Plastid changes during the conversion of chloroplasts to chromoplasts in ripening tomatoes

Methods were developed for the isolation of plastids from mature green and ripening tomatoes (Lycopersicon esculentum Mill.) and purification by sucrose or Percoll density-gradient centrifugation. Assessment of the purity of preparations involved phase-contrast and electron microscopy, assays for marker enzymes and RNA extraction and analysis. Proteins were extracted from isolated plastids at different ripening stages and separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The profiles obtained from chloroplasts and chromoplasts showed many qualitative and quantitative differences. Labelling of proteins with [³⁵S]methionine in vivo showed that there was active protein synthesis throughout ripening, but there was a change in the plastid proteins made as ripening proceeded. The cellular location of synthesis of specific proteins has yet to be established.Abbreviations CS citrate synthase - EDTA ethylenediaminetetraacetic acid,-acetate - GAPDH NADP⁺-glyceraldehyde-3-phosphate dehydrogenase - rRNA ribosomal RNA - SDS sodium dodecyl sulphate - SDS-PAGE SDS-polyacrylamide gel electrophoresis - Tris 2-amino-2(hydroxymethyl)-1,3-propanediol     

Solvent influence on rate and mechanism of oxidation of ethylenediaminetetraacetatocobaltate(II) by periodate

The kinetics of the oxidation of Co^II(EDTA)²⁻ by IO₄⁻ were studied in various ethanol + water mixtures covering the range 7.9 to 58.0 wt% ethanol, at five different temperatures in the range 15–35 °C. The effect of solvent on the rate and mechanism of the reaction was investigated. An inner-sphere mechanism for the reaction was proposed and supported by the calculated activation parameters.     

Proton nuclear magnetic resonance study of N,N-diethylformamide exchange on (N,N-diethylformamide)2,2′2″-tris(dimethylamino)triethylamine)cobalt(II) and its copper(II) analogue

Proton NMR studies of N,N-diethylformamide (def) exchange on [M(Me₆tren)def]²⁺ where M = Co and Cu yield: k_ex (298.2K) = 26.3 ± 2.2, 980 ± 70 s⁻¹; ΔH^≠ = 58.3 ± 1.7, 36.3 ± 0.9 kJ mol⁻¹; ΔS^≠= −22.2 ± 4.6, −65.9 ± 2.5 J K⁻¹ mol⁻¹; and ΔV^≠ = −1.3 ± 0.2, 5.3 ± 0.3 cm³ mol⁻¹ respectively. These data which are consistent with a and d activation modes operating when M = Co and Cu respectively are compared with data for related systems.     

The synthesis of some polyether bridged diphosphines and their reaction with Rh(COD)acac

The polyether bridged diphosphines,

(n = 1,2) have been prepared in 60–70% yield by reduction of the corresponding diphosphinedioxides with Si₂Cl₆ or (i-Bu)₂AlH. These diphosphinedioxides have been prepared in 75–90% yield by reaction of two equivalents of the appropriate

with one equivalent of di- and triethylene glycol ditosylate.In general, reaction between the diphosphines, Rh(COD)acac and HClO₄ gives a mixture of species, cis-[Rh(COD)($\text{PP}$)] [ClO₄] being the main complex. This complex reacts with CO to η³-trans- [$\text{Rh(CO)(}\text{PO}$$\text{P}$)] [ClO₄].     

Stability enhancement and circular dichroism spectral anomaly as an indication of non-covalent interactions in histidine- and tyrosine-containing ternary copper(II)—amino acid systems

Visible absorption and CD spectral and potentiometric studies on the His- and Tyr-containing ternary copper(II) complexes Cu(A)(L-B), where A refers to L-His, D-His, or L-Tyr and B to Lys, Tyr, Trp, Phe, Ala, Val, Arg, Glu, Asn, Gln, Ser, or Thr, were made to study ligand-ligand interactions in the complexes. While the CD spectral magnitudes in the d—d region are additive in the absence of side chain interactions and can be estimated from the magnitudes for the ternary systems involving DL-A or DL-B, deviation from the additivity was observed for Cu(L-His)(L-B) (B = LysH, Tyr, Trp, or Phe) and Cu(L-Tyr)(L-Trp). From the stability constants determined at 25 °C and I = 0.1 M (KNO₃), the equilibrium constants, K, for the following hypothetical equilibria were calculated to be large (0.14–0.60) for formation of Cu(L-/D-His)(L-B)(B = Tyr or Trp) and Cu(D-His)(L-Phe) with Cu(en)(L-Ala) as standard: $Cu(A)(L?Ala)+Cu(en)(L?b)\stackrel{K}{?}Cu(A)(L?B)+Cu(en)(L?Ala)$ The positive values indicate the stabilization due to the stacking between the imidazole ring of His and the aromatic side chain of L-B. Solvent dependence of the CD spectra for Cu(L-His)(L-LysH) and Cu(L-His) L-Trp) further supported the existence of the intramolecular electrostatic and hydrophobic interactions.     

