Enzymatic inhibition

The work that paved the way toward enzymatic inhibition was published in the early 1990s by Wudl and coworkers (Schinazietal., 1993 Friedmanetal., 1993 Sijbesma et al., 1993) and since then studies regarding antiviral activity, mainly HIV-protease inhibition, have been carried out to find active compounds. Up to now, the most effective fullerene derivatives are the trans-2, -dimethy 1-bis-fulleropyrrolidin-ium salt (Fig. 1.4) (Marchesan et al., 2005) and the dendrofullerene reported by Hirsch (Schuster et al., 2000) both of them present an ECJ0 of 0.2pM. Also HIV reverse transcriptase can be inhibited by, -dimcthyl-bis-fulleropyrrolidinium salts (Mashino et al., 2005). The same compounds are also active against acetylcholine esterase (AChE), an enzyme that hydrolyzes a very important neurotransmitter. 

The most recent advances on enzymatic inhibition are related to endonucleases and polymerases. A tris-malonic acid fullerene derivative can interfere with DNA restrictive enzymatic reactions, demonstrating a dose-dependent inhibition of these enzymes, with an IC50 in the micromolar range. The addition of ROS scavenger does not revert the enzymatic activity, indicating that the fullerene action should be exerted in a direct way (Yang et al., 2007d). 

Ungell AL, Andreasson A, Lundin K, Utter L (1992) Effects of enzymatic inhibition and increased paracellular shunting on transport of vasopressin analogues in the rat. J Pharm Sci 81 640-645. 

The clinical pharmacology of saw palmetto in humans is not well defined. One week of treatment in healthy volunteers failed to influence 5oo-reductase activity, DHT concentration, or testosterone concentration. Six months of treatment in patients with BPH also failed to affect prostate-specific antigen (PSA) levels, a marker that is typically reduced by enzymatic inhibition of 5ct-reductase. In contrast, other researchers have reported a reduction in epidermal growth factor, DHT levels, and antagonist activity at the nuclear estrogen receptor in the prostate after 3 months of treatment with saw palmetto in patients with BPH. 

Avoiding Substrate Inhibition, Enzymatic Inhibition, and Catabolite Repression When using the fed-batch operation, the concentration of a substrate can be kept at a low value so that substrate inhibition, enzymatic inhibition, or catabolite repression is practically avoided, which results in high productivity [14]. 

Extrapolating from well-characterized enzymatic inhibition in test tubes, numerous mechanistic ideas concerning the in vivo effects of vanadium compounds have been advanced. The effects of vanadium compounds as transition-state analogs of certain enzymes with a phosphoprotein intermediate in their reaction scheme is proposed to account for the action of vanadium [11] in many biological systems. Unfortunately, it is often difficult to determine if the inhibition observed in the test tube occurs in vivo. For example, although vanadate is a potent inhibitor of plasma membrane ion pumps (such as the sodium potassium ATPase) in the test tube, it is difficult to determine if these pumps are actually inhibited in animals exposed to vanadium compounds. Currently, the role of vanadium compounds as protein phosphatase (PTP) inhibitors is believed to be related to the metabolic effects of this... 

In other recent reports concerning enzymatic inhibition and receptor binding of organofullerene materials, C60 monomalonate adducts were found to selectively inactivate the neuronal nitric oxide synthase isoform in a manner completely preventable by the concurrent presence of superoxide dismutase and catalase [295]. Also two fullerene-steroid hybrids were synthesized and found to decrease both the ATP hydrolysis and Ca2+ uptake activity of SR Ca2+-ATPase while the inhibitions were concentration dependent [296]. 

The toxic effects produced by ammonium are (i) enzymatic inhibition (in glycolysis, TCA cycle, glutaminolysis, and PPC) (ii) perturbation of the transcellular ionic gradient (iii) intracellular pH modification (iv) increase of UDP-GNAc synthesis, with concomitant glycolysis modification and affecting the quality of the recombinant protein and (v) increase in the alanine secretion. 

Conrad LS, Damhus T, Kirk O et al (1997) Enzymatic inhibition of dye transfer. Inform 8 950-957... 

H S Gill, D Eisenberg (2001) The Crystal Structure of Phosphinothricin in the Active Site of Glutamine Synthetase Illuminates the Mechanism of Enzymatic Inhibition, Biochemistry 40(7) 1903-1912... 

Information regarding the substrate activity of Reel was central to the development of substrate-based inhibitors. Investigation with farnesylated cysteine and farnesylated tetrapeptides did, however, result in enzymatic inhibition. The carboxylate terminus of a prenylcysteine modified with an aldehyde was found to be a low micromolar inhibitor [21]. Rando and coworkers also investigated modified farnesylated tetrapeptides. By modifying the substrate to remove the scissile bond, the potent statine-tetrapeptide (Figure 9.1) was discovered and has low nanomolar activity against Reel in crude membrane fractions. 

Peptidic monohalomethyl ketones inactivate serine proteinases by irreversibly reacting with the active-site histidine [101]. However, because of the reactivity pattern and the mechanism of action shown by these compounds, they are described in this section. Although initially prepared as inhibitors of other proteinases, monohalomethyl ketones contributed to the studies on elastase-ligand interactions. They supplied key data points on (a) the effect of the peptide substrate length on the binding, and (b) the subsite specificity of PPE and HLE. Kinetic evaluation of these compounds indicated a two-step mechanism for enzymatic inhibition (Equation 2.2). 

ASTM. 1994. Proposed test method for fluorometric determination of toxicity-induced enzymatic inhibition in Daphnia magna. ASTM 1994 Annual Book of Standards Vol. 11.04, E-47 Proposal P 235. American Society for Testing and Materials, West Conshohocken, PA, pp. 1717-1721. 

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