Effects of temperature and field strength on the NMR relaxation times of Na in frog striated muscle

Pulsed NMR techniques have been applied to the study of the relaxation parameters characterizing ²³Na within frog striated muscle. Experiments were performed at 3°C, 22–24°C and 39°C at a Larmor frequency of 15.7 MHz; at 22–24°C, measurements were obtained both at 15.7 MHz and at 7.85 MHz.As previously reported, only a single spine-lattice relaxation time (T₁) was observed, but both slow (T₂)_I and fast (T₂)_II components of the spin-spin relaxation time were measured. The effect of temperature (θ) upon (1/T₁) was qualitatively similar to that reported for ²³Na in free solution; (θ) did not significantly affect (1/T₂) over the range of temperatures studied. (1/T₂)_I, and to a lesser degreee, (1/T₁) exhibited a modest inverse dependence of doubtful significance on the Larmor frequency.The data are examined within the framework of a simple specific model; a conservative values in assumed for the quadrupolar coupling constant characterizing immobilized intracellular Na⁺. Within this framework, the results suggest that the fraction of bound ions whose molecular tumbling is severely restricted does not exceed some few percent of the total sodium population.     

Structural modifications and thermal transitions of standard maize starch after DIC hydrothermal treatment

Standard maize starch was hydrothermally treated by Instantaneous Controlled Pressure Drop (DIC) process at three pressure levels (1, 2 and 3 bar) corresponding to the temperatures of 100, 122 and 135 °C (at 13–27% moisture), respectively. The structural effects of various hydrothermal conditions were examined with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. In order to understand the changes that occur during DIC treatment, melting endotherms of native maize starch at various moisture contents were determined. The gelatinization temperatures of DIC treated standard maize starch increased with DIC treatment. The transition temperatures (T_o, T_p) are closely related to the combined effect of pressure and processing time. At approximately 10 min of processing time, T_o and T_p were 65.7 and 72.3, 68.8 and 73.6 °C, 74.8 and 79.8 °C for pressure levels of 1, 2 and 3 bar, respectively (against 63.1 and 69.6 °C for native starch). DIC treatment narrowed the gelatinization temperature range and decreased gelatinization enthalpy (ΔH), as the severity of processing conditions increased. ΔH decreased from 11.4 J g⁻¹ (native) to 11.0 (1 bar), 9.0 (2 bar) and 1.7 J g⁻¹ (3 bar) for treated maize starch during approximately 10 min. Relative crystallinity of hydrothermally treated starch decreased with increasing DIC conditions. The A-type crystalline pattern was progressively lost (at pressure level 2 bar) and substituted by the V_h-type X-ray diffraction pattern, corresponding to the formation of amylose–lipid complexes. For severe DIC conditions (pressure level of 3 bar), the substitution was completed. Microscopic observations revealed progressive loss of the birefringence of DIC treated starch granules except at low pressure (1 bar), while the integrity of starch granules was preserved for all the conditions. These modifications that reveal important changes in the crystalline organization of the starch granules are related to their functional properties.     

Metabolic rate, maximum metabolism, and advantages of torpor in the fat mouse Steatomys pratensis natalensis Roberts, 1921 (Dendeomurinae)

1. The fat mouse Steatomys pratensis natalensis (mean body mass 37.4±0.43 (se)) has a low euthermic body temperature T_b=30.1–33.8 °C and a low basal metabolic rate (BMR)=0.50 ml O₂ g⁻¹ h⁻¹.

2. Below an ambient temperature (T_a)=15 °C, the mice were hypothermic.

3. The lowest survivable T_a=10 °C.

4. Torpor is efficient in conserving energy between T_a=15–30 °C, below T_a=15 °C, the mice arouse.

5. Euthermic and torpid mice were hyperthermic at T_a=35 °C.

6. Thermal conductance was 0.159 ml O₂ g⁻¹ h⁻¹ °C⁻¹, 98.8% of the expected value.

7. Non-shivering thermogenesis (NST) was 2.196 ml O² g⁻¹ h⁻¹ (3.69×BMR).

8. Maximal oxygen consumption, however, was 3.83 ml O₂ g⁻¹ h⁻¹ (6.44×BMR), indicating that other methods of heat production are additive.

9. Because fat mice conserve energy by torpor only between T_a=15–30 °C, we suggest that torpor may be a more important mechanism for surviving food shortages than for surviving cold weather.

