19F nuclear magnetic resonance studies of structure and function relationships in trifluoroacetonylated rabbit muscle glyceraldehyde-3-phosphate dehydrogenase.

Specific reaction of Cys-149 with 3,3,3-trifluorobromacetone allows one to probe symmetry relation between the active center regions of tetrameric glyceraldehyde-3-phosphate dehydrogenase by 19F nuclear magnetic resonance (nmr) techniques. Nmr titration studies in the pH range of greatest enzymic activity reveal the existence of species with an (alphaalpha')2 structure; this symmetry is not induced by the coenzyme. Addition of NADH to the ketone-labeled protein causes the enzymic reduction of the ligand in a stereospecific manner and is used to demonstrate the functionality of residues other than Cys-149 that are essential for catalysis.

Purified acetylcholine receptor: its reconstitution to a chemically excitable membrane.

Association of purified acetylcholine receptor from Torpedo californica electroplax with lipids from the same organism results in a vesicular membrane system in which the receptor protein is oriented so that all neurotoxin binding sites appear to be on the outer surface. The reconstituted system is chemically excitable by acetylcholine and carbamylcholine, as measured by (22)Na(+) efflux. This excitability is specifically blocked by the antagonist alpha-bungarotoxin.