Abstract
Adenosine diphosphate-ribosyl cyclase (ADP-ribosyl cyclase) is a ubiquitous enzyme in eukaryotes that converts NAD + to cyclic-ADP-ribose (cADPR) and nicotinamide. A quantitative assay for cADPR was developed using capillary electrophoresis to separate NAD +, cADPR, ADP-ribose, and ADP with UV detection (254 nm). Using this assay, the apparent K m and V max for Aplysia ADP-ribosyl cyclase were determined to be 1.24 ± 0.05 mM and 131.8 ± 2.0 μM/min, respectively. Boric acid inhibited ADP-ribosyl cyclase non-competitively with a K i of 40.5 ± 0.5 mM. Boric acid binding to cADPR, determined by electrospray ionization mass spectrometry, was characterized by an apparent binding constant, K A, of 655 ± 99 L/mol at pH 10.3.
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