The effect of haem ligands on the redox states of the hexa-haem nitrite reductase from Wolinella succinogenes.

The nitrite reductase of Wolinella succinogenes containing six covalently bound haem groups has one haem group that will not reduce fully in the presence of excess Na2S2O4. The effect of the extrinsic ligands CO and cyanide on the redox state of this haem was studied by e.p.r. and magnetic c.d. spectroscopy. It was found that both ligands increased the extent of reduction of this haem group, and that in the case of CO binding the level of reduction was correlated with the extent of CO saturation of the enzyme. Stopped-flow studies of the effect of cyanide binding on the rate of dithionite reduction showed that the rate of reduction of the ligand-binding site was increased in the presence of cyanide. This suggests that reduction of the haem groups at the active site is thermodynamically unfavourable in the absence of an extrinsic ligand. The role of the 'non-reducing' haem group and the effect of ligands on this centre and on the rate of reduction are discussed in relation to the reduction of nitrite by this enzyme.     

Studies on alpha-adrenergic activation of hepatic glucose output. Studies on role of calcium in alpha-adrenergic activation of phosphorylase.

The role of Ca2+ ions in alpha-adrenergic activation of hepatic phosphorylase was studied using isolated rat liver parenchymal cells. The activation of glucose release and phosphorylase by the alpha-adrenergic agonist phenylephrine was impaired in cells in which calcium was depleted by ethylene glycol bis(beta-aminoethyl ether)N,N'-tetraacetic acid (EGTA) treatment and restored by calcium addition, whereas the effects of a glycogenolytically equivalent concentration of glucagon on these processes were unaffected. EGTA treatment also reduced basal glucose release and phosphorylase alpha activity, but did not alter the level of cAMP or the protein kinase activity ratio (-cAMP/+cAMP) or impair viability as determined by trypan blue exclusion, ATP levels, or gluconeogenic rates. The effect of EGTA on basal phosphorylase and glucose output was also rapidly reversed by Ca2+, but not by other ions. Phenylephrine potentiated the ability of low concentrations of calcium to reactivate phosphorylase in EGTA-treated cells. The divalent cation inophore A23187 rapidly increased phosphorylase alpha and glucose output without altering the cAMP level, the protein kinase activity ratio, and the levels of ATP, ADP, or AMP, The effects of the ionophore were abolished in EGTA-treated cells and restored by calcium addition. Phenylephrine rapidly stimulated 45Ca uptake and exchange in hepatocytes, but did not affect the cell content of 45Ca at late time points. A glycogenolytically equivalent concentration of glucagon did not affect these processes, whereas higher concentrations were as effective as phenylephrine. The effect of phenylephrine on 45Ca uptake was blocked by the alpha-adrenergic antagonist phenoxybenzamine, was unaffected by the beta blocker propranolol, and was not mimicked by isoproterenol. The following conclusions are drawn: (a) alpha-adrenergic activation of phosphorylase and glucose release in hepatocytes is more dependent on calcium than is glucagon activation of these processes; (b) variations in liver cell calcium can regulate phosphorylase alpha levels and glycogenolysis; (c) calcium fluxes across the plasma membrane are stimulated more by phenylephrine than by a glycogenolytically equivalent concentration of glucagon. It is proposed that alpha-adrenergic agonists activate phosphorylase by increasing the cytosolic concentration of Ca2+ ions, thus stimulating phosphorylase kinase.     

Mechanism and contribution of the pentose phosphate cycle to glucose metabolism in epididymal fat tissue

1. Glucose 6-phosphate, fructose 6-phosphate and altroheptulose 7-phosphate are the major products formed non-oxidatively from ribose 5-phosphate by rat epididymal fat pad enzymes. 2. Arabinose 5-phosphate was detected among the reaction products and significant activity of the new enzyme of the L-type pentose pathway, D-glycero D-ido octulose 1,8-bisphosphate: D-altroheptulose 7-phosphotransferase was found. 3. The glucose moieties of glucose 1-phosphate, glucose 6-phosphate and glucose 1,6-bisphosphate were degraded and showed that epididymal fat pad enzymes relocate 14C from [2-14C]glucose into C-1, C-2, and C-3 of each hexose-phosphate. 4. The 14C-distribution patterns in the hexose-phosphates revealed that these intermediates were not in isotopic equilibrium and the rate of the transaldolase exchange reaction was relatively small. 5. The 14C-distribution data suggest that glucose 1-phosphate, rather than glucose 6-phosphate, is the first intermediate in the path of glycogen synthesis from glucose in this tissue. 6. The data provide the first proof of the mechanism of the pentose pathway in adipose tissue.     

