BioPHYSICAL chemistry

CHAPTER 6 REDOX REACTIONS AND BIOENERGETICS 119

CH 2

HH

H

OH OH

H

O

O O

C

NH 2

O PR

H

O

N



CH 2

HH

H

OH OH

In NADP this hydroxyl group

is esterified with phosphate

H

O

O O

O P O

C

NH 2

2e

2H

O

HH HH

N

N

NH 2

N N

N

:

R

C

NH 2  H

O

N

:

Figure 6.3The oxidation of NAD+to NADH is a two-electron process with the release of only one proton.

1.0

0.5

0.0

Fraction reduced

Midpoint potential, Em

Potential (mV)

Absorbance

Wavelength, λ (nm)

Fully

reduced

Partly

reduced

Fraction

reduced

Fully

oxidized

Isobastic

point

Platinum

electrode

Reference

electrode

Light Absorbance

log

Titration
cuvette

Syringe

containing

chemical

titrant to

adjust

potential

Voltmeter

Measured

potential

Figure 6.4The determination of midpoint potentials using redox titrations.