Actin paracrystal in the acrosome of newt sperm

When a newt sperm-head was treated with trypsin and DNase, an arrow-like thin rod was revealed. This rod presumably corresponds to the ‘perforatorium’ described by Picheral [1, 2] in Pleurodele sperm. It consisted of one apical and one caudal part. In the apical part there appeared to be an envelope with a 530 Å structural repeat, inside which coursed a filament bundle, presumably identical with that in the caudal part. In the caudal part, a characteristic filament bundle, quite similar to the paracrystal of rabbit skeletal actin [3], was observed after extensive treatment with trypsin. The optical diffraction pattern of this bundle indicates that it has the same helical symmetry as that of rabbit skeletal actin [4] but slightly different from that of the acrosomal process of Limulus sperm [5]. The diffraction pattern frequently has a strong meridional reflection at about (27 Å)⁻¹, which is usually observed only with low intensity in the actin paracrystals. This fact suggests that the structural unit in the bundle has a shape considerably different from that of the usual G-actin.     

Water and ion permeability of a native collagen membrane

With the help of a ribonucleoprotein it is possible to precipitate collagen in a layer of fibers with a 700 Å period. As collagen is a constituent of many membrane systems in the body, it seemed interesting to investigate the permeability of ions and water through a native collagen membrane.The experiments were carried out with the help of an acryl glass apparatus, where an osmotic pressure, a hydrostatic pressure difference or both can be maintained between the two bulk phases separated by the membrane. The diffusion coefficients for NaCl and KCl were found to be comparable with those in other biological membranes (D_s = 9 · 10⁻⁷cm² · s⁻¹) whereas there is difference of more than three orders of magnitude in the hydraulic permeability (L_p = 6 cm⁴ · J⁻¹ · s⁻¹).Volume flow measurements caused by an osmotic gradient indicated that the reflection coefficient for NaCl and KCl is very small. In hydrostatic pressure experiments, the membrane shows a preferred direction for volume flows which seems to have something to do with the mode of preparation of the membrane.     

Synthesis and crystal structure of a complex between lanthanum nitrate and a bicyclic polyether

Reaction between lanthanum nitrate hexahydrate and a macrobicyclic polyether in ethanol has yielded a product of overall stoichiometry 3:2. The ligand, 21R, 26S, 29R, 34S-21, 22, 23, 24, 25, 26, 29, 30, 31,32,33, 34-dodecahydro-1,4,7,14,17,20,28,35-octaoxa (2^3,29syn2^18,34syn) (7.7) orthocyclophane, L, provides 8 oxygen donor atoms. Crystals were obtained from MeOH/EtOH (50/50). Crystal structure determination on 9590 observations, R=0.059, has shown the triclinic unit cell, a = 26.562(6), b = 13.486(3), c = 12.154(3) Å, α=63.9(1), β = 100.0(1), γ = 102.0(1)° space group P , V = 3806 Å to contain, as the asymmetric unit, two complex cations (La(NO₃)₂L)⁺ and one complex anion (La- (NO₃)₅MeOH)²⁻. The lanthanum is 11-coordinated in the anion and one of the cations, in which there is one bidentate and one monodentate nitrate anion and 12-coordinated in the other cation. For the monodentate nitrate La---O = 2.448(9) Å, all other nitrate ions are bidentate (La---O = 2.594(9)−2.743(10) Å). Most La---O bonds are shorter in the 11 than in the 12-coordinated cation. There are large differences in La---O bond lengths according to the nature of the carbon atoms to which the oxygen is attached. The methanol molecule forms a hydrogen bond to one oxygen atom of the monodentate nitrate group.     

