1. The hemD gene, encoding uroporphyrinogen III synthase, has been located adjacent to the hemC gene at 85 min on the Escherichia coli chromosome. 2. The entire nucleotide sequence (741 base pairs) of the hemD gene is reported. 3. E. coli strains harbouring plasmics containing the hemD gene produce greatly elevated levels of uroporphyrinogen III synthase. 4. Purified uroporphyrinogen III synthase, isolated from the hemD-containing strain ST1046, has an Mr of 29,000, in close agreement with that predicted from the nucleotide sequence. 5. The existence of a hem operon is suggested.

The Escherichia coli hemD gene, encoding the enzyme uroporphyrinogen III synthase (co-synthase), was cloned into multi-copy plasmids in E. coli cells that were used to generate strains producing up to 1000 times the concentration of the synthase in the wild-type. The enzyme was purified to homogeneity from these strains in milligram amounts. The enzyme is a monomer of Mr 28,000 with an isoelectric point of 5.2 and a pH optimum of 7.8. The specific activity of the purified synthase is 1500 units/mg and the Km for the substrate, pre-uroporphyrinogen, is 5 microM. The N-terminal sequence of the enzyme is Ser-Ile-Leu-Val-Thr-Arg-Pro-Ser-Pro-Ala-Gly-, in agreement with the gene-derived protein sequence. The enzyme contains four 5,5'-dithiobis-(2-nitrobenzoic acid)-titratable groups, one reacting rapidly with the reagent and three further groups having lower reactivity. The enzyme is heat-sensitive, and during heat inactivation all four thiol groups become equally available for reaction.

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Aim: The aim of the study was to carry out a comparative analysis of the phytochemical composition of the leaves of four selected tropical medicinal plants namely: Ocimum gratissimum, Piper guineense, Gongronema latifolium and Vernonia amygdalina. Methodology: The phytochemicals in the plant leaves were extracted by cold maceration in ethanol and subjected to both qualitative and quantitative analysis of the phytochemicals. Results: The qualitative and quantitative analysis revealed the presence of the bioactive compounds alkaloids, Saponins, flavonoids, steroids, glycosides, terpenoids, polyphenols, specific cardiac glycosides, tannins, phytates and reducing compound in the leaves of each plant at varying quantities. Resins were only detected in O. gratissimum. From the quantitative analysis, Gongronema latifolium had the highest percentage content of alkaloids, glycosides, saponins, tannins and reducing sugars. Ocimum gratissimum had the highest flavonoid content. Conclusion: Taken together, G. latifolium on balance had a higher phytochemical content than the other three plants and thus should be more versatile in the treatment of a whole range of diseases. This was followed by V. amygdalina, O. gratissimum and P. guineense in that order. The fact that most of these phytochemicals have antioxidant activity may be responsible for their antidiabetic activities and use in treatment of other free radical prone diseases.