Using species-specific paleotemperature equations with foraminifera: a case study in the Southern California Bight

Species-specific paleotemperature equations were used to reconstruct a record of temperature from foraminiferal δ¹⁸O values over the last 25 kyr in the Southern California Bight. The equations yield similar temperatures for the δ¹⁸O values of Globigerina bulloides and Neogloboquadrina pachyderma. In contrast, applying a single paleotemperature equation to G. bulloides and N. pachyderma δ¹⁸O yields different temperatures, which has been used to suggest that these species record the surface-to-thermocline temperature gradient. In Santa Barbara Basin, an isotopically distinct morphotype of G. bulloides dominates during glacial intervals and yields temperatures that appear too cold when using a paleotemperature equation calibrated for the morphotype common today. When a more appropriate paleotemperature equation is used for glacial G. bulloides, we obtain more realistic glacial temperatures. Glacial–interglacial temperature differences (G–I ΔT) calculated in the present study indicate significant cooling (8–10°C) throughout the Southern California Bight during the last glacial maximum (LGM). The magnitude of glacial cooling varies from 8°C near the middle of the Southern California Bight (Tanner Basin and San Nicolas Basin) to 9°C in the north (Santa Barbara Basin) and 9.5–10°C in the south (Velero Basin and No Name Basin). Our temperature calculations agree well with previous estimates based on the modern analog technique. In contrast, studies using N. pachyderma coiling ratios, U^k′₃₇ indices, and transfer functions estimate considerably warmer LGM temperatures and smaller G–I ΔT.     

Pressure dependence of the apparent specific volume of bovine serum albumin: Insight into the difference between isothermal and adiabatic compressibilities

There are some theoretical arguments related to interpreting the adiabatic compressibility (β_s) of a protein determined from the sound velocity and the difference between β_s and isothermal compressibility (β_T). To address these problems experimentally, we constructed a high-pressure oscillating densitometer and used it to measure the apparent specific volume of bovine serum albumin as a function of pressure (0.1–78 MPa) and temperature (5–35 °C). The β_T determined from plots of the apparent specific volume vs. pressure was slightly larger than β_s at all temperatures examined, with the difference between the two compressibilities increasing as the temperature was decreased. Only at room temperature did the observed β_T agree with those estimated from β_s using the heat capacity and the thermal expansibility of the protein, suggesting that there are significant as-yet-unknown mechanisms that affect protein compressibility.     

Diversity in amylopectin structure, thermal and pasting properties of starches from wheat varieties/lines

Structural, thermal and pasting diversity of starches from Indian and exotic lines of wheat was studied. Majority of the starches showed amylose content ranging between 22% and 28%. Endotherm temperatures (T_o, T_p and T_c) of the starches showed a range between 56–57, 60 –61 and 65.5–66.5 °C, respectively. Exotherms with T_p between 87.0 and 88.2 °C were observed during cooling of heated starches, indicating the presence of amylose–lipid complexes. Exotherm temperatures were negatively correlated to swelling power. Amylopectin unit chains with different degree of polymerization (DP) were observed to be associated with pasting temperature, setback and thermal (endothermic T_o, T_p, and T_c) parameters. Amylopectin unit chains of DP 13–24 showed positive relationship with endothermic T_o, T_p and T_c. Pasting temperature showed positive correlation with short chains (DP 6–12) while negative correlation with medium chain (DP 13–24) amylopectins. Setback was positively correlated to DP 16–18 and negatively to DSC amylose–lipid parameters.     

Thermoregulation of water foraging wasps (Vespula vulgaris and Polistes dominulus)

A comparison of the thermoregulation of water foraging wasps (Vespula vulgaris, Polistes dominulus) under special consideration of ambient temperature and solar radiation was conducted. The body surface temperature of living and dead wasps was measured by infrared thermography under natural conditions in their environment without disturbing the insects’ behaviour. The body temperature of both of them was positively correlated with T_a and solar radiation. At moderate T_a (22–28 °C) the regression lines revealed mean thorax temperatures (T_th) of 35.5–37.5 °C in Vespula, and of 28.6–33.7 °C in Polistes. At high T_a (30–39 °C) T_th was 37.2–40.6 °C in Vespula and 37.0–40.8 °C in Polistes. The thorax temperature excess (T_th–T_a) increased at moderate T_a by 1.9 °C (Vespula) and 4.4 °C (Polistes) per kW⁻¹ m⁻². At high T_a it increased by 4.0 °C per kW⁻¹ m⁻² in both wasps. A comparison of the living water foraging Vespula and Polistes with dead wasps revealed a great difference in their thermoregulatory behaviour. At moderate T_a (22–28 °C) Vespula exhibited distinct endothermy in contrast to Polistes, which showed only a weak endothermic activity. At high T_a (30–39 °C) Vespula reduced their active heat production, and Polistes were always ectothermic. Both species exhibited an increasing cooling effort with increasing insolation and ambient temperature.     