Heterocyclic compounds containing antimony 1. Synthesis, physicochemical properties, crystal and molecular structure of 2-(β-hydroxyethylthio) 1,3,2-oxathiastibolane

The compound (HOCH₂CH₂S) ) (1) has been prepared by the reaction of antimony(III) isopropoxide and 2-mercaptoethanol in a 1:2 molar ratio. Reaction of 1 with MOCH₃ (where M = Li, Na and K) yields bimetallic products of the type, M[(OCH₂CH₂S) )]. All these derivatives have been characterized by elemental analysis, IR, NMR (¹H and ¹³C) spectra and molar conductivity measurements. Crystals of 1 are triclinic, space group P , with a = 6.449(2), b = 10.285(2), c = 13.494(1) Å, α = 78.08(1), β = 75.99(1), γ = 71.54(2)°, V = 815.48 ų, Z = 4, D_calc = 2.239 g cm⁻³, (Mo Kα) λ = 0.7107 Å, μ = 3.55 mm₋₁, F(000) = 528, T = 295 K, final R = 0.0189 for 2344 reflections. One of the two mercaptoethanol moieties in 1 forms a five-membered chelate ring with antimony, Sb(1)---O(11) = 2.023(2) Å and Sb(1)---S(11) = 2.434(1) Å, while the other is bonded through the S atom only, Sb(1)---S(12) = 2.434(1) Å. The angles between these primary bonds with a mean value of 90.2° suggest a basically pyramidal, or pseudo tetrahedral structure if the stereochemically active lone pair is included in the coordination sphere. Two molecules are linked by intermolecular hydrogen bridges. The presence of weak intermolecular secondary bonding, Sb(1)---O(12) = 2.567(3) Å, in the complex indicates that the overall coordination polyhedron is best described in terms of a distorted trigonal bipyramidal arrangement.     

Synthesis of [Tl4Se16]: a novel tetranuclear Tl polyselenide

(Ph₄P)₄[Tl₄Se₁₆] was prepared hydrothermally in a sealed pyrex tube by the reaction of TlCl, K₂Se₄ and Ph₄PCl in a 1:1:1 molar ratio at 110 °C for one day. The red crystals were obtained in 50% yield. Crystals of (Ph₄P)₄[Tl₄Se₁₆]: triclinic P (No. 2), Z=1, a=12.054(9), b=19.450(10), c=11.799(6) Å, α=104.63(4), β=98.86(6), γ=101.99(6)° and V=2555(3) ų at 23 °C, 2θ_max=40.0°, μ=120.7 cm⁻¹, D_calc=2.23. The structure was solved by direct methods. Number of data collected: 5206. Number of unique data having F_o²>3σ(F_o²): 1723. Final R=0.075 and R_w=0.089. [Tl₄Se₁₆]⁴⁻ consists of four, almost already linearly arranged, tetrahedral thallium centers which are coordinated by two chelating Se₄²⁻, two bridging Se₂²⁻ and four bridging Se²⁻ ligands. [Tl₄Se₁₆]⁴⁻ sits on an inversion center and possesses a central {Tl₂Se₂}²⁺ planar core. The Tl(1)–Tl(1)′ distance in this core is 3.583(6) Å. These two thallium atoms are then each linked to two cyclic Tl(Se₄) fragments via bridging Se₂²⁻ and Se²⁻ ligands forming Tl₂Se(Se₂) five-membered rings.     

Synthesis and structure of an organosamarium aryloxide complex, (C5 Me5)2 Sm(OC6HMe4-2,3,5,6)

Bis(pentamethylcyclopentadienyl)samarium bis- (tetrahydrofuranate), (C₅Me₅)₂Sm(THF)₂, reacts with 2,3,5,6-tetramethylphenol in toluene to yield (C₅Me₅)₂Sm(OC₆HMe₄-2,3,5,6). The compound crystallizes in the space group P2₁/c with a = 8.725(3) Å, b=18.821(6) Å, c=18.461(6) Å, β= 111.17(2)°, V = 2827(2) ų and D_c=1.340 g cm⁻³ for Z = 4. Molecules of the aryloxide complex are monomeric and exhibit a bent metallocene structure with a nearly linear Sm---O---C(aryloxide) linkage: Sm---O = 2.13(1) Å, O---C = 1.29(2) Å, and Sm---O---C = 172.3(13)°. Reaction of the samarium complex with phenyllithium produces the previously- characterized species (C₅Me₅)₂Sm(C₆H₅)(THF).     

