Ability of GHTD-amide and analogs to enhance insulin activity through zinc chelation and dispersal of insulin oligomers

Kinetics of Cu(II) complexation by ATCUN/NTS and related peptides: a gold mine of novel ideas for copper biology

Cu(II)-peptide complexes are intensely studied as models for biological peptides and proteins and for their direct importance in copper homeostasis and dyshomeostasis in human diseases. In particular, high-affinity ATCUN/NTS (amino-terminal copper and nickel/N-terminal site) motifs present in proteins and peptides are considered as Cu(II) transport agents for copper delivery to cells. The information on the affinities and structures of such complexes derived from steady-state methods appears to be insufficient to resolve the mechanisms of copper trafficking, while kinetic studies have recently shown promise in explaining them. Stopped-flow experiments of Cu(II) complexation to ATCUN/NTS peptides revealed the presence of reaction steps with rates much slower than the diffusion limit due to the formation of novel intermediate species. Herein, the state of the field in Cu(II)-peptide kinetics is reviewed in the context of physiological data, leading to novel ideas in copper biology, together with the discussion of current methodological issues.

Proinsulin C-peptide potentiates the inhibitory action of insulin on glucose synthesis in primary cultured rabbit kidney-cortex tubules: Metabolic studies

Effects of equimolar concentrations of proinsulin C-peptide and insulin on glucose synthesis were studied in primary cultures of rabbit kidney-cortex tubules grown in the presence of alanine, glycerol, and octanoate. The rhodamine-labeled C-peptide entered renal tubular cells and localized in nuclei, both in the presence and absence of insulin; preincubations with the unlabeled compound inhibited internalization. C-peptide did not affect glucose formation when added alone but potentiated the inhibitory action of insulin by about 20% due to a decrease in flux through glucose-6-phosphate isomerase (GPI) and (or) glucose-6-phosphatase (G6Pase). GPI inhibition was caused by: (i) increased intracellular contents of fructose-1,6-bisphosphate and fructose-1-phosphate, inhibitors of the enzyme and (ii) reduced level of the phosphorylated GPI, which exhibits higher enzymatic activity in the presence of casein kinase 2. A decrease in flux through G6Pase, due to diminished import of G6P by G6P-transporter from the cytoplasm into endoplasmic reticulum lumen, is also suggested. The data show for the first time that in the presence of insulin and C-peptide, both GPI and G6P-ase may act as regulatory enzymes of renal gluconeogenic pathway.