Monovalent carboxylic ionophores inhibit transport of carbamoyl-phosphate synthetase I into mitochondria in Reuber hepatoma H-35 cells and cause accumulation of enzyme precursor

Transport of the precursor for carbamoyl-phosphate synthetase I into mitochondria in Reuber hepatoma H-35 cells was inhibited by adding monensin or nigericin to the culture medium at a concentration of 0.5 microM, and the enzyme precursor accumulated, mainly in the cytosolic fraction. Accumulated precursor was degraded slowly with a half-life of more than 16 min. Valinomycin, nonactin, A23187, X-537A (lasalocid), bromo-lasalocid, and carbonyl cyanide m-chlorophenylhydrazone did not exhibit these effects at concentrations at which they did not inhibit protein synthesis of the cells.     

Antizyme to ornithine decarboxylase is present in the liver of starved rats.

Antizyme to ornithine decarboxylase (ODC) and ODC-antizyme complex were both present in liver cytosols of starved rats. The antizyme was identified by its molecular weight, kinetic properties, formation of a complex with ODC, and reversal of its inhibition by antizyme inhibitor. The average amount of antizyme in liver cytosols of starved rats was 0.1 unit/mg of protein, roughly corresponding to basal hepatic ODC activity in rats fed ad libitum. The presence of ODC-antizyme complex was detected by using antizyme inhibitor. These results indicate that antizyme participates in the regulation of ODC activity in vivo under physiological conditions.     

Pure Renin. Isolation from hog kidney and characterization.

The pressor enzyme renin (EC 3.4.99.19) was isolated in a pure and stable form from hog kidney by affinity chromatography on a pepstatin/agarose gel followed by three additional steps of conventional chromatography. Destruction of the enzyme by proteolysis during isolation was prevented by chemically eliminating proteases in extracts. The pure preparation was used for the characterization of this enzyme. Renin was found to be a glycoprotein containing glucosamine and possessing binding affinity to concanavalin A. Contrary to previous reports, pure renin is stable at neutral pH either at 4 or -20 degrees for 3 to 8 weeks. It has a molecular weight of 36,400 as determined by equilibrium ultracentrifugation, an isoelectric point of 5.2 and E1%1cm (280 nm) of 9.1. In contrast to crude preparations, the enzyme activity has a broad pH optimum between pH 5.5 and 7.0 for both hog angiotensinogen and the synthetic octapeptide substrate benzyloxycarbonyl-Pro-Phe-His-Leu-Leu-Val-Tyr-Ser-beta-naphthylamide. The rate of formation of angiotensin I from hog angiotensinogen at pH 6.0 and 37 degrees was 267 microng/h/microng of renin, or 2000 Goldblatt units/mg of renin. For the synthetic fluorogenic octapeptide substrate benzyloxycarbonyl-Pro-Phe-His-Leu-Leu-Val-Tyr-Ser-beta-naphthylamide, a Km of 33 micronM and a Vmax of 0.94 micronmol/h/mg of enzyme were obtained at pH 6.5 and 37 degrees.     

Modes of DNA replication primed with the oligomer of palindrome

What is the precise molecular mechanism of semi-conservative DNA replication? After the great efforts of the past 20 years, molecular biology has now established the discontinuous syntheses of daughter DNA on both of the parental strands. In order to explain this type of discontinuous replication, we introduce the concept of a palindromic primer.First we focus our attention on various oligomers (RNA or DNA) which appear usually or occasionally in the process of replication. Then we propose the palindromic nature of these oligomers so as to serve as the primer of DNA synthesis. This postulation gives a theoretical reasoning for the discontinuities of both new strands in the fork region of replication.Subsequently we consider Watson's concatemeric intermediate theory, proposed for the explanation of replicative synthesis of phage T7 DNA. By considering the contribution of some sequence-specific endonuclease(s), we suggest the existence of partial palindromic sequences of bases at the connecting region(s) in which the redundant ends of the respective phage DNA molecules are overlapping. Another theory on the replication of linear chromosomal DNA including the concept of the terminal palindromic sequence of bases is also analyzed from the viewpoint of palindromic primer. Further, some recent experimental approaches, especially on the origin(s) of DNA replication, are shown to favour the concept of a palindromic primer.     

