Unifying mechanism for Aplysia ADP-ribosyl cyclase and CD38/NAD(+) glycohydrolases.
Highly purified Aplysia californica ADP-ribosyl cyclase was found to be a multifunctional enzyme. In addition to the known transformation of NAD(+) into cADP-ribose this enzyme is able to catalyse the solvolysis (hydrolysis and methanolysis) of cADP-ribose. This cADP-ribose hydrolase activity, which becomes detectable only at high concentrations of the enzyme, is amplified with analogues such as pyridine adenine dinucleotide, in which the cleavage rate of the pyridinium-ribose bond is much reduced compared with NAD(+). Although the specificity ratio V(max)/K(m) is in favour of NAD(+) by 4 orders of magnitude, this multifunctionality allowed us to propose a 'partitioning' reaction scheme for the Aplysia enzyme, similar to that established previously for mammalian CD38/NAD(+) glycohydrolases. This mechanism involves the formation of a single oxocarbenium-type intermediate that partitions to cADP-ribose and solvolytic products via competing pathways. In favour of this mechanism was the finding that the enzyme also catalysed the hydrolysis of NMN(+), a substrate that cannot undergo cyclization. The major difference between the mammalian and the invertebrate enzymes resides in their relative cyclization/hydrolysis rate-constant ratios, which dictate their respective yields of cADP-ribose (ADP-ribosyl cyclase activity) and ADP-ribose (NAD(+) glycohydrolase activity). For the Aplysia enzyme's catalysed transformation of NAD(+) we favour a mechanism where the formation of cADP-ribose precedes that of ADP-ribose; i.e. macroscopically the invertebrate ADP-ribosyl cyclase conforms to a sequential reaction pathway as a limiting form of the partitioning mechanism.
Cakir-Kiefer
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Laboratoire de Chimie Bioorganique, UMR 7514 CNRS-ULP, Faculté de Pharmacie, 74 route du Rhin, 67400 Strasbourg-Illkirch, France.
Muller-Steffner
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Schuber
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D036541:ADP-ribosyl Cyclase; D051997:ADP-ribosyl Cyclase 1; D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000737:chemistry* / Q000378:metabolism; D001048:Aplysia / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D000432:Methanol / Q000494:pharmacology; D008954:Models, Biological; D008956:Models, Chemical; D009243:NAD / Q000378:metabolism; D009244:NAD+ Nucleosidase / Q000737:chemistry* / Q000378:metabolism; D013997:Time Factors
D015703:Antigens, CD; D000943:Antigens, Differentiation; D009243:NAD; D000244:Adenosine Diphosphate; D036541:ADP-ribosyl Cyclase; D009244:NAD+ Nucleosidase; D051997:ADP-ribosyl Cyclase 1; D000432:Methanol