Axial ligation of nitrogenous bases to five-coordinate chloro-meso-tetraphenylporphyrinatochromium(III)

The axial ligations of nitrogenous bases to the five-coordinate chloro-meso-tetraphenylporphyrinatochromium(III) [Cr(III)(TPP)(Cl)] were studied in a non-coordinating solvent, dichloromethane (CH₂Cl₂), by spectrophotometric methods. A correlation exists between log K for the axial ligation:

and pK_a for the N-donor ligand. This correlation suggests that ligand to metal σ bonding contributes to the complex formation, rather than does metal to ligand π back-donation.     

Tetrakis-[1-methylimidazoline-2(3H)-thione]-μ2-[1-methylimidazoline- 2(3H)-thione]-Di-Copper(I) sulphate trihydrate: Preparation, thermal analysis and crystal structure

1-emthylimidazoline-2(3H)-thione (mimtH) reacts with copper(II) sulphate pentahydrate in aqueous acetone to produce the dinuclear complex, Cu₂(mimtH)₅SO₄ · 3H₂O; the formula has been established by a combination of chemical and thermal analysis. The monoclinic crystals, (space group P_c, Z = 2), contain dinuclear cations, sulphate ions and water molecules. The dinuclear cation, Cu₂(mimtH)₅²⁺, consists of two trigonal copper(I) atoms, four terminal, monodentate, S-donating mimtH molecules and one S-bridging (μ₂) mimtH molecule. Some average dimensions are:Cu---S, 2.258 Å and S---Cu---S, 120.0°; the Cu---S---Cu bridging angle is 94.8° and the Cu---Cu separation distance is 3.308 Å.     

The concept of a changing receptor concentration: implications for the theory of drug action

Drugs are considered to produce their effects on biological tissues either by altering some physical property of cells or by interacting with specific cellular components, called receptors. Most drugs and endogenous neurotransmitters act on highly selective receptors located on the outer surface membrane of cells. These receptors were believed, until recently, to be stationary on the cell surface and to be present in unvarying numbers. Consequently, most early theorists modeled the drug-receptor interaction on the basis of stationary and static receptor molecules. The substantial advances in our understanding of drug action based on these models have partly justified this view. However, recent electron microscopic studies have revealed the presence of structures, including "coated" pits and vesicles, that appear to provide a mechanism by which cell surface receptors might be internalized in a process of endocytosis. The precise intracellular fate of these internalized receptors is unknown, but based on present understanding, it seems reasonable to believe that some are destroyed intracellularly whereas others are recycled to the cell surface. The importance of such processes to pharmacologic theory is a new awareness of a cellular pathway that is capable of internalizing drugs, receptors, or both. The implications of such a process to the theory of drug action extends to some unexplained drug phenomena such as down regulation, drug tolerance, tachyphyllaxis, and partial agonism. We present herein the theoretical framework for a model of drug action that incorporates the possibility of receptor internalization and subsequent degradation, recycling, or replacement.     

Reaction of some antiinflammatory 17 beta-(2-aminooxazol-4-yl) steroids with hydrogen peroxide. Synthesis of steroid-17-spiro-5'-oxazolidine-2',4'-diones

The heterocyclic moiety of 17 beta-(2-aminooxazol-4-yl) steroids is sensitive to the oxidizing action of hydrogen peroxide and yields products mainly from the opening of the amino-oxazole ring. Unlike simple 2-aminooxazoles, it does not rearrange to 2-imidazolone and the expected steroidal hydroperoxyimidazolidinones were not detected. Among the substances we isolated, N-(aminocarbonyl)-17 alpha-hydroxy-17-carboxamides (2a) and (3a) undergo spontaneous cyclization, in the reaction conditions, giving steroid-17-spirooxazolidinediones (2d) and (3d). Spirane (2d) was synthesized in high yields from (2a) in strongly alkaline medium.     

Erythrocyte cytosolic free Ca2+ and plasma membrane Ca2+-ATPase activity in cystic fibrosis

The properties of the Ca2+, Mg2+-ATPase of erythrocyte membranes from patients with cystic fibrosis (CF) were extensively compared to that of healthy controls. Following removal of an endogenous membrane inhibitor of the ATPase, activation of the enzyme by Ca2+, calmodulin, limited tryptic digestion or oleic acid, as well as inhibition by trifluoperazine, were studied. The only properties found to be significantly different (CF cells vs controls) were calmodulin-stimulated peak activity (90 vs 101, P less than 0.02) and trypsin-activated peak activity (92 vs 102, P less than 0.02). No significant difference could be measured in the steady-state Ca2+-dependent phosphorylation of CF and control erythrocyte membranes indicating similar numbers of enzyme molecules per cell. The functional state of Ca2+ homeostasis in intact erythrocytes was investigated by measuring the resting cytosolic free Ca2+ levels using quin-2. Both CF and control erythrocytes maintained cytosolic free Ca2+ between 20 to 30 nM. Addition of 50 uM trifluoperazine resulted in an increase in erythrocyte cytosolic free Ca2+ to about 50 nM in both CF and control cells. Estimates of erythrocyte membrane permeability using the steady-state uptake of 45Ca into intact erythrocytes revealed no differences between CF and control cells. These results confirm that there is a small decrease in the calmodulin-stimulated activity of the erythrocyte Ca2+, Mg2+-ATPase in CF. However, this deficit is apparently not large enough to impair the ability of the CF erythrocyte to maintain normal resting levels of cytosolic free Ca2+.