Permeability of bilayer lipid membranes for superoxide (O2) radicals

Egg yolk phosphatidylcholine monolamellar liposomes (1000 Å in diameter) loaded with cytochrome c were placed into an external solution, in which superoxide radicals, O₂⁻, were generated by a xanthine-xanthine oxidase system. The penetration of the superoxide radicals across the liposomal membrane was detected by cytochrome c reduction in the inner liposome compartment. The effects of modifiers and temperature on this process were studied. The permeability of liposomal membrane for O₂⁻(P′_O2⁻ = (7.6 ± 0.3) · 10^-8 cm/s), or HO₂^• (P′_HO2⁻ = 4.9 · 10^-4 cm/s) were determined. The effect of the transmembrane electric potential (K⁺ concentration gradient, valinomycin) on the permeability of liposomal membranes for O₂⁻ were investigated. It was found that O₂⁻ can penetrate across liposomal membrane in an uncharged form. The feasibility of penetration of superoxide radicals through liposomal membrane, predominantly via anionic channels, was demonstrated by the use of an intramolecular cholesterol-amphotericin B complex.     

Synthesis and crystal structure of the MgCl2(CH3COOC2H5)2· (CH3COOC2H5) adduct

The reaction of α-MgCl₂ with boiling ethyl acetate affords MgCI₂(CH₃COOC₂H₅)₂· (CH₃COOC₂H₅), which is obtained as crystals suitable for X-ray analysis only from the mother liquor. M=315.5, orthorhombic, space group P2₁22₁ (No. 18), a=25.077(3), b=8.616(1), c=7.345(1) Å, V=1587.0(3) ų, Z=4, D_x=1.32 g cm⁻³,λ A(Mo Kα)=0.71069 Å, μ=4.17 cm⁻¹, F(000)=664, T=298 K, observed reflections: 1667, R=0.059 and R_w=0.069. The structure is composed of polymeric chains of MgCl₂(CH₃COOC₂H₅₎₂ and the ethyl acetate molecules occupy a mutually trans position.     

The structures of bis(1H,5H-S-methylisothiocarbonohydrazidium) di-μ-chloro-octachlorodibismuthate(III) tetrahydrate and tris(1H-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III)

The structures of bis(1H⁺,5H⁺-S-methylisothiocarbonohydrazidium) di-μ-chlorooctachlorodibismuthate(III) tetrahydrate: (C₂H₁₀N₄S)₂(Bi₂Cl₁₀)· 4H₂O (compound [I]) and of tris(1H⁺-S-methylisothiocarbonohydrazidium) esachlorobismuthate(III): (C₂H₉N₄S)₃(BiCl_5.67I_0.33) (compound [II]) were determined from single crystal X-ray diffractometer data. Both compounds crystallize as triclinic (P ); crystals [I] with Z = 1 formula unit in a cell of constants: A = 10.621(3), B = 9.989(5), C = 7.439(3) Å, α = 88.31(2), β = 84.51(2), γ = 68.88(2)°, final R = 0.0427 for 2229 unique reflections with I 2σ(I); crystals [II] with Z = 2 and cell dimensions: A = 14.109(4), B = 12.209(9), C = 8.206(7) Å, α = 103.54(3), β = 104.95(2), γ = 81.96(2)°, final R = 0.0411 for 3637 unique reflections (1 2σ(I)). The structure of [I] is built up of diprotonated organic cations, water molecules and dinuclear centrosymmetric [Bi₂Cl₁₀]⁴⁻ anions held together by N-HCl, N-HO, O-HCl hydrogen bonds and Van der Waals interactions. The [Bi₂Cl₁₀]⁴⁻ complex consists of two edge-sharing octahedra in which three pairs of bonds of similar length are observed (Bi-Cl_av = 2.602(5), 2.712(4), 2.855(5) Å). The structure of [II] consists of monoprotonated cations and [BiCl_5.67I_0.33]³⁻ anions held together by a tridimensional network of hydrogen bonds. Each bismuth atom is octahedrally surrounded by six chlorine atoms, one of which is statistically substituted by a iodine atom.     