Verdohemoglobin as a substrate for proteases is applicable to assays over a wide pH range.

Verdohemoglobin, a heme-modified derivative readily obtained by ascorbic acid-coupled oxidation of oxyhemoglobin, was found to be a suitable substrate for protease with which assay can be carried out at all pH values. The advantage of verdohemoglobin over such popular substrates as alkali-and-urea-denatured hemoglobin and casein was demonstrated by a pH-profile study with Pronase E.     

Effects of sodium tungstate on the nuclear uptake of glucocorticoid-receptor complex from rat liver

Effects of sodium tungstate on the nuclear uptake of rat liver cytosolic glucocorticoidreceptor complex were examined at pH 7. The nuclear uptake of heat-activated [³H]triamcinolone acetonide-receptor complex was blocked completely in the presence of 1 mm tungstate. A preincubation of nuclear preparation with tungstate (>0.1 mm) blocked the subsequent uptake of [³H]triamcinolone acetonide-receptor complex. When the tungstate-treated nuclear preparation was washed with 0.3 M KCl, its [³H]triamcinolone acetonide-receptor complex binding capacity recovered to 50% of that of control samples with no tungstate treatment. A preincubation of chromatin with tungstate yielded similar results. The nuclear-bound [³H]triamcinolone acetonide-receptor complex, formed either by an in vivo administration of [³H]triamcinolone acetonide or by an in vitro incubation of glucocorticoid-receptor complex with isolated nuclei, was extracted by tungstate in a concentration-dependent manner. The majority of nuclear-bound [³H]triamcinolone acetonide could be extracted with 0.1 and 1 mm tungstate from in vitro- and in vivo-labeled nuclei, respectively. The tungstate-extracted steroid-receptor complexes sedimented in 4–5 S and 3.3–3.5 S region in 10 mm KCl- and 0.3 mm KCl-containing sucrose gradients, respectively. Tungstate treatment caused an irreversible loss of the nuclear binding capacity of [³H]triamcinolone acetonide-receptor complex which could not be recovered after dialysis. These studies indicate that tungstate affects both glucocorticoidreceptor complex and certain nuclear or chromatin proteins.     

Modulation of somatostatin release by endogenous glucagon and insulin: physiological relationship between A, B and D cells in rat pancreatic islets

In order to understand the physiological role of endogenous insulin or glucagon in somatostatin release, isolated rat pancreatic islets were treated with antiinsulin or antiglucagon antiserum in the presence of physiological amounts of glucose. The release of somatostatin was unchanged by treatment with antiinsulin antiserum which neutralized insulin released by 3.3, 8.3 and 16.7 mM of glucose. However, somatostatin release after treatment with antiglucagon antiserum was much reduced at all concentrations of glucose when compared with the release from control serum. Exogenous rat insulin (0.11, 1.11 micrograms/ml) had no effect, but exogenous glucagon (1, 5 micrograms/ml) resulted in a significant increase. Somatostatin release was stimulated by glucose, but the effect was insignificant. These results clearly indicate the physiological role of endogenous glucagon in the modulation of somatostatin release from the islets of Langerhans. Furthermore, the physiological relationship between A, B and D cells may be mediated through the paracrine mechanism.     

Cloning and functional expression of a novel endoprotease involved in prohormone processing at dibasic sites.

We cloned and sequenced a cDNA from a library of mouse pituitary AtT-20 cells which are known to cleave an endogenous and various foreign prohormones at dibasic sites. This cDNA encodes a novel 753-residue protein, named PC3, which is structurally related to the yeast Kex2 protease involved in precursor cleavage at dibasic sites and to recently identified mammalian Kex2-like proteins, furin and PC2. Among examined cell lines and tissues, PC3 mRNA was only detected in AtT-20 cells. The substrate specificity of PC3 expressed in mammalian cells was similar to that observed in AtT-20 cells. We conclude that PC3 is a resident prohormone processing endoprotease in AtT-20 cells.