T-wave width as an index for quantification of ventricular repolarization dispersion: Evaluation in an isolated rabbit heart model

This study examined the significance of ECG-derived indexes in quantifying ventricular repolarization dispersion (VRD) given its value as a risk marker for severe myocardial arrhythmia. Multilead ECG recordings from an isolated rabbit heart model, including control and globally increased VRD (IVRD) beats, were studied. The IVRD was induced by supplying d-Sotalol (DS) or premature ventricular stimulation (PVS). ECG indexes came from (a) the absolute ECG summation signal, from which we obtained the amplitude and area of the T-wave, and the T-wave width (T_W), which we consider as IVRD indexes, and (b) the Singular Value Decomposition (SVD) of the ECG, from which the θ_PT (angle between the first SVD principal axis and the repolarization axis), T-wave residuum (T_WR), T-wave morphology dispersion (T_MD), unnormalized T_MD (UT_MD), and θ_RT (the angle between the depolarization and the repolarization vectors) were estimated as IVRD indexes. Results were compared with the classical QT-based VRD indexes (σ_QTe, standard deviation of QT end). The main results are T_W: 78.0±10.3 vs. 133.6±29.6 ms, for control vs. IVRD generated using DS, p<0.005 and 95.2±7.9 vs. 118.5±15.7 ms when PVS was used, p<0.007; σ_QTe: gives 6.5±1.4 vs. 11.6±1.9 ms, for DS p<0.007 and 7.6±2.2 vs. 13.0±3.4 ms for PVS, p<0.007; respectively. θ_PT: 35±51° vs. 117±49°, p<0.009 in DS. We concluded that globally induced IVRD is well reflected by the T_W parameter, being the most sensitive of the studied ones. The IVRD can also be quantified by using the θ_PT index.     

Biosynthesis of medium chain length poly(3-hydroxyalkanoates) (mcl PHAs) from cosmetic co-products by Pseudomonas raguenesii sp. nov., isolated from Tetiaroa, French Polynesia

A new bacterium, designated as strain TE9 was isolated from a microbial mat in French Polynesia and was studied for its ability to synthesize medium chain length poly-β-hydroxyalkanoates (mcl PHAs) during cultivation on cosmetics co-products. The composition of PHAs was analysed by coupled gas chromatography mass spectroscopy (GC/MS), nuclear magnetic resonance (NMR) and Fourier Transform InfraRed (FTIR) spectroscopy. PHAs were composed of C6–C14 3-hydroxyacids monomers, with a predominance of 3-hydroxyoctanoate (3HO), 3-hydroxydecanoate (3HD) and 3-hydroxydodecanoate (3HDD). Differential scanning calorimetry (DSC) experiments allowed the characterization of elastomeric materials with a melting point T_m near 50 °C, enthalpy of fusion ΔH_m from 27 to 32 J/g, and glass transition temperature T_g of −43 °C. Molecular weights ranged from 175,000 to 358,000 g/mol. On the basis of the phenotypical features and genotypic investigations, strain TE9 was assigned to the Pseudomonas genus and the name of Pseudomonas raguenesii sp. nov. is proposed.     

A structural transition in egg lecithin-cholesterol bilayers at 12 °C

The thermal coefficient of expansion of egg lecithin bilayer thickness, αd₁, was measured as a function of its cholesterol content up to mole ratio lecithin/cholesterol of 1:1, and over the temperature range 0–40 °C. At all cholesterol contents αd₁ changes abruptly at approximately 12 °C indicating a structural transition at this temperature. Above 12 °C, αd₁ decreases monotonically from −2·10⁻³ for pure egg lecithin to −1·10^–3 at mole ratio 1:1. Below 12 °C αd₁ is walways higher than above 12 °C and shows a sharp, anomalously high value of −6·10⁻³ at the mole ratio 2:1. The results have been interpreted as the movement of cholesterol into the bilayer or the formation of lecithin-cholesterol “complexes” at temperatures below 12 °C. Similar studies with phosphatidylinositol containing cholesterol showed no structural transition and lysolecithin containing cholesterol behaved differently giving two lamellar phases in equilibrium.     