Technetium and rhenium complexes of mercapto-containing peptides 1. Tc(V) and Re(V) complexes with mercaptoacetyl diglycine (MAG2) and X-ray structure of AsPh4[TcO(MAG2)]·C2H5OH

The reaction of mercaptoacetyl diglycine (MAG₂) with technetium(V) gluconate in aqueous solution produced [TcO(MAG₂)]⁻. A single X-ray structure determination was carried out for the tetraphenylarsonium salt. The dark brown crystals are monoclinic, space group P2(1)/n, with a=12.478(5), b=14.922(5), c=17.183(9) Å and Z=4. The [TcO(MAG₂)]⁻ ion has a square pyramidal geometry with the technetium atom displaced by 0.756 Å towards the oxo ligand from the plane formed by the equatorial S,N,N,O atoms. The rhenium complex AsPh₄[ReO(MAG₂)] was prepared analogously starting from Re(V) gluconate and characterized.     

Synthesis and magnetic properties of bis(μ-hydroxo)bis[(2,2 ′-bipyridyl)copper(II)] squarate. Crystal structure of bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] squarate tetrahydrate

The compound [Cu₂(bipy)₂(OH)₂](C₄O₄)·5.5H₂O, where bipy and C₄O₄²⁻ correspond to 2,2′-bipyridyl and squarate (dianion of 3,4-dihydroxy-3-cyclo- butene-1,3-dione) respectively, has been synthesized. Its magnetic properties have been investigated in the 2–300 K temperature range. The ground state is a spin-triplet state, with a singlet-triplet separation of 145 cm⁻¹. The EPR powder spectrum confirms the nature of the ground state.Well-formed single crystals of the tetrahydrate, [Cu₂(bipy)₂(OH)₂](C₄O₄)·4H₂O, were grown from aqueous solutions and characterized by X-ray diffraction. The system is triclinic, space group P , with a = 9.022(2), b = 9.040(2), c = 8.409(2) Å, α = 103.51(2), β = 103.42(3), γ = 103.37(2)°, V = 642.9(3) ų, Z = 1, D_x = 1.699 g cm⁻³, μ(Mo Kα) = 17.208 cm⁻¹, F(000) = 336 and T= 295 K. A total of 2251 data were collected over the range 1θ25°; of these, 1993 (independent and with I3σ(I)) were used in the structural analysis. The final R and R_w residuals were 0.034 and 0.038 respectively. The structure contains squarato-O¹, O³-bridged bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] units forming zigzag one-dimensional chains. Each copper atom is in a square-pyramidal environment with the two nitrogen atoms of 2,2′-bipyridyl and the two oxygen atoms of the hydroxo groups building the basal plane and another oxygen atom of the squarate lying in the apical position.The magnetic properties are discussed in the light of spectral and structural data and compared with the reported ones for other bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] complexes.     

Type IIβ Regulatory Subunit of cAMP-Dependent Protein Kinase: Purification Strategies to Optimize Crystallization

To elucidate the structural basis for important differences between types I and II regulatory subunit isoforms (RI and RII) of adenosine 3′,5′-cyclic monophosphate (cAMP)-dependent protein kinase, the full-length RIIβ isoform and five RIIβ deletion mutants were constructed, expressed, purified, and screened for crystallization. Only one of these six proteins yielded diffraction quality crystals. Crystals were grown of the RIIβ deletion mutant (Δ1–111) monomer potentially in complex with two cAMP molecules. X-ray diffraction quality data were obtained only after significant modification to existing purification procedures. Modifications required a Sepharose, not agarose, support for cAMP affinity chromatography followed by rapid, quantitative removal of free cAMP by size-exclusion chromatography under reducing conditions. Data to 2.4 Å resolution were collected at 29°C using synchrotron radiation on a single crystal measuring 0.2 × 0.3 × 1.2 mm³. Data were 99% complete. The hexagonal crystal belonged to space group P6₍₁₎ or P6₍₅₎ with unit cell dimensions a = b = 161.62 Å and c = 39.66 Å.     

