Specific isoprenyl group linked to transducin gamma-subunit is a determinant of its unique signaling properties among G-proteins

Among 11 subtypes of heterotrimeric G-protein gamma-subunit, gamma1 (rod), gamma8 (cone) and gamma11 are modified with farnesyl while the others are modified with geranylgeranyl at the C-terminus. To understand the role of specific isoprenylation (farnesylation) of retinal transducin, we examined how and to what extent the type of isoprenyl group affects transducin-beta gamma (beta1 gamma1) functions such as interactions with membranes, Galpha/receptor, and effectors. To this end, the C-terminal farnesylation signal sequence (CVIS) of gamma1 was replaced by a geranylgeranylation signal (CVIL), and the resultant mutant (S74L) or wild-type (WT) gamma1 was coexpressed with beta1 in the baculovirus-Tn5 insect cell system. Both gamma1WT and gamma1S74L expressed as a beta gamma complex were mixtures modified with farnesyl and geranylgeranyl groups. The ratio of farnesyl to geranylgeranyl in preparations of beta1 gamma1WT and beta1 gamma1S74L purified from the Tn5 cell membrane fraction was about 1:2 and 1:6, respectively. These two forms of recombinant beta1 gamma1 and retinal beta1 gamma1 were different in their abilities to associate with rod outer segment membranes with the following rank order: beta1 gamma1S74L > beta1 gamma1WT > retinal beta1 gamma1. Functionally, beta1 gamma1S74L was the most potent to promote pertussis toxin-catalyzed ADP ribosylation of transducin-alpha (Talpha), to stimulate metarhodopsin II-catalyzed GTPgammaS-binding reaction to Talpha and to modulate adenylyl cyclase and phospholipase C activities. All of the beta1 gamma1 functions absolutely required the isoprenylation of the gamma-subunit. As for the interaction with Goalpha and adenylyl cyclase, predominantly geranylgeranylated beta1 gamma1S74L was less effective than geranylgeranylated beta1 gamma2 purified from bovine brain. These results demonstrate that the properties of Gbeta gamma are strongly affected by the type of functionally indispensable isoprenylation in addition to the amino acid sequence of Ggamma. The relative contribution of the two factors depends on proteins with which Gbeta gamma interacts.     

A cause of the motion of arcs in the presence of a magnetic field

A cause of the retrograde motion of arcs in the magnetic field is explained by the gyromotion of ions which are produced in the arc column. It is shown that the mechanism is consistent with fundamental aspects of the retrograde motion.     

Graft copolymerization of glass fiber and its application

Modified glass fibers, containing unsaturated hydrocarbon surface groups, were prepared by a hydrothermal treatment, with allylglycidylether in excess as reagent. Graft polymerization of the treated glass fiber with styrene and methylmethacrylate was carried out in sealed tubes, under nitrogen, using benzoyl peroxide (BPO) and cumene hydroperoxide (CHPO) as initiators. When BPO was used as the initiator, the grafting efficiency was extremely low, but the graft copolymerization behavior was similar to that of usual organic polymers. With CHPO, both grafting ratio and grafting efficiency were very high. Various properties of composite materials containing grafted glass cloth were studied. Flexural strength, flexural modulus, and interlaminar shear strength increased proportionally to the increase of the grafting ratio; the same values were decreased only in a small extent after the boiling test.     

Mechanical properties of molybdenum neutron-irradiated at a high temperature

Molybdenum specimens prepared by two processes, powder-metallurgy (PM) and electron-beam melting (EB), were irradiated to a fast neutron fluence of 2.74 × 10²⁴n/m² (E_n? 1 MeV) at about 600°C (873 K), and their mechanical properties were studied in detail. It was shown that the degree of irradiation embrittlement in EB-Mo was smaller than that in PM-Mo, which might be caused by stronger grain-boundaries and probably smaller irradiation-hardening in the former. From the relation between the recovery of ductility and microstructural changes in post-irradiation annealed PM-Mo at 800 (1073 K), 1000 (1273 K) and 1200°C (1473 K), it was concluded that the recovery resulted from a decrease of irradiation hardening due to a rearrangement and a disappearance of depleted-zones, dislocation-loops and voids in order with increasing annealing temperature. An anomalous mode of fracture was observed in as-irradiated specimens, which consisted of inhomogeneous deformation, then brittle fracture not at the center but at the root of the deformation neck. This mode was observed in a narrow temperature range near the DBTT. A possible mechanism is discussed.     

Noncompetitive inhibition by L-cysteine and activation by L-glutamate of the iron-oxidizing activity of a mixotrophic iron-oxidizing bacterium strain OKM-9

A mesophilic, mixotrophic iron-oxidizing bacterium strain OKM-9 uses ferrous iron as a sole source of energy and L-glutamate as a sole source of cellular carbon. Uptake of L-glutamate into OKM-9 cells is absolutely dependent on ferrous iron oxidation. Thus, the Fe(2+)-dependent L-glutamate uptake system of strain OKM-9 is crucial for the bacterium to grow mixotrophically in iron medium with L-glutamate. The relationship between iron oxidation and L-glutamate transport activities was studied. Iron oxidase containing cytochrome a was purified 9-fold from the plasma membrane of OKM-9. A purified iron oxidase showed one rust-colored band following disc gel electrophoresis after incubation with Fe(2+). The Fe(2+)-dependent L-glutamate transport system was also purified 14.5-fold from the plasma membrane using the same purification steps as for iron oxidase. Fe(2+)-dependent L-glutamate and L-cysteine uptake activities of OKM-9 were 0.36 and 0.24 nmol/mg/min, respectively, when a concentration of 18 mM of these amino acids was used as a substrate. Both uptake activities were completely inhibited by potassium cyanide (KCN), suggesting that cytochrome a in the iron oxidase is involved in the transport process. The iron-oxidizing activity of strain OKM-9 was activated 1.7-fold by 80 mM L-glutamate. In contrast, the activity was noncompetitively inhibited by L-cysteine. The Michaelis constant of iron oxidase for Fe(2+) was 12.6 mM and the inhibition constant for L-cysteine was 41.6 mM. A marked inhibition of iron oxidase by 50 mM L-cysteine was completely reversed by the addition of 60 mM L-glutamate. The results suggest the possibility that iron oxidase has a binding site for L-cysteine and the cysteine first bound to the iron oxidase was replaced by the added L-glutamate.     

Multicolorings of Series-Parallel Graphs

Let G be a graph, and let each vertex v of G have a positive integer weight ω(v). A multicoloring of G is to assign each vertex v a set of ω(v) colors so that any pair of adjacent vertices receive disjoint sets of colors. This paper presents an algorithm to find a multicoloring of a given series-parallel graph G with the minimum number of colors in time O(n W), where n is the number of vertices and W is the maximum weight of vertices in G.     

Studies on synthetic-polymer plates with high surface energy. II. Diethylene glycol bis(allyl carbonate)–unsaturated carboxylic acid system

Polymer plates with high surface energy were prepared by the procedure described in the previous paper, using diethylene glycol bis(allyl carbonate) as a substrate polymer and acrylic acid or methacrylic acid as a hydrophilic monomer. By the alkali treatment (immersing in an aqueous 0.1N NaOH solution for 2 h), the resulting polymer plates had good water wettability (contact angle for water = 10°) and sufficient mar resistance (the scratching hardness = 45–50 g) in a dry state, and their clarities were higher than those for DAP systems previously reported. The surface densities of carboxyl groups on the polymer plate estimated by use of the McBain's equation were 0.18–0.46 molecule/Ų.