Synthesis and characterization of homochiral polymeric S-malato molybdate(VI): toward the potentially stereospecific formation and absolute configuration of iron-molybdenum cofactor in nitrogenase

Reaction of sodium or potassium molybdate and excess malic acid in a wide range of pH values (pH 4.0–7.0) resulted in the isolation of two cis-dioxo-bis(malato)-Mo(VI) complexes, viz. Na₃[MoO₂H(S-mal)₂] and K₃[MoO₂H(S-mal)₂]·H₂O (H₃mal=malic acid). The sodium complex is also characterized by an X-ray structure analysis, showing that the mononuclear Mo units are linked together via very strong symmetric CO₂···H··· O₂C-hydrogen bond [2.432(5) Å], forming a polymeric chain. The molybdenum atoms are quasi-octahedrally coordinated by two cis-oxo groups and two bidentate malate ligands via its alkoxy and α-carboxyl groups, while the β-carboxylic and carboxylate groups remain uncomplexed, as the coordination of vicinal carboxylate and alkoxide of homocitrate in FeMo cofactor of nitrogenase. The absolute configuration of the metal center in this S-malato complex is assigned as Λ and the homochirality within the chain is established as a homochiral form ···Λ_S–Λ_S–Λ_S–Λ_S···. It is proposed that the chiral configuration of the metal center in wild-type FeMo-co biosynthesis might be induced by the early coordination of the chiral R-homocitric acid, while a mixture of raceme might be obtained in the biosynthesis of NifV⁻ FeMo-cofactor. The absolute configuration of wild-type FeMo-cofactor is assigned as Δ_R.     

Study of water permeability through phospholipid vesicle membranes by O NMR

Vesicle suspensions of up to 5 % egg lecithin and 2.5 % cholesterol have been found to have no effect on the NMR relaxation times of ¹⁷O from water. Addition of 1–5 mM Mn²⁺ to an equimolar vesicle suspension of egg lecithin and cholesterol permitted resolution of the free induction decay into two exponential components, a fast one arising from the external water and a slow one arising from the intravesicular fluid. From the rates of relaxation the mean life time of the water molecules within the vesicles was calculated to be 1±0.1 ms at 22°C. The size of the vesicle was estimated from electron micrographs to be about 500 Å in diameter. These data yield an equilibrium water permeability, P_w, of about 8 μs⁻¹ for the vesicle membranes. From the temperature dependence of P_w an activation energy of 12±2 kcal/mol was obtained. The longitudinal relaxation time (T₁) of water within vesicles remained the same as in pure water.     

TPA Increases Conductance but Decreases Permeability in Neonatal Rat Cardiomyocyte Gap Junction Channels

Short-term (10 min) effects of 100 nM 12-O-tetradecanoylphorbol-13-acetate (TPA), the protein kinase C (PKC) activator, on cardiac macroscopic (g_j) and single channel (γ_j) gap junctional conductances were studied in pairs of neonatal rat cardiomyocytes. Under dual whole-cell (WC) or perforated patch (PP) voltageclamp, g_j increased by 15.5 ± 7.2% (mean ± SD, n = 9) and by 46.3 ± 17.0% (n = 5), respectively. The latter difference is not related to intracellular calcium concentration, because raising the Ca²⁺ concentration in the electrode solution did not change the TPA-induced increase in g_j observed under WC conditions. The inactive phorbol ester, 4α-phorbol 12,13-didecanoate (αPDD), did not affect g_j. Single cardiac gap junction channel events, resolved in the presence of heptanol, indicated two γ_j sizes of 20 and 40-45 pS. Under control conditions, the larger events were most frequently observed. Whereas αPDD did not change this distribution, TPA shifted the γ_j distribution to the lower sizes. Diffusion of Lucifer Yellow (LY) and 6-carboxyfluorescein (6-CF), gap junction permeant tracers, was studied on small clusters of cardiomyocytes. Under control conditions, LY labeled 19.4 ± 7.2 cells (mean ± SD, n = 18) and 6-CF labeled 8.4 ± 2.2 cells (n = 20). Whereas αPDD did not change the extent of dye transfer, TPA restricted the diffusion of LY to 2.8 ± 1.3 cells (n = 11) and of 6-CF to 2.4 ± 1.4 cells (n = 20). This suggests that permeability and single channel conductance of connexin 43 channels are parallely related. Altogether, these results point to the opposite modulation of electrical and metabolic coupling of cardiac cells evoked by TPA.     