A new structural type for a binuclear chloride-bridged copper(II) complex. Structural and magnetic characterization of di-μ-chloro-chloropentakis(benzimidazole) dicopper(II) monochloride tetrahydrate, [Cu2Cl3(C7H6N2)5]Cl·4H2O

The synthesis, crystal structure determination and magnetic properties of a new five-coordinated unsymmetrical copper(II) dinuclear complex [Cu₂Cl₃(C₇H₆N₂)₅]Cl·4H₂O are reported. The crystals are orthorhombic, space group Pnma with 4 formula units in a cell of dimensions: a = 19.506(3), b = 17.384(4), C = 11.940(2) Å. The structure was solved by direct methods. Least-squares refinement using 2138 independent reflections with I3σ(I) has led to a final value of the conventional R factor (on F) of 0.047 and R_w of 0.049. The complex cation consists of pairs of deformed trigonal-bipyramidal copper(II) centers which share an edge by two equatorial chloride ions. The equatorial coordination sites of the Cu(1) atom are occupied by three chloride ligands, while of the Cu(2) atom by two chloride and one benzimidazole ligands. The axial sites are occupied by the nitrogen atoms from four benzimidazole ligands. The Cu atoms and equatorial ligands are located on the symmetry plane. The Cu---Cu non-bonding distance in the complex is 3.386(1) Å; the two shorter bridging Cu(1)---Cl(1) and Cu(2)---Cl(1) distances are 2.402(2) and 2.424(2) Å; the two longer Cu(1)---Cl(2) and Cu(2)---Cl(2) are 2.620(2) and 2.551(2) Å. The Cu(1)---Cl(1)---Cu(2) and Cu(1)---Cl(2)---Cu(2) angles are 89.1(1) and 81.8(1)°. The structure is the first example of a bibridged binuclear complex with two non-equivalent Cu---Cl---Cu bridges. Comparison to other binuclear bis(μ-halide)-bridged copper complexes of similar structure has been made. Magnetic susceptibility measurements indicate ferromagnetic coupling of the copper(II) centers, the intramolecular exchange parameter, 2J, being 5.6 cm⁻¹ and the intermolecular one J′ = −0.6 cm⁻¹. The investigation of the electronic structure of the complex and the orbital interpretation of the magnetic coupling based on extended Hückel molecular orbital calculations are also presented.     

Molecular conformation of prostaglandin A1 monoclinic cyrstalline polymorph

The molecular conformation of the monoclinic crystalline polymorph of prostaglandin A₁ has been determined by X-ray diffraction techniques. The space group is P2₁ with a = 13.637 (2), b = 7.567 (1), I c = 10.576 (2) Å, β = 107.37 (3)°; D_c = 1.073 g·cm⁻³ for Z = 2. The molecular conformation is characterized by the nearly parallel arrangement of the C₁–C₇ and C₁₃–C₂₀ side chains, with a general flattening of the overall structure when compared with the orthorhombic polymorph. The cyclopentenone moiety assumes a C₈ envelope conformation with C₈ and O₉ displaced +0.29 Å and −0.18 Å from the C₉–C₁₀=C₁₁–C₁₂ plane respectively. Concerted, small variations of the torsion angles, primarily about the C₈–C₁₂, C₁₄–C₁₅ and C₁₆–C₁₇ bonds, bring the monoclinic and orthorhombic conformations into coincidence.     

