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The half-reactions involved in the lactate dehydrogenase (LDH) reaction and their standard reduction potentials are

Pyruvate +2H鈦+2e鈦烩啋Lactate

狈础顿鈦+2贬鈦+2别鈦烩啋狈础顿贬+贬鈦

Calculate 鈭咷 at pH 7.0 for the LDH-catalyzed reduction of pyruvate under the following conditions:

  1. [lactate]/[pyruvate]=1 and [NAD鈦篯/[NADH]=1
  2. [lactate]/[pyruvate]=160 and [NAD鈦篯/[NADH]=160
  3. [lactate]/[pyruvate]=1000 and [NAD鈦篯/[NADH]=1000
  4. Discuss the effect of the concentration ratios in Parts a-c on the direction of the reaction.

Short Answer

Expert verified

In solution (a), the free energy change value at pH 7.0 for the LDH-catalyzed reduction of pyruvate under the given condition is -25.1kJ mol鈦宦.

In solution (b), the free energy change value at pH 7.0 for the LDH-catalyzed reduction of pyruvate under the given condition is 0.

In solution (c), the free energy change value at pH 7.0 for the LDH-catalyzed reduction of pyruvate under the given condition is 9.1 kJ mol鈦宦.

In solution (d), the reaction continues spontaneously in the backward direction.

Step by step solution

01

Pyruvate

Pyruvate is the result of glycolysis, and it has two possible outcomes. It passes via aerobic respiration in the aerobic process and fermentation in the anaerobic process. Pyruvate fermentation can take two forms: lactic acid fermentation and alcoholic fermentation.

02

In the solution (a), [lactate]/ [pyruvate]=1 and [NAD鈦篯/[NADH]=1

The two reactions are given as,

笔测谤耻惫补迟别+2贬鈦+2别鈦烩啋尝补肠迟补迟别

狈础顿鈦+2贬鈦+2别鈦烩啋狈础顿贬+贬鈦

The coupled reaction is,

笔测谤耻惫补迟别+2贬鈦+2别鈦烩啋尝补肠迟补迟别+NAD鈦

The free energy change equation is,

螖蔚=螖蔚'-RTnFlnlactateNAD+pyruvateNADH

On substituting,

螖蔚=0.130V-RTnFln1=0.130V螖骋=-296485JV-1mol-10.130V=-25.1kJmol-1

03

In the solution (b), [lactate]/ [pyruvate]=160 and [NAD鈦篯/[NADH]=160

The free energy change equation is,

螖蔚=螖蔚'-RTnFlnlactateNAD+pyruvateNADH

On substituting,

螖蔚=0.130V-RTnFln160160=0V螖骋=0

04

In the solution (c), [lactate]/[pyruvate]=1000 and [NAD鈦篯/[NADH]=1000

The free energy change equation is,

螖蔚=螖蔚'-RTnFlnlactateNAD+pyruvateNADH

On substituting,

螖蔚=0.130V-RTnFln10001000=-0.047V螖骋=-296485JV-1mol-1-0.047V=9.1kJmol-1

05

In solution (d), Effect of concentration ratios

The 鈭咷 is negative in part a, so the reaction is still moving ahead. Because the 鈭咷 value is zero, the part b area represents the equation in the equilibrium state. Parts c has a good positive value for 鈭咷. As a result, the reaction proceeds in a retrograde direction of its own accord.

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