Water in normal muscle and muscle with a tumor

The total water content, the amount of non-freezable water, and the Na⁺ and K⁺ contents in the gastrocnemius muscle of albino mice with and without a solid tumor were determined. The spin-lattice relaxation time (T₁) for the water protons in the two kinds of muscle were measured at six resonance frequencies ranging from 4.5 to 60 MHz over the temperature range +37 to −65°C. Quantitatively calculated T₁ values are given. The difference in T₁ for the two types of muscle at temperatures above −5°C is attributed to the difference in the distribution ratio of water between hydration and free states, and bears no direct relation to the concentration of Na⁺.     

Freeze or dehydrate: only two options for the survival of subzero temperatures in the arctic enchytraeid<Emphasis Type="Italic"> Fridericia ratzeli</Emphasis>

Hygrophilic soil animals, like enchytraeids, overwintering in frozen soil are unlikely to base their cold tolerance on supercooling of body fluids. It seems more likely that they will either freeze due to inoculative freezing, or dehydrate and adjust their body fluid melting point to ambient temperature as has been shown for earthworm cocoons and Collembola. In the present study we tested this hypothesis by exposing field-collected adult Fridericia ratzeli from Disko, West Greenland, to freezing temperatures under various moisture regimes. When cooled at –1 °C min^–1 under dry conditions F. ratzeli had a mean temperature of crystallisation (T_c) of –5.8 °C. However, when exposed to temperatures above standard T_c for 22 h, at –4 °C, most individuals (90%, n= 30) remained unfrozen. Slow cooling from –1 °C to –6 °C in vials where the air was in equilibrium with the vapour pressure of ice resulted in freezing in about 65% of the individuals. These individuals maintained a normal body water content of 2.7–3.0 mg mg^–1 dry weight and had body fluid melting points of about –0.5 °C with little or no change due to freezing. About 35% of the individuals dehydrated drastically to below 1.1 mg mg^–1 dry weight at –6 °C, and consequently had lowered their body fluid melting point to ca. –6 °C at this time. Survival was high in both frozen and dehydrated animals at –6 °C, about 60%. Approximately 25% of the animals (both frozen and dehydrated individuals) had elevated glucose concentrations, but the mean glucose concentration was not increased to any great extent in any group due to cold exposure. The desiccating potential of ice was simulated using aqueous NaCl solutions at 0 °C. Water loss and survival in this experiment were in good agreement with results from freezing experiments. The influence of soil moisture on survival and tendency to dehydrate was also evaluated. However, soil moisture ranging between 0.74 g g^–1 and 1.15 g g^–1 dry soil did not result in any significant differences in survival or frequency of dehydrated animals even though the apparent wetness and structure of the soil was clearly different in these moisture contents.Abbreviations DW dry weight - FW fresh weight - MP melting point - RH relative humidity - Tc crystallisation temperatures - WC water contentCommunicated by I.D. Hume     

Evidence of α fluctuations in myoglobin's denaturation in the high temperature region: Average relaxation time from an Adam–Gibbs perspective

In this work, we derive an analytical expression for the relaxation time τ as a function of temperature T for myoglobin protein (Mb, PDB:1MBN) in the high temperature limit (T > T_g = 200 K). The method is based on a modified version of the Adam–Gibbs theory (AG theory) for the glass transition in supercooled liquids and an implementation of differential geometry techniques. This modified version of the AG theory takes into account that the entropic component in protein's denaturation has two major sources: a configurational contribution ΔS_c due to the unfolding of the highly ordered native state N and a hydration contribution ΔS^hyd arising from the exposure of non-polar residues to direct contact with solvent polar molecules. Our results show that the configurational contribution ΔS_c is temperature-independent and one order of magnitude smaller than its hydration counterpart ΔS^hyd in the temperature range considered. The profile obtained for log τ(T) from T = 200 K to T = 300 K exhibits a non-Arrhenius behavior characteristic of α relaxation mechanisms in hydrated proteins and glassy systems. This result is in agreement with recent dielectric spectroscopy data obtained for hydrated myoglobin, where at least two fast relaxation processes in the high temperature limit have been observed. The connection between the relaxation process calculated here and the experimental results is outlined.     

