Molecular physiology of neuronal K-ATP channels (review).

ATP sensitive potassium (K-ATP) channels are widely expressed in many cell types including neurons. K-ATP channels are heteromeric membrane proteins that consist of two very different subunits: the pore-forming, two-transmembrane spanning potassium channel subunit (Kir6) and the regulatory, 17 transmembrane spanning sulphonylurea receptor (SUR). This ensemble--joined together in a 4:4 stoichiometry--endows this channel with a unique combination of functional properties. The open probability of K-ATP channels directly depends on the intracellular ATP/ADP levels allowing the channels to directly couple the metabolic state of a cell to its electrical activity. Here, recent progress on the molecular composition and functional diversity of neuronal K-ATP channels is reviewed. One is particular concerned with single-cell mRNA expression studies that give insight to the coexpression patterns of Kir6 and SUR isoforms in identified neurons. In addition, the physiological roles of neuronal K-ATP channels in glucose sensing and adapting neuronal activity to metabolic demands are discussed, as well as their emerging pathophysiological functions in acute brain ischemia and chronic neurodegenerative diseases.     

Evidence of the carboxymethylation of nascent peptide chains on ribosomes

Protein carboxymethylase from bovine anterior pituitary is found to be capable of carboxymethylating proteins in an in vitro protein synthesizing system which includes S-adenosyl-L-methionine-[¹⁴C methyl], wheat germ ribosomes and oviduct mRNA. Optimal carboxymethylation is inhibited by puromycin indicating the requirement for de novo protein synthesis. Ultracentrifugal profiles show that carboxymethylated proteins are associated with ribosomal absorption peaks. This is consistent with the carboxymethylation of proteins occurring on nascent peptide chains.