Atlantoaxial rotatory subluxation, congenital absence of the posterior arch of the atlas, and cerebral palsy: an unusual triad.

Posttraumatic chronic atlantoaxial rotatory subluxation and congenital absence of the posterior arch of the atlas are rare upper cervical spine abnormalities. The present case is that of a 4-year-old girl who had these two spinal disorders as well as spastic cerebral palsy. The interrelationship, if any, between these three conditions is unclear but presented an unusual diagnostic triad. A posterior spinal fusion between the occiput and third cervical vertebra was performed because of concern for upper cervical spine instability. The patient was immobilized in a halo vest, and a solid fusion occurred within 3 months. Preoperatively the child had never walked independently, but postoperatively, while wearing the halo vest, she was able to walk without external support, thus raising the suspicion of previous spinal instability. Fifteen months postoperatively she remains spastic but has a stable, orthotic-free, independent gait.

Binding of coenzyme and substrate and coenzyme analogues to 6-phosphogluconate dehydrogenase from sheep liver. An X-ray study at 0.6 nm resolution.

The analogues of the coenzyme NADP+, nicotinamide--8-bromo-adenine dinucleotide phosphate (Nbr8ADP+) and 3-iodopyridine--adenine dinucleotide phosphate (io3PdADP+), were prepared. Nbr8ADP+ was found to be active in the hydrogen transfer adn io3PdADP+ is a coenzyme competitive inhibitor for 6-phosphogluconate dehydrogenase. The binding of NADP+, NADPH and NADPH together with 6-phosphogluconate as well as that of both analogues to crystals of the enzyme 6-phosphogluconate dehydrogenase has been investigated at 0.6-nm resolution using difference electron density maps. The molecules bind in a similar position in a cleft in the enzyme subunit distant from the dimer interface. The orientation of the coenzyme in the site has been determined from the io3PdADP+ -NADP+ difference density. The ternary complex difference density extends beyond that of the nicotinamide moiety of the coenzyme and tentatively indicates substrate binding. No clear identification of the bromine atom of Nbr8ADP+ can be made. However, the analogue is bound more deeply in the cleft than is NADP+. The NADPH density is the most clearly defined and has thus been used to fit a molecular model using an interactive graphics system, checking for preferred geometry. A possible conformation is presented which is significantly different from that of NAD+ in the lactate dehydrogenase ternary complex.

The three dimensional structure of sheep liver 6-phosphogluconate dehydrogenase at 2.6 A resolution.

The three-dimensional structure of sheep liver 6-phosphogluconate dehydrogenase has been determined at 2.6 A resolution by X-ray crystallographic studies. The amino acid sequence of the enzyme is now known and can be fitted to a modified electron density map. Use of 6 A electron density maps and the results of chemical modification experiments allows description of the active site and identification of residues which may be implicated in the binding of co-enzyme and substrate.