Enzymes, inhibition, substrate specificity

Recombinant human ER mannosidase I has been expressed and purified and the enzyme has many catalytic characteristics in common with the yeast enzyme, including substrate specificity, the requirement for Ca+ for catalytic activity, and inhibition by DMJ and KIF, but not Sw [105], A recombinant epitope-tagged form of the human enzyme is also localized to the ER of mammalian cells indicating a conservation of localization as well as function of this ER enzyme [105],... 

MAO is known to occur in at least two forms, MAO A and MAO B, based on substrate selectivity, inhibition by various dmgs, and cloning experiments. Clorgyline [17780-72-2] is a specific inhibitor of MAO A, which displays a substrate specificity for NE and serotonin. Deprenyl [2323-36-6] is a selective inhibitor of MAO B, and displays a substrate preference for P-phenylethylamine and benzyl amine. Dopamine and tyramine are substrates for both enzymes. 

Tyrosine is converted to dopa by the cytoplasmic enzyme tyrosine hydroxylase. This is the rate-limiting step 5 x 10 M) in DA synthesis, it requires molecular O2 and Fe + as well as tetrahydropterine (BH-4) cofactor and is substrate-specific. It can be inhibited by a-methyl-p-tyrosine, which depletes the brain of both DA and NA and it is particularly important for the maintenance of DA synthesis. Since the levels of tyrosine are above the for tyrosine hydroxylase the enzyme is normally saturated and so it is not possible to increase DA levels by giving tyrosine. 

The desulfinase enzyme was reported to have narrow substrate specificity. In addition to HBPSi, only 2-phenyl benzene sulfinate was reported to serve as a substrate [164], It was found to be inactive against benzene sulfinate, cysteine sulfinate, benzene sulfonate, /7-toluene sulfonate, 1-octane sulfonate, methane sulfonate, and taurine. This enzyme was found to be inhibited by HBP beginning at 0.5 mM with complete loss of activity at 9 mM HBP, but was not affected by sulfite. 

---