reported that chromatophores from Rps. spheroides catalyse the transfer of the methyl group of S-adenosylmethionine to magnesium protoporphyrin to form a compound that was tentatively identified as magnesium protoporphyrin monomethyl ester. The present paper describes the further characterization of the enzyme, S-adenosylmethionine-magnesium protoporphyrin methyltransferase, and the identification of the product formed.

Gibson, Neuberger & Tait (1962) mentioned briefly that, when ethionine was added to suspensions of Rhodop8eudomona8 8pheroides illuminated in 'mixture I' of Lascelles (1956), large amounts of porphyrin accumulated in the medium, although growth and bacteriochlorophyll synthesis were inhibited. This was rather surprising since other inhibitors of growth prevented the formation of porphyrin and bacteriochlorophyll. In the present paper the effect of ethionine is described in more detail. Of a large number of other compounds only threonine was found to have a similar effect. In the presence of ethionine or threonine the synthesis of bacteriochlorophyll can be restored and porphyrin excretion reduced by methionine or homocysteine. These results suggested that ethionine exerts its effect by interfering with the synthesis or utilization of methionine. This was confirmed when it was found that the methyl ester group of bacteriochlorophyll is formed from the methyl group of methionine. Some of these results have been briefly presented earlier (Neuberger, 1961; Gibson, Matthew, Neuberger & Tait, 1961).