All known living cells contain NAD+ (Nicotinamide Adenine Dinucleotide) and NADP+ (Nicotinamide Adenine Dinucleotide Phosphate), as these are essential coenzymes for life as we know it.

Both NAD+ and NADP+ act like shuttles for molecules, they pick up and drop off electrons and hydrogen protons.

NAD+ structure contains a pyridine ring C₅H₅N (nicotinamide ring) and it is a reactive part meaning it can accept electrons and H+. The ring is where electron accepting and donating happens.

When NAD+ accepts H+/electrons, it becomes NADH.

The pyridine ring is like a hook that can grab and release electrons and H+.

NADH, on the other hand, plays a role in ATP generator during human cellular respiration, delivering electrons to the electron transport chain in the human mitochondria. Each NADH can help generate 2.5 ATP (simplified).

Relationship with UV light

NADH absorbs UV light at around 340nm. When NADH absorbs UV, it becomes fluorescent. Excited at 340nm it emits at around 460nm. NAD+ does not have this property.

Interestingly, you could measure NADH/NAD+ using UV light as a consequence.

Human Decline

NAD+ decline with age. Energy production in mitochondria becomes less efficient.

When this happens, pseudo-hypoxic state is achieved = cells behave as if they are lacking oxygen even though O2 is abound.

On top of that, communication between cell nucleus and mitochondria breaks down and they cannot coordinate properly — “mitonuclear discordance”.

Oxygen

Oxygen is the final acceptor in the ETC. It accepts electrons at Complex IV and converts to water H2O with no deuterium.

Oxygen “pulls” electrons through the chain.

The electron pull is essential to maintain the flow, keeping ETC efficient, preventing electron backup and essentially maintaing normal ATP production.

UV/ECT

Exposure to UVB light increases the expression of CYP P450 1A1 and CYP 1B1 mRNA in epidermal cells.

UV might affect NADH→NAD+ conversion therefore affecting electron availability on the ETC.

UV light can affect NADH redox state and influence electron availability at Complex 1, therefore affecting the whole ETC flow.

UV and ROS

ROS are important for cellular signalling, they need tight control and the excess is harmful.

UV light increases free radicals in the cell — all oxygen-based free radicals are ROS, not all ROS are free radicals.

Some argue that just enough UV light and proper oxygenation are required to balance stable free radicals in mitochondria to signal optimally.

Linked

https://pubs.acs.org/doi/10.1021/acssensors.4c00118#

https://www.molbiolcell.org/doi/10.1091/mbc.e15-06-0390

https://onlinelibrary.wiley.com/doi/abs/10.1111/php.13661

Definitions

  • NAD+ = Nicotinamide Adenine Dinucleotide (oxidized form)
  • NADH = Nicotinamide Adenine Dinucleotide (reduced form)
  • NADP+ = Nicotinamide Adenine Dinucleotide Phosphate (oxidized form)
  • ATP = Adenosine Triphosphate
  • UV = Ultraviolet
  • UVB = Ultraviolet B (wavelength range 280-315 nm)
  • ETC = Electron Transport Chain
  • ROS = Reactive Oxygen Species
  • CYP = Cytochrome P450 (enzyme family)
  • mRNA = Messenger Ribonucleic Acid
  • O2 = Molecular Oxygen
  • H2O = Water
  • H+ = Hydrogen Ion/Proton