**2.3 Magnesium the magic molecule in metabolic recession**

Magnesium serves as key ingredient in the recipe of lipid lunch as both the pivotal enzymes are activated in the presence of magnesium as a cofactor. There have been two schools of thoughts as far as role of magnesium on these enzymes are concerned the one thinks that magnesium is activating substrate by binding to it (magnesium-substrate complex) while other view rests on the idea that magnesium binds to the active site inducing conformational change and having catalytic role for efficient catalysis (2007).

The plant and bacterial ICL have an absolute requirement of Mg2+ ions for functional activity. Mg2+ ions were postulated to be necessary for catalysis on the active site of ICL however, a higher concentration of these ions has been found to have inhibitory effect on the enzyme (Beeckmans et al., 1997). Later on, Giachetti et al. (Giachetti & Vanni, 1991) performed detailed kinetic studies with *Pinus pinea* ICL and concluded that the Mg2+ isocitrate complex and not isocitrate is the true substrate of enzyme. This conclusion has been supported by studies on ICL from several other sources. In the absence of divalent cations, only negligible activity was measured for the purified ICL, whereas addition of Mg2+ or Mn2+ supported enzyme activity. Mn2+ was able to replace Mg2+, yielding 39% of the activity obtained with Mg2+. Co2+, Fe2+, Ca2+, Ba2+, Ni2+, Cd2+, Zn2+, Cu2+, and Hg2+ were not able to support significant ICL activity (Honer Zu Bentrup et al., 1999). A variety of metal ion combinations were studied for their ability to inhibit ICL activity. It is known for the isocitrate lyases of *Corynebacterium glutamicum* and *Acinetobacter calcoaceticus* that Mn2+ can partially substitute for Mg2+ (Hoyt et al., 1988; Hoyt et al., 1991).In the absence of divalent cations only negligible activity was measured for the purified MS. Mg2+ at 5 mM was found to be the most effective cation. Mn2+ was able to replace Mg2+, yielding 40% of the activity obtained with Mg2+, Co2+, Fe2+, Ca2+, Ba2+, Ni2+, Cd2+, Zn2+, Cu2+, and Hg2+ were not able to support significant MS activity (Smith et al., 2003). Zn2+ and Cd2+ were found to bring about structural alterations thereby inhibiting the function of enzyme in case of MtbIcl (Kumar & Bhakuni, 2008).
