Question

What are the published values are for Km, pH optimum, activation energy, and the mode of inhibition are for vanadate?

Answer 1

PH: 6.7

At pH 6.7 (the pH optimum of the ATPase), inhibition is half-maximal between 0.45 and 1.0 PM vanadate, depending upon the ionic composition of the reaction medium.

Km is the concentration of substrates when the reaction reaches half of Vmax. A small Km indicates high affinity since it means the reaction can reach half of Vmax in a small number of substrate concentration. This small Km will approach Vmax more quickly than high Km value.

All chemical reactions, including exothermic reactions, need activation energy to get started. Activation energy is needed so reactants can move together, overcome forces of repulsion, and start breaking bonds.

a vanadate is a compound containing an oxoanion of vanadium generally in its highest oxidation state of +5. The simplest vanadate ion is the tetrahedral, orthovanadate, VO3−
4 anion, which is present in e.g. sodium orthovanadate and in solutions of V2O5 in strong base (pH > 13[1]). Conventionally this ion is represented with a single double bond, however this is a resonance form as the ion is a regular tetrahedron with four equivalent oxygen atoms.

Vanadate is a potent inhibitor of certain plasma membrane ATPases, such as Na+/K+-ATPase and Ca2+-ATPase (PMCA). Acting as a transition-state analog of phosphate, vanadate undergoes nucleophillic attack by water during phosphoryl transfer, essentially "trapping" P-type ATPases in their phosphorylated E2 state. it does not inhibit other ATPases, such as SERCA (sarco/endoplasmic reticulum Ca2+-ATPase), actomyosin ATPase and mitochondrial ATPase