Electron-microscopic studies on the threshold value of calcium concentration for the release of storage granules and the acceleration of their degradation in the rat parathyroid gland

Summary To determine both a threshold value of calcium concentration (CC) for the release of storage granules and that for the acceleration of degradation of these granules, the rat parathyroid glands were perfused in situ with HEPES-Ringer solutions containing different concentration of Ca²⁺ for 10 min. With perfusates containing 0.83–1.21 mM Ca²⁺ (equivalent to 8–11 mg/dl serum calcium), the number of type-I storage granules (large core) [NSG-I] and that of type-II storage granules (small core) [NSG-II] remained unchanged. With perfusates containing 0.83 mM Ca²⁺ (7.5 mg/dl) or less, however, both NSG-I and NSG-II decreased remarkably and the former was larger than the latter. On the contrary, with perfusates containing 1.27 mM Ca²⁺ (11.5 mg/dl) or more, NSG-II increased and the ratio of NSG-I to NSG-II was changed reversely. We concluded that a thereshold value of CC required for the release of storage granules may be present between 0.88 and 0.83 mM Ca²⁺ (8 and 7.5 mg/dl) and that a threshold value of CC for accelerating the transformation of type-I granules into type-II, the degradation of storage granules, may be situated at about 1.27 mM Ca²⁺ (11.5 mg/dl). Additionally, it was suggested that both prosecretory and storage granules are not only formed at the innermost Golgi cisterna but also at the trans-Golgi network.     

The spatial patterns of parasitism of eumenid wasps,Anterhynchium flavomarginatum andOrancistrocerus drewseni by the miltogrammine flyAmobia distorta

1. Spatial patterns of parasitism of eumenid wasps Anterhynchium flavomarginatum and Orancistrocerus drewseni by the miltogrammine fly Amobia distorta were studied in Kyoto, Japan during 1980–1984.
2. In generations of low (<5%) and medium (5–20%) parasitism, percent parasitism per shed (the habitat of the hosts) increased as a function of host density. Conversely, in generations of high (>20%) parasitism, percent parasitism was rather constant over different host densities.
3. The spatial distributions of adult miltogrammine flies among sheds were censused in generations of low and medium parasitism. The frequency of observations of adult miltogrammine flies was higher at sheds of higher host density (aggregative behavioral response), but on the other hand, the adult miltogrammine flies distributed in an underdispersed (or regular) manner in relation to other conspecifics.
4. The spatially density independent relationship between host density and percent parasitism in generations of high parasitism was explained in relation to parasitoid dispersal from patches of high parasitoid density.

     

Bacterial NADH-quinone oxidoreductases

The NADH-quinone oxidoreductases of the bacterial respiratory chain could be divided in two groups depending on whether they bear an energy-coupling site. Those enzymes that bear the coupling site are designated as NADH dehydrogenase 1 (NDH-1) and those that do not as NADH dehydrogenase 2 (NDH-2). All members of the NDH-1 group analyzed to date are multiple polypeptide enzymes and contain noncovalently bound FMN and iron-sulfur clusters as prosthetic groups. The NADH-ubiquinone-1 reductase activities of NDH-1 are inhibited by rotenone, capsaicin, and dicyclohexylcarbodiimide. The NDH-2 enzymes are generally single polypeptides and contain non-covalently bound FAD and no iron-sulfur clusters. The enzymatic activities of the NDH-2 are not affected by the above inhibitors for NDH-1. Recently, it has been found that both of these types of the NADH-quinone oxidoreductase are present in a single strain of bacteria. The significance of the occurrence of these two types of enzymes in a single organism has been discussed in this review.     

Carboxyl methylation and farnesylation of transducin gamma-subunit synergistically enhance its coupling with metarhodopsin II.

