Enzyme Inhibitors

Hydroxyurea is a compound used in anti-cancer research to inhibit DNA synthesis and in sickle cell research for ways to alleviate symptoms. It has been shown to be a potent inhibitor of ribonucleotide reductase which reduces ribonucleotides to deoxyribonucleotides.

In vivo research has shown hydroxyurea converting into a free radical nitric oxide which binds the active site of ribonucleotide reductase, ceasing further DNA synthesis. The mechanism of nitric oxide release from hydroxyurea is not well understood.

Hydroxyurea has also been shown to alleviate sickle cell anemia through its conversion to nitric oxide in vivo. Nitric oxide alleviates endogenous nitric oxide loss, caused by hemolysis, and stimulates soluble guanylate cyclase (sGC) activity which will signal fetal hemoglobin production.

Imazapyr is imidazolinone family herbicide that has been used to research herbicidal resistances and biochemical pathways in an array of plants. This compound has been shown to uncompetitively inhibit acetolactate synthase (ALS) which catalyzes the production of the amino acids valine, leucine and isoleucine. Loss of these specific amino acids depletes physiologically important proteins and enzymes, eventually resulting in cell death.

Leupeptin hemisulfate (Ac-Leu-Leu-argininal) is a reversible inhibitor of serine and cysteine endopeptidases. Leupeptin hemisulfate is capable of inhibiting plasmin, trypsin, papain, kallikrein, calpain and cathepsin B. Leupeptin is usually used in a concentration range of 10 to 100μM. Leupeptin is widely used in many protease inhibitor cocktails due to its potency, low toxicity, and range of inhibition. Leupeptin is also used in a quantitative assay to measure macroautophagic flux in mammals and is being investigated for its use in treating malaria.

Pepstatin A is a competitive, reversible aspartic protease inhibitor and inhibits proteases such as pepsin, chyomsin, renin, HIV proteases, and cathepsins D and E. Peptstatin A is highly selective and is often used in a mixture with other enzyme inhibitors. In vitro studies have shown pepstatin A is the only aspartic acid inhibitor that exhibits inhibitory effects on HIV proteases.

Pepstatin A is effective at inhibiting most affected proteases at a concentration of 1μM, but can inhibit pepsin at the picomolar range of concentrations. It is believed to function by way of a collected-substrate inhibition mechanism. Pepstatin A may also suppress differentiation of osteoclasts by inhibiting phosphorylation of MAP kinase and inhibiting NFATc1 expression.

Sodium orthovanadate is a general competitive inhibitor of tyrosine specific phosphatases, acid and alkaline phosphatases and ATPases. Phosphatase inhibition from Vanadate may be completely reversed by dilution or by the addition of EDTA.

Trypsin inhibitor is a serine protease inhibitor from soybeans that is specific for trypsin and trypsin-like proteases. Trypsin inhibitor from soybeans is a monomeric protein containing 181 amino acid residues in a single polypeptide chain cross-linked by two disulfide bridges. Soybean trypsin inhibitor forms a 1:1 complex with the active protease site. Inhibition may be reversed and is pH dependent. The optimal pH for trypsin binding is 8.0.