A study of the kinetics of aconitase inhibition and activation

The relationship between iron and the activity of aconitase purified from the leaves of mustard (Sinapis alba)

“…The effect of 2,2'-bipyridyl was slow, causing 100 % inhibition after 5 days. Herr et al (1956) obtained about 50 % inhibition with ophenanthroline (1 mM) after 20 min. preincubation with the enzyme.…”

“…He therefore concluded that 1 molecule each of Fe2+ ion and reducing agent react with the active centre to form an enzyme-Fe2+-activator complex. Herr et al (1956), however, showed that the addition of Fe2+ ions and cysteine to freshly prepared aconitase, and to a preparation that had lost nearly all activity after dialysis, brought about a similar increase in activity. The loss in activity caused by dialysis was not recovered by the addition of Fe2+ ions and cysteine, and these workers conclude that iron functions in the utilization of chemical groups on the enzyme which may be different from those utilized in the absence of iron.…”

“…Aconitase, however, is considered to be specific for Fe2+ ions (Dickman & Cloutier, 1951;Morrison, 1954 b). Chelating agents depress the activity of aconitase only after preincubation with the enzyme (Dickman & Cloutier, 1951;Herr et al 1956). This type of effect would be expected if the metal was firmly bound to the enzyme, but is difficult to explain if the metal is dissociable.…”

“…The Relationship between Iron and the Activity of Aconitase Purified from the Leaves of Mustard (Sinapis alba) BY M. J. PALMER* Department of Biochemi8try, Macaulay In8titute for SOil Re8earch, Aberdeen (Received 16 December 1963) The activity of aconitase from iron-deficient tissues of both animals (Beutler, 1959) and plants (Bacon, DeKock & Palmer, 1961b) has been found to be lower than that from normal tissues. Such studies had been prompted by reports that the enzyme purified from animal tissues is dependent on Fe2+ ions and cysteine for maximum activity (Dickman & Cloutier, 1951;Morrison, 1954b;Herr, Sumner & Yesair, 1956). There is no report of the purification of aconitase from plant sources.…”

Effect of E DTA on Chlorophyll Synthesis and Root Elongation of Anthoxanthum odoratimi

“…KARATAGLIS (1977) reported that the absence of EDTA from a nutrient solution resulted in an increase in the uptake of metal ions. Other investigators have found that EDTA stimulates the activity of certain enzymes by removal of traces of inhibitory heavy metals (ALTMANN and CROOK 1953, HERR et al 1956, WEIN STEIN et al 1956, MARSH et al 1963, MARTHUR et al 1973). The unusual chelating properties of EDTA lead one to suspect that EDTA in the proper concentration will inhibit the activity of heavy metal-activated enzymes where the metal-enzyme combination is loosely bound.…”