A heterotrimeric G-protein in vertebrate photoreceptor cells is called transducin (T alpha beta gamma), whose gamma-subunit is a mixture of two components, T gamma-1 and T gamma-2. T gamma-2 is S-farnesylated and partly carboxyl methylated at the C-terminal cysteine residue, whereas T gamma-1 lacks the modified cysteine residue. To elucidate the physiological significance of the double modifications in T gamma, we established a simple chromatographic procedure to isolate T gamma-1, methylated T gamma-2 and non-methylated T gamma-2 on a reversed phase column. Taking advantage of the high and reproducible yield of T gamma from the column, we analyzed the composition of T gamma subspecies in the T alpha-T beta gamma complex which did not bind with transducin-depleted rod outer segment membranes containing metarhodopsin II. The binding of T alpha-T beta gamma with the membranes was shown to require the S-farnesylated cysteine residue of T gamma, whose methylation further enhanced the binding. This synergistic effect was not evident when T alpha was either absent or converted to the GTP-bound form which is known to dissociate from T beta gamma. Thus we concluded that a formation of the ternary complex, T alpha-T beta gamma-metarhodopsin II, is enhanced by the farnesylation and methylation of T gamma. This suggests that the double modifications provide most efficient signal transduction in photoreceptor cells.     

Purification and characterization of a heat-stable enterotoxin of Vibrio mimicus

A heat-stable enterotoxin produced by Vibrio mimicus (VM-ST) was studied. VM-ST was purified from a culture supernatant of V. mimicus strain AQ-0915 by ammonium sulfate fractionation, hydroxyapatite treatment, ethanol extraction, column chromatography on both SP-Sephadex C-50 and DEAE-Sephadex A-25, and HPLC, and the recovery rate was about 15%. Purified VM-ST was heat-stable. VM-ST activity was cross-neutralized by anti-STh antiserum. The amino acid composition of the purified VM-ST was determined 17 amino acid residues in the following sequence: Ile-Asp-Cys-Cys-Glu-Ile-Cys-Cys-Asn-Pro-Ala-Cys-Phe-Gly-Cys-Leu-Asn. This composition and sequence were identical to those of V. cholerae non-O1-ST. These results clearly demonstrate the production of a characteristic VM-ST by V. mimicus.     

A new trisaccharide sugar chain linked to a serine residue in bovine blood coagulation factors VII and IX

A new trisaccharide sugar chain was identified in bovine blood coagulation factors VII and IX. A pentapeptide isolated from factor VII contained Ser-52, which could not be identified with a gas-phase sequencer, suggesting an unknown substituent on the serine residue (Takeya, H. et al. (1988) J. Biol. Chem., in press). The same results were obtained for a pentapeptide containing Ser-53 of factor IX. Component sugar analysis revealed that the peptide contained 1 mol of glucose and 2 mol of xylose. This sugar component was also confirmed by high-resolution fast atom bombardment mass spectrometric analysis of the pentapeptide. The trisaccharide was released from the peptides by means of beta-elimination reaction and its reducing end was coupled with 2-aminopyridine. The fluorescent pyridylamino (PA-) derivative of the trisaccharide was purified by gel-filtration and reversed-phase HPLC. The sugar composition of the PA-trisaccharide was found to be 2 mol of xylose and 1 mol of PA-glucose. These results indicate the existence of a (Xyl2)Glc-Ser structure in factors VII and IX.     

A single amino acid substitution converts cytochrome P450(14DM) to an inactive form, cytochrome P450SG1: complete primary structures deduced from cloned DNAS

Genes for lanosterol 14-demethylase, cytochrome P450(14DM), and a mutated inactive cytochrome P450SG1 were cloned from S. cerevisiae strains D587 and SG1, respectively. A single nucleotide change resulting in substitution of Asp for Gly-310 of cytochrome P450(14DM) was found to have occurred in cytochrome P450SG1. In this protein the 6th ligand to heme iron is a histidine residue instead of a water molecule, which may be the ligand for the active cytochrome P450(14DM). Molecular models of the active sites of the cytochrome P450(14DM) and cytochrome P450SG1 were built by computer modeling on the basis of the known structure of that of cytochrome P450CAM whose crystallographic data are available. The mechanisms which may cause a histidine residue to gain access to the heme iron are discussed.