Where do all the NAD+s come from?

Question

In the mitochondrial respiration (of plant cells) NADH is reduced from Nad+ as part of the TCA (converting malate to oxaleoacetate). But where do the NAD+s come from? The TCA cycle is working even in isolated mitochondrias by adding malate as a substrate, which indicates NAD+ must be present already. I am also wondering if ADP and NAD+ can be transfered through the inner membranes of the mitochondrion without specific channels?

Answer 1

NAD+ is made in cells from amino acids (aspartic acid and tryptophan) or via the Preiss-Handler pathway from nicotinic acid. There is also a salvage pathway that allows for the recycling of nicotinamide.

Both ADP and NAD+ would require a transporter; however, there is much debate about which form enters the mitochondria (cytosolic nicotinamide (NAM), nicotinamide mononucleotide (NMN), or NAD).

Answer 2

Great question! NAD is made in two ways.. either directly from amino acids coming together ( de novo synthesis) or by the break down of other molecules (salvage pathway) like niacin/B vitamins. That's why these vitamins and amino acids are so important for us in our diet!

In regards to how it gets in mitochondria, I do not believe it can enter through simple diffusion. I believe it needs to be transported but I do not know the name of the protein. This is the same for ATP and ADP, they do not simply diffuse into the mitochondria either and need a "shuttle".