“Action potentials” in NEUROSPORA CRASSA, a mycelial fungus

Occasional spontaneous “action potentiais” are found in mature hyphae of the fungus Neurospora crassa. They can arise either from low-level sinusoidal oscillations of the membrane potential or from a linear slow depolarization which accelerates into a rapid upstroke at a voltage 5–20 mV depolarized from the normal resting potential (near − 180 mV). The “action potentiais” are long-lasting, 1–2 min and at the peak reach a membrane potential near −40 mV. A 2− to 8−fold increase of membrane conductance accompanies the main depolarization, but a slight decrease of membrane conductance occurs during the slow depolarization. Two plausible mechanisms for the phenomenon are (a) periodic increases of membrane permeability to inorganic ions, particularly H⁺ or Cl^- and (b) periodic decreases in activity of the major electrogenic pump (H⁺) of the Neurospora membrane, coupled with a nonlinear (inverse sigmoid) current-voltage relationship.Identification of action potential-like disturbances in fungi means that such behavior has now been found in all major biologic taxa which have been probed with suitable electrodes. As yet there is no obvious function for the events in fungi.     

Anomalous carbonylation of [Pd(dppm)(O2CCF3)]2 to give an asymmetric μ-CO complex

The reactive palladium dimer, [Pd(dppm)(O₂CCF₃)]₂, is carbonylated to [Pd(dppm)(O₂CCF₃)]₂(μ-CO) in a reversible reaction with K = c. 7.2(2)x10⁴ atm⁻¹ (P_1/2 = c. 2.4 Torr). This is significantly larger than is expected based on the λ_max = 280 nm in the electronic spectrum. The product can be isolated in analytically pure form by crystallization under a CO atmosphere. It forms crystals in the monoclinic space group Cc with a = 18.584(5), b = 28.65(1), c = 11.164(3) Å and β = 95.16(2)°. The structure is significantly distorted. The bonding about the two palladium atoms is quite asymmetric. While one is close to a square planar geometry with a Pd---C(O) distance of 1.90(2) Å, the other is significantly pyramidalized and has a longer (2.00(2) Å) bond to the bridging CO. The Pd---Pd distance is only 2.896(2) Å, much shorter than that usually observed for formally non-bonded Pd atoms.     

Structure and properties of a novel OH bridged dimetal helical complex with 6,6-dimethyl-2,2′:6′,2″:6″,2:6,2-quinquepyridine ligand

A new monohelical OH⁻ bridged dinuclear complex [Zn₂(dmqpy)(OOCCH₃)₂(μ-OH)][ClO₄] · 0.5EtOH, where dmqpy is 6,6-dimethyl-2,2′:6′,2″:6″,2:6,2-quinquepyridine, has been synthesized and characterized by X-ray crystallography: monoclinic, space group P2₁/c, a=13.670(1), b=14.751(1), c=16.782(1) Å, β=96.59(1)°, U=3361.7(4) ų, Z=4, R=0.0601. Two Zn(II) ions are in different coordination modes, one is five-coordinate with a N₃O₂ donor set and the other is N₂O₂ four-coordinate with a distorted tetrahedral geometry, and the zinc ions are bridged by a hydroxyl group. The presence of the OH⁻ bridge is further confirmed by electrospray mass and infrared spectroscopies. The solution properties of the complex were investigated by ¹H NMR spectroscopy. The results of NMR indicate that the complex has higher symmetry in solution than in the solid state.     

NMR studies of glycerol permeability in lipid vesicles, erythrocytes and the alga Dunaliella

Glycerol diffusional permeabilities through the cytoplasmic cell membrane of Dunaliella salina, the cell envelope of pig erythrocyte and egg phosphattidylcholine vesicles were measured by NMR spectroscopy employing the spin-echo method and nuclear T₁ relaxation. The following permeability coefficients (P) and corresponding enthalpies of activation (ΔH^‡) were determined for glycerol at 25°C: for phosphatidylcholine vesicles 5·10⁻⁶ cm/s and 11±2 kcal/mol; for pig erythrocytes 7·10⁻⁸ cm/s and 18±3 kcal/mol, respectively; for the cytoplasmic membrane of D. salina the permeability at 17°C was found to be exceptionally low and only a lower limit (P<5·10⁻¹¹cm/s) could be calculated. At temperatures above 50°C a change in membrane permeability occurred leading to rapid leakage of glycerol accompanied by cell death. The data reinforce the notion that the cytoplasmic membrane of Dunaliella represents a genuine anomaly in its exceptional low permeability to glycerol.     

