Mapping of antigenic sites to monoclonal antibodies on the primary structure of the F1-ATPase beta subunit from Escherichia coli: concealed amino-terminal region of the subunit in the F1.

To analyze relationships between the ternary and primary structures of the beta subunit of Escherichia coli F1 ATPase, we prepared two monoclonal antibodies beta 12 and beta 31 against the beta peptide. These antibodies bind to the beta subunit but do not bind to the F1 ATPase, resulting in no inhibition of the ATPase activities. Several different portions of the beta subunit peptide were prepared by constructing expression plasmids carrying the corresponding DNA segment of the beta subunit gene amplified by the polymerase chain reaction. Western blotting analysis using these peptides revealed that the antibodies bound to a peptide of 104 amino acid residues from the amino terminal end, which is outside the previously estimated catalytic domain between residues 140 and 350. These results indicated that the amino terminal portion of the maximal 104 residues is not exposed to the surface of the F1 ATPase. The binding spectrum of the antibodies to the subunit from various species including Vibrio alginolyticus and thermophilic bacterium PS3 indicated possible epitope sequences within the 104 residues. The ternary structure of the beta subunit, in terms of cleavage sites by endopeptidases, was analyzed using the antibodies. A 43-kDa peptide without binding ability to beta 12 and beta 31 appeared upon cleavage by lysyl endopeptidase. The results suggested that lysyl residues from around 70 to 100 from the amino terminus are exposed to the surface of the beta subunit.     

Conformational changes in the vicinity of the N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine attached to the specific thiol of sarcoplasmic reticulum Ca2+-ATPase throughout the catalytic cycle

In the previous experiment (Suzuki, H., Obara, M., Kuwayama, H., and Kanazawa, T. (1987) J. Biol. Chem. 262, 15448-15456), the Ca2+-ATPase of sarcoplasmic reticulum vesicles was labeled with N-iodoacetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine without a loss of the catalytic activity. The main labeled site was Cys674. A large monophasic fluorescence drop occurred upon ATP binding to the catalytic site of the Ca2+-activated enzyme in the presence of K+. The present results show that this fluorescence drop is biphasic in the absence of K+. The first and rapid phase of this drop accounts for most of the fluorescence drop. This phase reflects a conformational change in the enzyme.ATP complex. The second and slow phase, being much smaller than the first phase, coincides with phosphoenzyme (EP) isomerization from the ADP-sensitive form to the ADP-insensitive form. This phase disappears when accumulation of ADP-insensitive EP is inhibited by K+ or when EP isomerization is prevented by the N-ethylmaleimide treatment. These results show that this phase reflects a conformational change upon EP isomerization. When free Ca2+ is chelated after EP formation from ATP, the fluorescence intensity is restored to the initial level without Ca2+. This restoration coincides with EP decomposition. This suggests that the fluorescence restoration reflects a conformational change upon hydrolysis of ADP-insensitive EP. This probability is supported by the concurrent occurrence of the Pi-induced fluorescence drop and EP formation from Pi. The results demonstrate that the fluorescence drop upon ATP binding is predominant in the fluorescence change throughout the catalytic cycle.     

Multiple deletions in mitochondrial DNA at direct repeats of non-D-loop regions in cases of familial mitochondrial myopathy

Muscle mitochondrial DNAs from two brothers with mitochondrial myopathy associated with peripheral neuropathy had multiple deletions, most of which started in non-D-loop regions, unlike in an autosomal dominant mitochondrial myopathy (Zeviani, M. et al., Nature 339, 309 (1989)). The non-D-loop regions with deletions were amplified by the polymerase chain reaction and the resulting fragments were subcloned and then sequenced. At least 12 deletions of different lengths in different sites were found. However, all the deletions were flanked by short direct repeats (4-12 base pairs).     

Rabbit brain glucose transporter responds to insulin when expressed in insulin-sensitive Chinese hamster ovary cells

Transfection of Chinese hamster ovary cells with the expression vector containing rabbit brain HepG2-type glucose transporter cDNA resulted in a dramatic over-expression (approximately 10-fold) of glucose transporter as assessed by either immunoblotting with antipeptide antibody against rabbit brain glucose transporter or photoaffinity labeling with [3H]cytochalasin B. 2-Deoxyglucose uptake was also increased 4-fold in the transfected cells, while no increase in transport activity or transporter amount was observed in cells that were transfected with the expression vector alone without glucose transporter cDNA. Significantly, insulin (10(-7) M) increased 2-deoxyglucose uptake in both control and transfected cells, but the increased amount of the transported 2-deoxyglucose by insulin in the transfected cells was 4.2-fold greater than that in control cells, indicating that the expressed rabbit brain HepG2-type glucose transporter responded to insulin. In addition, we have recently demonstrated that the HepG2-type glucose transporter exists in rat adipocytes and responds to insulin in a fashion similar to a majority of other types of glucose transporters (Oka, Y., Asano, T., Shibasaki, Y., Kasuga, M., Kanazawa, Y., and Takaku, F. (1988) J. Biol. Chem. 263, 13432-13439). In contrast, insulin did not stimulate glucose transport activity in HepG2 cells or IM-9 lymphocytes that have a significant amount of the HepG2-type glucose transporter. Thus, the results in this study further support the notion that insulin regulation of glucose transport activity depends on a tissue-specific signaling mechanism.     

