Substrate, competitive

Active site directed P-lactam-derived inhibitors have a competitive component of inhibition, but once in the active site they form an acyl en2yme species which follows one or more of the pathways outlined in Figure 1. Compounds that foUow Route C and form a transiendy inhibited en2yme species and are subsequendy hydroly2ed to products have been termed inhibitory substrates or competitive substrates. Inhibitors that give irreversibly inactivated P-lactamase (Route A) are called suicide inactivators or irreversible inhibitors. The term progressive inhibitor has also been used. An excellent review has appeared on inhibitor interactions with P-lactamases (28). 

It follows that for precursor feeding to be competitive, substrate costs would have to be reduced by 35.05 - 2830 = 635 kg 1. So, the percentage reduction in substrate... 

Two heterocyclic phosphonates have been designed and synthesized in an attempt to identify more spatially conHned, planar analogs of glyphosate than obtained previously with the pyridine analog 111 (75). Molecular modeling experiments suggest that 5-phosphono-thiazolin-2-one 133 and 5-phosphono-l,2,4-triazolin-3-one 137 each may overlap either with glyphosate or its known competitive substrate, phosphoenolpyruvate (PEP), very well (5). 

II. Active carrier-mediated Flux is saturable with increasing concentration. Competitive substrates. Flux may be asymmetrical. Flux can be against an electrochemical gradient. Energy dependent—directly or indirectly coupled. Substrate specificity, competition, saturation. Flux is asymmetrical. 

The three models used are described by Eq. (6-8) below. The Eqn. (6) is the first-order model based on Michaelis-Menten model, Eqn. (7) is the second-order model, and the Eqn. (8) is the competitive-substrate model. Rso represents the initial specific reaction rate for the substrate S. 

The answer is c. (Katzung, pp 827-828J Famciclovir is active against herpes simplex and varicella zoster viruses. It is activated by a viral kinase to a triphosphate. The triphosphate is a competitive substrate for DNA polymerase The incorporation of the famciclovir triphosphate into viral DNA results in chain termination. 

Lleo, A., Waldron, E., von Amin, C.A.F., et al. (2005) Low density lipoprotein receptor-related protein (LRP) interacts with presenilin 1 and is a competitive substrate of the amyloid precursor protein (APP) for y-secretase. J. Biol. Chem., 280, 27303-27309. 

Most of these substances are hydrolyzed more slowly than acetylcholine and so act as competitive substrates for Achase. Edorphonium is simply a competitive inhibitor since it cannot undergo hydrolysis. 

Synergism - a potentiation or prolongation which results in much greater than expected effects. This could involve competitive substrates for an enzyme or receptor, decreased excretion, displaced plasma protein binding, etc. The analgesic propoxyphene (Darvon ) slows down the excretion of ethanol and so increases the depressant effects of the alcohol. Recall the example given earlier of the monoamine oxidase inhibitors used as antidepressants and the tyramine-containing foods which could precipitate a hypertensive crisis. 

Fig. 2 Free enthalpy diagram for the complexation of the specific guest A to host W in relation to the competitive substrates B and 2B.

Iodothyronines acting as competitive substrates, where it has been demonstrated that a) inhibition is independent of whether the analogue undergoes the same or the alternative reaction (IRD or ORD) and b) the K value of the analogue is identical to its Km as a substrate [7,8]. 

That the type II deiodinase represents a common enzyme for the ORD of T4 and rT3 is supported by their mutual competitive inhibition with corresponding Km and /C( values [72-74,82,83]. T3, which is not a substrate for the type II deiodinase, also does not inhibit the deiodination of T4 and rT3 in vitro. In addition to competitive substrate inhibition, other mechanisms exist for the regulation of type II enzyme activity by thyroid hormone in vivo. Experimental hypothyroidism in rats induces a large increase in type II activity in the CNS [71,82], pituitary [72,83,87] and BAT [73] at least in part by prolongation of the half-life of the enzyme [88]. Treatment of hypothyroid rats with T3 produces a rapid fall in type II deiodinase in CNS and pituitary which appears to be due to an accelerated inactivation of the enzyme [88]. 

Dumont demonstrated [14] that the esterification of myristic acid by ethanol has shown to follow Ping Pong Bi Bi kinetics with competitive substrate inhibition by ethanol ... 

A -Methyltyramine (phenolic amine) Palicourea marcgravii (Rubiaceae) [leaf] MAO-A (competitive substrate) [may T toxicity of Fluoroacetate in same plant]... 

Such interference falls into two classes competitive substrates and substances that either aaivate or inhibit the enzyme. With some enzymes, such as urease, the only substrate that reacts at reasonable rate is urease hence, the urease-coated electrode is specific for use (59, 165). Likewise, uricase acts almost specifically on uric acid (167), and aspartase on aspartic acid (8, 168). Others, such as penicillinase and amino oxidase, are less specific (63,169,170). Alcohol oxidase responds to methanol, ethanol, and allyl alcohol (171, 172). Hence, in using electrodes of these enzymes, the analyte must be separated if two or more are present (172). Assaying L-amino acids by using either the decarboxylative or the deaminating enzymes, each of which acts specifically on a different amino... 

Troutman, J.M., Subramanian, T., Andres, D.A., and Spiehnann, H.P. (2007). Selective modification of CaaX peptides with ortho-substituted anihnogeranyl lipids by protein farnesyl transferase competitive substrates and potent inhibitors from a library of farne-syl diphosphate analogues. Biochemistry 46 11310-11321. 

Yermg, D.T., Lenz, D.E., Cerasoli, D.M. (2005). Analysis of active-site amino-acid residues of human serum paraoxonase using competitive substrates. FEBS J. Til 2225-30. 

In the reverse reaction, free ADP gives competitive substrate inhibition versus MgADP. MgATP and MgADP do not show substrate inhibition as they are too large to fit into the site for AMP or ADP. 

In competitive substrate binding experiments, the polymers showed selectivity for the templates with which they were made. On the other hand, non-templated control polymers showed statistical preference for both substrates. Some results on the substrate selectivities of these polymers are presented in Table 6.1. It is particularly notable from this study that these imprinted polymers could distinguish positional isomers (4 and 5), which differ in their imidazole spacing by only 4 A. 

Renal tubular dysfunction is described in animals but human expression in unclear [12]. Most use of mTOR inhibitors is in conjunction with lowered doses of calcineurin inhibitors since it is known that these two drug classes have a potent drug-drug interaction leading to enhanced renal dysfunction compared to the calcineurin inhibitor alone [782]. This may be explained by inhibition of drug efflux pump P-glycoprotein since both siroiimus and the calcineurin inhibitors are competitive substrates [783, 784]. 

A. Metabolic activation The antimetabolites (and their subsequent enzymic reaction product(s), respectively) may be utilized as competitive substrate(s) in one (or several consecutive) enzymic reaction(s) along the metabolic pathway of the normal metabolite, but at one stage of the metabolic reaction sequence, the transformed analogue cannot be further utilized as a substrate and, instead, acts as an inhibitor of the enzyme which catalyzes the next reaction step. At this stage, the action of the transformed ( activated ) analogue as an enzyme inhibitor depends on the same general types of structural requirements as outlined in the case of the directly acting enzyme inhibitors (see Section 2.2. ... 

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