Identification and characterization of beta1-adrenergic receptors in rat parotid membranes

&#x02022; Beta-adrenergic receptor identification and properties are probed in rat parotid membranes utilizing the high affinity β-adrenergic antagonist(−)-[³H]dihydroalprenolol.

&#x02022; The binding of (−)-[³H]dihydroalprenolol to membrane preparations of parotid is rapid, equilibrium being reached in 5 min. Strict stereospecificity is observed, (−)-propanolol being 100 times more potent than (+)-propranolol in competing with (−)-[³H]dihydroalprenolol for binding sites. Beta-adrenergic agonists compete for the binding sites with (−)-[³H]dihydroalprenolol with the same characteristics, i.e., much higher concentrations of the (+)-stereoisomers than the (−)-stereoisomers are required to produce 50% inhibition, the range varies from 14-fold for epinephrine to 300-fold for isoproterenol. Among the (−)-stereoisomers, the relative potency of inhibitory action is (−)-propranolol > (−)-isoproterenol > (−)-epinephrine ≡ (−)-norepinephrine. (−)-Isoproterenol is about 20 times as potent as norepinephrine, the least potent agonist among all the catecholamine (−)-stereoisomers.

&#x02022; The binding of (−)-[³H]dihydroalprenolol is saturable, with a maximum number of binding sites equalling 450 fmol/mg protein and a dissociation constant of 7.9 nM. The Scatchard plots show no significant curvilinear character. Hill plots consistently give a Hill coefficient close to unity (0.92–1.05). Both pieces of evidence suggest a single-component system with no significant cooperativity.

&#x02022; Dissociation kinetics study after the method of De Metys et al. (1973) Biochem. Biophys. Res. Commun. 155, 154, indicates a lack of site-to-site interactions among the binding sites. The rate of dissociation of bound (−)-[³H]dihydroalprenolol is the same in the presence and absence of 1 · 10⁻⁵ M (±)-alprenolol.

&#x02022; Based on the binding of (−)-[³H]dihydroalprenolol, it is concluded that the beta-adrenergic receptors can be identified in rat parotid and that these binding sites display β₁ character. Results of the study indicate a one-component system with no observable site-to-site interactions.

Characteristics of fed-batch cultures of recombinant <Emphasis Type="Italic">Escherichia coli</Emphasis> containing human-like collagen cDNA at different specific growth rates

Fed-batch cultures of recombinant Escherichia coli BL21 for producing human-like collagen were performed at different specific growth rates (0.1~0.25 h⁻¹) before induction and at a constant value of 0.05 h⁻¹ after induction by the method of pseudo-exponential feeding. Although the final biomass (around 69 g l⁻¹) was almost the same in all fed-batch cultures, the highest product concentration (13.6 g l⁻¹) was achieved at the specific growth rate of 0.15 h⁻¹ and the lowest (9.6 g l⁻¹) at 0.25 h⁻¹. The mean productivity of human-like collagen was the highest at 0.15 h⁻¹ (0.57 g l⁻¹ h⁻¹) and the lowest at 0.1 h⁻¹ (0.35 g l⁻¹ h⁻¹). In the phase before induction, the cell yield coefficient (Y_X/S) decreased when the specific growth rate increased, while the formation of acetic acid increased upto 2.5 g l⁻¹ at 0.25 h⁻¹. The mean product yield coefficient (Y_P/S) also decreased with specific growth rate increasing. The respiration quotient (RQ) increased slightly with specific growth rate increasing before induction, and the mean value of RQ was around 72%. The optimum growth rate for human-like collagen production was 0.15~0.2 h⁻¹.