Pyruvate complex

We have modelled the [CDopen - methyl pyruvate] complex. The result is shown in Figure 2. In this complex there is no steric hindrance to prevent the free rotation of the substrate around the quinuclidine nitrogen. Thus, in complex shown in Figure 2. there is no preferential stabilization of the substrate. In earlier computer modeling it was suggested that Pt is involved in the stabilization of the [CDopew-a-lfeto ester] complex, i.e. the Pt surface prevent the free rotation of the substrate, however the driving force for enantio-differentiation, i.e. for preferential adsorption of the substrate, was not discussed [14]. 

Monte-Carlo simulation method was used to investigate the interaction of the [CDdosed-MePy] complexes with Pt (111) surface. The result shown in Figure 5 indicates that the shielded complex can maintain its entity even after adsorption. Further computer modeling indicated that there are other molecules with the ability to induce SE. In this respect Troger s bases are of particular interest. The calculated Troger s base-methyl pyruvate complex (R form) is shown in Figure 6. 

Figure 3. The shielded form of [CD-methyl pyruvate] complex, (R ) form...

Figure 2 The open fonn of cinchonidine-methyl pyruvate complex.

Figure 5. The adsorption of CD - methyl pyruvate complex over Pt(l 11) surface.

Figure 6, Troger s base-methyl pyruvate complex.

The conformational analysis of methyl pyruvate shows that it can have two conformers. In the second conformer the two carbonyls are in syn position. The anti-syn conformational change requires 3 kcal. The [CDqIq qJ - methyl pyruvate ] complex ((R) form) was also calculated and shown in Figure 8. In the above complex the "directionality" of the lone pair of electrons of the quinuclidine nitrogen is advantageous for interactions with both the keto and the ester carbonyl groups. 

The chelated phosphoramidate (22) is formed as an intermediate in the reaction of [Co(NH3)5(DNPP)]+ in alkaline solution, through intramolecular nucleophihc attack of a deprotonated m-ammine (Scheme 1). Similar reactivity is observed in the monodentate pyruvate complex [Co(NH3)50C(0)C(0)CH3] +, where the imino carboxylate chelate (23) is formed at pH > 12. ... 

The chicken liver enzyme pyruvate carboxylase also has a natural requirement for Mn. The distances between Mn and the carboxyl and carbonyl carbon atoms of pyruvate (8) in the enzyme-pyruvate complex... 

The kinetics of LMO has been extensively studied. In a reversal of what is observed in most flavoenzymes, the oxidized flavin in LMO is nonfluorescent, while the reduced flavin is fluorescent giving a useful signal for stopped-flow studies. The flavin is reduced by lactate at 230s at pH 7.0 and 25 °C. The reduced enzyme-pyruvate complex formed exhibits long-wavelength charge-transfer absorbance and is nonfluorescent. Finally, at a rate too slow to be catalytically relevant, the fluorescence of free reduced enzyme appears as pyruvate dissociates. Thus, oxygen reacts with the reduced enzyme—pyruvate complex. ... 

The catalytic mechanisms of LOX and LMO are very similar, with one key exception. The rate of pyruvate dissociation is much faster in LOX than in LMO. LOX catalyzes a true ping-pong mechanism, which can be divided into two distinct half-reactions. In the reductive half-reaction, LOX is reduced as lactate is oxidized to pyruvate. ° Flavin reduction occurs at 105 s at 4°C at 25 °C, the reaction is too fast to be measured. A fourfold primary isotope effect is observed on this step when using a- H-lactate as a substrate. The product of lactate oxidation is the reduced enzyme/pyruvate complex, which exhibits long-wavelength charge-transfer absorbance. Product dissociation from this complex occurs at 35 s about 7000-fold faster than pyruvate dissociation in LMO. In the oxidative half-reaction, the free reduced enzyme, formed due to the quick release of pyruvate, is oxidized by molecular oxygen with a second-order rate constant of... 

Various reasons for the advantages gained in the specialization of major LDH isozymes have been proposed (68,69,71-74) One possibility may be in the greater degree of pyruvate inhibition of the H4 isozyme (1,36,69) as a result of the formation of the abortive ternary LDH NAD-pyruvate complex (see Section III,C,3). 

Fio. 22. Relative movements of C atoms between the apoenzyme and the LDH NAD-pyruvate complex. The distance for each residue is plotted along the radius of a polar graph where the angle is proportional to sequence number, (a) Change in radial component of Co atoms from substrate. Atoms which move toward the substrate in the ternary complex are plotted negatively. (b) Magnitude of complete movement between equivalent C atoms. 

Molecular investigation of the inhibition was initiated by Fromm s (258) discovery that the enzyme forms a complex with NAD+ and pyruvate which has an absorption band at 325 nm and a protein fluorescence of 0.12 relative to the apoprotein. A similar compound can be formed if NAD+ is replaced by 3-acetylpyridine-AD which has an absorption band at 355 nm (259,260). Subsequent structural investigations have been summarized by Kaplan and co-workers (260,261). Two observations show that formation of the LDHzNAD-pyruvate complex is the cause of inhibition by high concentrations of pyruvate. First, the dissociation... 

The recent recognition that the LDH NAD-pyruvate complex is very... 

These data clearly show the enhancement in the stabilities of the "mixed species. For example at 25 the constant for the addition of pyruvate (or glycinate) to the glycinate (or pyruvate) complex is about 19-23 times greater than it is for the addition of the ligand to either the aquo Ni(ll) or Zn(II) ion. Mn(II) is somewhat unusual since the prior coordination of one of the components of the mixed complex produces a 32 fold increase in the constant for toie coordination of the other. 

NAD -pyruvate complex, which was first investigated in detail, was found to be a binary complex because it contains a covalent bond... 

It is of interest to note that the thiol form of TPP contains the j3-thiol-ethylamine configuration present in coenzyme A. The fact that glutathione, coenzyme A, and the pyruvate oxidation factor all are sulfur-containing compounds is highly suggestive of the possibility that TPP is also active in the thiol form. Cavallini has recently shown that in vitro at pH 7.4, the oxidation of GSH by oxygen in the presence of traces of copper or cytochrome c may be coupled with a simultaneous oxidation of pyruvate to acetate and CO2. The reaction probably depends on the intermediate formation of a GSH-pyruvate complex and is suggested as a possible model for the action of TPP. 

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