Glucocorticoids increase insulin binding and the amount of insulin-receptor mRNA in human cultured lymphocytes.

The effect of steroid hormones on insulin binding and the amount of insulin-receptor mRNA was examined in IM-9 lymphocytes. Cortisol and cortexolone, but not oestrogen, increased both the binding of insulin and the amount of insulin-receptor mRNA in a time- and dose-dependent manner. Cortisol was most potent, and induced a 2-fold increase in insulin binding and a 4-fold increase in mRNA. The elevation in binding was due to an increased number of insulin receptors at the cell surface. The increase in mRNA involved all four of the insulin-receptor mRNAs and could not be inhibited by cycloheximide. The cortisol-induced increase in mRNA was associated with a 3-4-fold increase in the synthesis of pro-receptor. The relative potency of the three steroids indicated that these effects were mediated by an interaction with the glucocorticoid receptor. The results of this study suggest that cortisol can increase the number of insulin receptors at the cell surface by increasing the amounts of insulin-receptor mRNA and the synthesis de novo of insulin receptors.     

Paramagnetic water-soluble metallofullerenes having the highest relaxivity for MRI contrast agents.

Water-soluble gadolinium (Gd) endohedral metallofullerenes have been synthesized as polyhydroxyl forms (Gd@C(82)(OH)(n)(), Gd-fullerenols) and their paramagnetic properties were evaluated by in vivo as well as in vitro for the novel magnetic resonance imaging (MRI) contrast agents for next generation. The in vitro water proton relaxivity, R(1) (the effect on 1/T(1)), of Gd-fullerenols is significantly higher (20-folds) than that of the commercial MRI contrast agent, Magnevist (gadolinium-diethylenetriaminepentaacetic acid, Gd-DTPA) at 1.0 T close to the common field of clinical MRI. This unusually high proton relaxivity of Gd-fullerenols leads to the highest signal enhancement at extremely lower Gd concentration in MRI studies. The strong signal was confirmed in vivo MRI at lung, liver, spleen, and kidney of CDF1 mice after i.v. administration of Gd-fullerenols at a dose of 5 micromol Gd/kg, which was 1/20 of the typical clinical dose (100 micromol Gd/kg) of Gd-DTPA.     

Very fine roots respond to soil depth: biomass allocation,morphology, and physiology in a broad-leaved temperate forest

Very fine roots (<0.5 mm in diameter) of forest trees may serve as better indicators of root function than the traditional category of <2 mm, but how these roots will exhibit the plasticity of species-specific traits in response to heterogeneous soil nutrients is unknown. Here, we examined the vertical distribution of biomass and morphological and physiological traits of fine roots across three narrow diameter classes (<0.5, 0.5–1.0, and 1.0–2.0 mm) of Quercus serrata and Ilex pedunculosa at five soil depths down to 50 cm in a broad-leaved temperate forest. In both species, biomass and the allocation of very fine roots were higher in the surface soil but lower below 10-cm soil depth compared to values for larger roots (0.5–2.0 mm). When we applied these diameter classes, only very fine roots of Q. serrata exhibited significant changes in specific root length (SRL; m g⁻¹) and root nitrogen (N) concentrations with soil depth, whereas the N concentrations only changed significantly in I. pedunculosa. The SRL and root N concentrations of larger roots in the two species did not significantly differ among soil depths. Thus, very fine roots may exhibit species-specific traits and change their potential for nutrient and water uptake in response to soil depth by plasticity in root biomass, the length, and the N in response to available resources.     

Slow transition of phosphoenzyme from ADP-sensitive to ADP-insensitive forms in solubilized Ca2+, Mg2+-ATPase of sarcoplasmic reticulum: evidence for retarded dissociation of Ca2+ from the phosphoenzyme.

Solubilized Ca²⁺, Mg²⁺-ATPase of sarcoplasmic reticulum was phosphorylated with ATP without added MgCl₂. The phosphoenzyme formed was ADP-sensitive. Ca²⁺ in the medium was chelated after phosphorylation. This induced a slow transition of the phosphoenzyme from ADP-sensitive to ADP-insensitive forms. The ADP-sensitivity was restored by subsequent addition of CaCl₂. These results showed that the transition was caused by dissociation of Ca²⁺ bound to the phosphoenzyme. Further observations indicated that, when Ca²⁺ in the medium was chelated, Ca²⁺ bound to the phosphoenzyme was dissociated much more slowly than Ca²⁺ bound to the dephosphoenzyme. This suggests a possible formation of the occluded form of the Ca²⁺-binding site in the phosphoenzyme.