Evidence for the proximity of a cysteinyl and a tyrosyl residue in the active site of 6-phosphogluconate dehydrogenase

The treatment of 6-phosphogluconate dehydrogenase from Candida utilis with dansyl chloride causes the modification of one amino acid residue per enzyme subunit and the inactivation of the enzyme. Either a cysteine or a tyrosine residue can be modified, depending on the pH of the reaction mixture. The dansyl residue can be transferred from one residue to the other suggesting that the two amino acid residues are close in the tridimensional structure of the active site of the enzyme.     

The effects of nonsuppressible insulin-like protein (NSILP) on cyclic nucleotide metabolism in rat liver.

Nonsuppressible insulin-like protein (NSILP), 100 ng/ml, inhibited cyclic AMP accumulation in rat liver, as stimulated by glucagon, 10^?7M, from 493 ± 12 to 183 ± 7 pmoles/gm tissue (p<0.001), but did not alter basal levels of cyclic AMP, 143 ± 2 pmoles/gm tissue. NSILP, 100 ng/ml, also inhibited cyclic AMP accumulation, stimulated by epinephrine, 5 × 10^?4M, from 387 ± 12 to 233 ± 9 pmoles/gm tissue. With 1 μM as substrate, NSILP, 100 ng/ml, increased cAMP-dependent phosphodiesterase activity in liver slices from 19.08 ± 0.18 to 24.94 ± 0.38 pmoles cAMP hydrolyzed/mg protein/min (p<0.001), but did not alter this enzyme activity in broken cell preparations of rat liver. Cyclic GMP levels in liver slices, 22.5 ± 0.3 pmoles/gm tissue, were increased by NSILP to 36.3 ± 0.5 pmoles/gm tissue (p<0.01). NSILP had no effect on adenylate cyclase activity. These changes, caused by NSILP in cyclic nucleotide metabolism in liver, resemble those described for insulin, and suggest that alterations in cyclic nucleotide levels in liver may be relevant to other hepatic effects of NSILP.     

Protease inhibitors inhibit production of protein I of the outer membrane in Escherichia coli

Effects of protease inhibitors on composition of newly synthesized protein were studied by pulse-labeling E. coli cells with [³H]leucine and analyzing the labeled proteins by sodium dodecylsulfate gel electrophoresis. In addition to tosyl-lysine chloromethylketone that had been studied previously, antipain, leupeptin and diisopropyl fluorophosphate all inhibited production of a major outer membrane protein, protein I. Synthesis of protein I was specifically inhibited by antipain or leupeptin in strain K12, whereas several other proteins were also affected in strain B. Protein synthesis in strain B was generally more sensitive to inhibition by antipain than that in strain K12.