Control of Porphyrin Biosynthesis through a Negative-Feedback Mechanism. STUDIES WITH PREPARATIONS OF δ-AMINOLAEVULATE SYNTHETASE AND δ-AMINOLAEVULATE DEHYDRATASE FROM RHODOPSEUDOMONAS SPHEROIDES

Publisher Website
Google Scholar
Abstract
The enzyme, [delta] -aminolaevulate synthetase, was purified about tenfold from extracts of R. spheroides. Significant inhibition of the synthetase was caused by 0.1 [mu]M-Fe protoporphyrin (hemin); the highest concentration tested (0-2 m[image]) inhibited the enzyme by about 87%. Other Fe por-phyrins inhibited to a similar extent, whereas protoporphyrin and other metal complexes of protoporphyrin were less effective. Hemoglobin and myoglobin were also inhibitory. The inhibition by hemin was not competitive with any of the substrates or cofactors, but was reversible by dilution. Porphyrin formation from glycine and [alpha]-oxoglutarate by whole-cell suspensions of R. spheroides was inhibited by hemin, but conversion of [delta] -aminolaevulate into porphyrins was unaffected. The characteristics of the inhibition of the synthetase, and the results with whole cells indicate that 1 mechanism for control of porphyrin biosynthesis in R. spheroides may be through negative feedback by hemin. Succinyl-coenzyme-A thiokinase and [delta]aminolaevulate dehydratase were purified by about 170- and 70-fold respectively from extracts of R. spheroides. [delta] -Aminolaevulate dehydratase was only slightly inhibited by hemin. It required K+ ions for activation.