Reproductive and developmental biology of Gonatocerus ashmeadi (Hymenoptera: Mymaridae), an egg parasitoid of Homalodisca coagulata (Hemiptera: Cicadellidae)

The reproductive and developmental biology of Gonatocerus ashmeadi Girault, a parasitoid of the glassy-winged sharpshooter Homalodisca coagulata (Say), was determined at five constant temperatures in the laboratory: 15; 20; 25; 30; 33 °C. At 30 °C, G. ashmeadi maintained the highest successful parasitism rates with 46.1% of parasitoid larvae surviving to adulthood. Lifetime fecundity was greatest at 25 °C and fell sharply as temperature either increased or decreased around 25 °C. Temperature had no effect on sex ratio of parasitoid offspring. Mean adult longevity was inversely related to temperature with a maximum of 20 days at 15 °C to a minimum of eight days at 33 °C. Developmental rates increased nonlinearly with increasing temperatures. Developmental rate data were fitted with the modified Logan model for oviposition to adult development times across each of the five experimental temperatures to determine optimal and upper lethal temperature thresholds. The lower developmental threshold estimated by the Logan model and linear regression were 1.10 and 7.16 °C, respectively. Linear regression of developmental rate for temperatures 15–30 °C indicated that 222 degree-days were required above a minimum threshold of 7.16 °C to complete development. A temperature of 37.6 °C was determined to be the upper development threshold with optimal development occurring at 30.5 °C. Demographic parameters were calculated and pseudo-replicates for intrinsic rate of increase (r_m), net reproductive rates (R_o), generation time (T_c), population doubling time (T_d), and finite rate of increase (λ) were generated using the bootstrap method. Mean bootstrap estimates of demographic parameters were compared across temperatures using ANOVA and nonlinear regression.     

Anti-plasticization of cassava starch by complexing fatty acids

The effect of adding 1–8% amylose complexing fatty acids (CFA), such as linoleic and oleic acids, on the glass transition temperature (T_g) of cassava starch (CS) with moisture content varying from 5 to 35% (dry basis) was studied. The main relaxation temperature (T_α), associated with the glass transition temperature of the samples (T_g), was determined by dynamic-mechanical-thermal analysis. The plasticizing behavior of water in the blends was evidenced by a decrease of T_α values with moisture content. The effect of CFA on CS was found to be a function of moisture content. At low moisture (<11%) it caused an anti-plasticization effect, while at higher moisture contents it produced plasticization. The anti-plasticizing effect of CFA on CS was attributed to amylose–lipid complex formation.     

Purification and properties of a novel raw starch degrading-cyclodextrin glycosyltransferase from Klebsiella pneumoniae AS- 22

A novel raw starch degrading α-cyclodextrin glycosyltransferase (CGTase; E.C. 2.4.1.19), produced by Klebsiella pneumoniae AS-22, was purified to homogeneity by ultrafiltration, affinity and gel filtration chromatography. The specific cyclization activity of the pure enzyme preparation was 523 U/mg of protein. No hydrolysis activity was detected when soluble starch was used as the substrate. The molecular weight of the pure protein was estimated to be 75 kDa with SDS-PAGE and gel filtration. The isoelectric point of the pure enzyme was 7.3. The enzyme was most active in the pH range 5.5–9.0 whereas it was most stable in the pH range 6–9. The CGTase was most active in the temperature range 35–50°C. This CGTase is inherently temperature labile and rapidly loses activity above 30°C. However, presence of soluble starch and calcium chloride improved the temperature stability of the enzyme up to 40°C. In presence of 30% (v/v) glycerol, this enzyme was almost 100% stable at 30°C for a month. The K_m and k_cat values for the pure enzyme were 1.35 mg ml⁻¹ and 249 μM mg⁻¹ min⁻¹, respectively, with soluble starch as the substrate. The enzyme predominantly produced α-cyclodextrin without addition of any complexing agents. The conditions employed for maximum α-cyclodextrin production were 100 g l⁻¹ gelatinized soluble starch or 125 g l⁻¹ raw wheat starch at an enzyme concentration of 10 U g⁻¹ of starch. The α:β:γ-cyclodextrins were produced in the ratios of 81:12:7 and 89:9:2 from gelatinized soluble starch and raw wheat starch, respectively.     

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.