Studies on the porphobilinogen deaminase–uroporphyrinogen cosynthetase system of cultured soya-bean cells

Abstract

1. Porphobilinogenase was isolated and purified from soya-bean callus tissue; its components, porphobilinogen deaminase and uroporphyrinogen isomerase, were separated and purified. 2. The purified porphobilinogenase was resolved into two bands on starch-gel electrophoresis. The molecular weights of porphobilinogenase, deaminase and isomerase fractions were determined by the gel-filtration method. Porphobilinogenase activity was affected by the presence of air; uroporphyrinogens were only formed under anaerobic conditions, although substrate consumption was the same in the absence of oxygen as in its presence. 3. pH-dependence of both porphobilinogenase and deaminase was the same and a sharp optimum at pH 7.2 was obtained. Isomerase was heat-labile, but the presence of ammonium ions or porphobilinogen afforded some protection against inactivation. The action of several compounds added to the system was studied. Cysteine, thioglycollate, ammonium ions and hydroxylamine inhibited porphobilinogenase; certain concentrations of sodium and magnesium salts enhanced activity; some dicarboxylic acids and 2-methoxy-5-nitrotropone inhibited the deaminase. 4. delta-Aminolaevulate and ethionine in the culture media stimulated porphyrin synthesis and increased porphobilinogenase activity, whereas iron deficiency resulted in porphyrin accumulation. 5. The development of chlorophyll and porphobilinogenase on illumination of dark-grown callus was followed. 6. A hypothetical scheme is suggested for the enzymic synthesis of uroporphyrinogens from porphobilinogen.

Protochlorophyll and Chlorophyll Biosynthesis in Cell-Free Systems from Higher Plants

“…The uroporphyrinogen formed during the lag phase accounted for only part of the porphobilinogen consumed. The authors concluded that a pre cursor of uroporphyrinogen must have accumulated during the lag phase (95,96). They looked for such an intermediate in the incubation mixture and detected a uv absorbing species similar in its absorption properties to monopyrroles.…”

“…It is compat ible, however, with the presence of two substrate binding sites on the porpho bilinogenase. Ammonium ions appear to act competitively at the first binding site (96). From (13) and Cornford's (20) hypotheses.…”

Control of Free Methionine Production in Wild Type and Ethionine-resistant Mutants of Chlorella sorokiniana

“…Ethionine is known to inhibit Chl synthesis in cultured soybean cells (13), presumably by antagonizing the methylation of Mg protoporphyrin by S-adenosylmethionine. However, in other organisms ethionine is known to act in one or more of several different ways (1), and resistant mutants are known to use various counteracting mechanisms, of which overproduction of methionine is but one (11).…”

The porphyrias: a review.

“…The precise source of succinyl coenzyme A used for ALA synthesis is unknown and there may well be a separate pool of this compound not directly formed via the Kreb's cycle. Secondly, the mechanism of formation of uroporphyrinogens I and III from porphobilinogen remains obscure although numerous theories have been proposed (Llambias and Batlle, 1970). There is need for this to be established as there are almost certainly enzymic deficiencies of this pathway other than that of uroporphyrinogen III co-synthetase in congenital erythropoietic porphyria.…”