The haem prosthetic group of lactoperoxidase can be prepared from the enzyme in high yield by reductive cleavage with mercaptoethanol in 8 M-urea under mild conditions. The product yields porphyrins, after removal of iron, which show visible spectroscopic properties similar to protoporphyrin but are considerably more polar. In the presence of iodoacetamide, a different product is obtained by reductive cleavage. The proton n.m.r. and mass spectra of this compound indicate that the prosthetic group of the enzyme is the iron complex of 18-mercaptomethyl-2,7,12-trimethyl-3,8-divinylporphyrin-13,17-d ipropionic acid. It is proposed that the unusual strength of binding of the prosthetic group to the apoprotein is due to formation of a disulphide bond from a cysteine residue to the porphyrin thiol.
A mixture of triethyl orthoformate and
trifluoroacetic acid has been developed as a means of formulating certain pyrroles and dipyrrylmethanes. The advantages and
disadvantages of the procedure are discussed. The use of p-toluenesulphonic acid with orthoformate converts pyrroles
into tripyrrylmethanes.
A number of symmetrical
dipyrrylthiones have been prepared by the action of thiophosgene on the
appropriate 5-unsubstituted pyrrole. From an examination of their spectroscopic
properties it is concluded that these compounds exist predominantly as the
thione tautomer. Some chemical properties of the system are described including
the conversion of the thiones into ketones by treatment with alkaline peroxide.
The mass spectra of dipyrrylthiones and dipyrrylketones are compared.
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