Spectrophotometric assay of NADase-catalyzed reactions

Regulation of NAD+ glycohydrolase activity by NAD(+)-dependent auto-ADP-ribosylation

NAD+ glycohydrolase (NADase; EC 3.2.2.5) is an enzyme that catalyses hydrolysis of NAD+ to produce ADP-ribose and nicotinamide. Its physiological role and the regulation of its enzymic activity have not been fully elucidated. In the present study, the mechanism of self-inactivation of NADase by its substrate, NAD+, was investigated by using intact rabbit erythrocytes and purified NADase. Our results suggest that inactivation of NADase was due an auto-ADP-ribosylation reaction. ADP-ribosylated NADase of rabbit erythrocytes was deADP-ribosylated when incubated without NAD+, and thus enzyme activity was simultaneously restored. These findings suggest that reversible auto-ADP-ribosylation of NADase might regulate the enzyme's activity in vivo.

The expression, affinity purification and characterization of recombinant Pseudomonas exotoxin 40 (PE40) secreted from Escherichia coli

Procedures have been devised for producing high yields of purified recombinant PE40, a protein important for the development of the anti-AIDS therapeutic, sCD4-PE40. PE40 is a truncated form of the bacterial toxin, Pseudomonas exotoxin A; it lacks the cell-binding domain, but retains domains II and III that are involved in membrane translocation and inhibition of protein synthesis in eukaryotic cells. Expression vectors in Escherichia coli encoding PE40 synthesized the product as a soluble protein under control of the T7 promoter. The expression capabilities of transformants of E. coli BL21(DE3) were highly unstable. Expression levels (secreted and total) were evaluated in shake flasks and at the 10-1 scale at 27 degrees C and 37 degrees C, and following induction by IPTG or lactose. The cell-free media from the batch process was applied directly to a Cibacron blue F3GA-chromatographic medium and PE40 was eluted by nicotinamide in high yield and purity. This purification strategy was based on the structural similarity of the blue dye to NAD, a natural substrate for domain III of PE40. Green and red dye-ligand chromatography steps removed nicotinamide as well as minor residual E. coli proteins from PE40. Reversed-phase liquid chromatography peptide maps of purified PE40 were characterized by electrospray ionization mass spectrometry to determine the sequence and verify disulfide bonding.

A stopped-flow mixer device for a batch microcalorimeter application to NAD-NADase reaction

A new molded polypropylene, diamond-like carbon (DLC)-coated mixing cell has been developed for use in the batch microcalorimeter. Reagent volume can be varied from 25 microliters to 100 microliters. A 10 microcalorie reaction heat can be measured to 5%. Repeat reactions can be done as often as every 10 min for a fast reaction. Reactions can be started within 1 h or less after loading. A pre-equilibrator and a temperature-controlled syringe drive unit permit solutions to be stored at 4 degrees C while being run at any temperature from -20 degrees C to 40 degrees C. The kinetics and enthalpy of reaction of NAD-NADase have been measured. delta H is about 21 kcal/mol endothermic.