应用气-质联用仪测定三种螺旋藻中的甾醇成分

应用GLC/MS联用仪对室内培养的钝顶螺旋藻(Spirulina platensis (Nordstedt) Geitler)、极大螺旋藻(S.maxima (Stechell & Gardiner) Geitler)和盐泽螺旋藻(S.subsalsa Oerst)的甾醇成分进行了测定。从钝顶螺旋藻和盐泽螺旋藻中共分出11个相同的甾醇组分:胆甾醇、胆甾烷醇、芸苔甾醇、麦角甾醇、海绵甾醇、菜子甾醇、豆甾醇、24-乙基-Δ~(5,7,22)-胆甾醇、β-谷甾醇、异岩藻甾醇和4α,23,24-三甲基Δ~(5,22)-胆甾醇;从极大螺旋藻中只分离出8个甾醇组分。其中胆甾醇含量最高。4α,23,24-三甲基-Δ~(5,22)-胆甾醇为蓝藻中首次报导。     

The relation of ligand binding to redox state in the hexa-heme nitrite reductase of Wolinella succinogenes.

Ligand binding reactions and the relation between redox state and ligand binding in the hexa-heme nitrite reductase of Wolinella succinogenes have been studied using laser flash photolysis. On a picosecond time scale, a rapid excursion was observed corresponding to the breaking and reforming of an iron histidine bond. With the CO derivative, a geminate reaction was observed with a rate of 3 ns-1. On a nanosecond time scale, no slower geminate reactions were observed. For the cyanide derivative, no geminate reactions were observed at either time scale. The second order reaction of CO with the enzyme had a time course consisting of two distinct components. This time course changed in form as the enzyme came to equilibrium with CO, and the slower rebinding component was replaced by a faster rebinding component. It is suggested that CO binding enhances reduction of a heme with an unusually low redox potential and opens the structure of the active site to allow a faster second order reaction of CO. The proportion of the geminate CO reaction was unchanged, consistent with changes relatively remote from the ligand binding site. The second order reactions of cyanide also showed that redox effects influence its rebinding reaction. Adding cyanide to the CO complex of nitrite reductase showed that the two ligands have distinct heme binding sites.     

A functional interpretation ofLactuceae (Compositae) pollen

Pollen morphology and ultrastructure inLactuceae pollen is considered in relation to the accomodation of volume changes, pollination biology and exine-held substances. Echinate pollen grains, such as those ofCatananche, are shown to accomodate volume changes by folding along the colpi and possibly by volume changes in the cavea. The different patterns of echinolophate pollen respond in different ways. Folding along the colpi is important inScorzonera andTragopogon and to a limited extent inCichorium andEpilasia whilst inScolymus the colpi are almost immobilized. Movements of the lacunar floors take over the harmomegathic function to compensate for lack of colpus mobility. Bulging of the intine at the apertures and changes in the size of the cavea may account for part of the volume change accomodated in any pollen type. Echinolophate pollen is interpreted as being a superior means of regulating volume changes with the most economical and mechanically efficient use of wall material which has evolved independently in several tribes ofCompositae.     

Cytoplasmic filaments and cellular wound healing in amoeba proteus

The flexibility and self-healing properties of animal cell surface membranes are well known. These properties have been best exploited in various micrurgical studies on living cells (2, 3), especially in amoebae (7, 20). During nuclear transplantation in amoebae, the hole in the membrane through which a nucleus passes can have a diameter of 20-30 μm, and yet such holes are quickly sealed, although some cytoplasm usually escapes during the transfer. While enucleating amoebae in previous studies, we found that if a very small portion of a nucleus was pushed through the membrane and exposed to the external medium, the amoeba expelled such a nucleus on its own accord. When this happened, a new membrane appeared to form around the embedded portion of the nucleus and no visible loss of cytoplasm occurred during nuclear extrusion. In the present study, we examined amoebae that were at different stages of expelling partially exposed nuclei, to follow the sequence of events during the apparent new membrane formation. Unexpectedly, we found that a new membrane is not formed around the nucleus from inside but a hole is sealed primarily by a constriction of the existing membrane, and that cytoplasmic filaments are responsible for the prevention of the loss of cytoplasm.