I was wondering what would be the most stable physiological buffer for nicotinamide adenine dinucleotide (NAD+), for potential storage as frozen aliquots - 6 months stability or around there would be ideal. A buffer that is physiologically compatible is essential (e.g. suitable for in vivo use).
I would also be interested in potential solubility limits. I've seen reports of people achieving up to 200 mg/mL solutions, but others stating that they made 50 mg/mL.
I have read from Sigma that
NAD is soluble in water at 50 mg/mL, and that an aqueous solution may be made by adjusting the pH using NaOH or a sodium bicarbonate buffer.
Does this not imply that a carbonate buffer would be usable? They then also state that
As per external source information β-NAD is soluble in PBS pH 7.2 at 10mg/ml.
This to me implies that a phosphate buffer would be suitable. However, they finally said the following:
Aqueous solutions between pH 2 - 6, stored as single-use aliquots at -70 °C, are stable for at least 6 months. Neutral or slightly acidic solutions are stable at 0 °C for at least 2 weeks. Solutions are rapidly degraded upon heating and are very labile in alkaline solutions, especially in the presence of phosphate, maleate, or carbonate.
The last part of this sentence makes me think that phosphate or bicarbonate buffers would thus be inappropriate. I'm not sure why they say conflicting things, and they were not able to provide me with any further information.
They do confirm that neutral or slightly acidic pH should be fine for long-term storage.
