Catalytic properties of the retinal rod outer segment disk ADP-ribosyl cyclase

Andrea Fabiano, Isabella Panfoli, Daniela Calzia, Maurizio Bruschi, Silvia Ravera, Angela Bachi, Angela Cattaneo, Alessandro Morelli, Giovanni Candiano

Research output: Contribution to journalArticlepeer-review


Cyclic ADP-ribose (cADPR) is a second messenger modulating intracellular calcium levels. We have previously described a cADPR-dependent calcium signaling pathway in bovine rod outer segments (ROS), where calcium ions play a pivotal role. ROS ADP-ribosyl cyclase (ADPR-cyclase) was localized in the membrane fraction. In the present work, we examined the properties of the disk ADPR-cyclase through the production of cyclic GDP-ribose from the NAD + analogue NGD+. The enzyme displayed an estimated Km for NGD+ of 12.5 ± 0.3 μM, a Vmax of 26.50 ± 0.70 pmol cyclic GDP-ribose synthesized/min/mg, and optimal pH of 6.5. The effect of divalent cations (Zn2+, Cu2+, and Ca2+) was also tested. Micromolar Zn2+ and Cu2+ inhibited the disk ADPR-cyclase activity (half maximal inhibitory concentration, IC50 = 1.1 and 3.6 μM, respectively). By contrast, Ca2+ ions had no effect. Interestingly, the properties of the intracellular membrane-associated ROS disk ADPR-cyclase are more similar to those of the ADPR-cyclase found in CD38-deficient mouse brain, than to those of CD38 or CD157. The novel intracellular mammalian ADPR-cyclase would elicit Ca2+ release from the disks at various rates in response to change in free Ca2+ concentrations, caused by light versus dark adaptation, in fact there was no difference in disk ADPR-cyclase activity in light or dark conditions. Data suggest that disk ADPR-cyclase may be a potential target of retinal toxicity of Zn2+ and may shed light to the role of Cu2+ and Zn 2+ deficiency in retina.

Original languageEnglish
Pages (from-to)121-128
Number of pages8
JournalVisual Neuroscience
Issue number2
Publication statusPublished - Mar 2011


  • ADPR-cyclase
  • Calcium ion
  • Cyclic ADP-ribose disks
  • NGD
  • Phototrasduction

ASJC Scopus subject areas

  • Sensory Systems
  • Physiology


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