A method for fluorescence sensing of adenosine and alkaline phosphatase based on the inhibition of S-adenosylhomocysteine hydrolase activity.

This study presents a simple fluorescent method for the sensitive and selective detection of adenosine, based on adenosine inhibiting S-adenosylhomocysteine hydrolase (SAHH)-catalyzed hydrolysis of S-adenosylhomocysteine (SAH). Because of homocysteine (HCys) belonging to the thiol and amino groups, 2,3-naphthalenedicarboxaldehyde (NDA) can selectively react with HCys to form a 6-membered ring without the addition of nucleophiles. Electrospray ionization mass spectrometry was used to obtain the molecular mass of the resulting products, which is helpful in proposing the possible reaction mechanism between NDA and HCys. When SAHH catalyzed the cleavage of SAH, the generated HCys reacted with NDA to form highly fluorescent products with a quantum yield of 34%. The addition of adenosine to an SAH solution resulted in the inhibition of SAHH activity. Consequently, HCys production decreased with an increase in adenosine concentration. Under optimal NDA derivatization conditions, the SAHH-based probe showed a limit of detection (at a signal-to-noise ratio of 3) for adenosine of 0.3 μM. Selectivity of the SAHH-based probe is more than 100-fold for adenosine over any adenosine analog. We validated the applicability of this probe by determining adenosine concentration in urine samples. The SAHH-based probe was also used to evaluate the activity and inhibition of alkaline phosphatase, which can convert adenosine monophosphate to adenosine.