Specificity of the cholesterol side-chain cleavage enzyme system of adrenal cortex

Incubation of lanosta-8, 24-dien-3β-o1-1,2- ³H and lanost-8-en-3β-o1-1, 2-³H with an adrenocortical bovine mitochondrial acetone-dried preparation did not yield any significant ( < 0.01%) 3β-hydroxy-4, 4, 14-trimethyl-5α-pregn-8-en-20-one. Under the same conditions cholesterol-1,2-³H yielded 8.3% pregnenolone. Incubation of (20S?) — 17α, 20-dihydroxycholesterol-7-³ H yielded 0.6 to 1.6% (20SS?, 22R?) — 17α, 20, 22-trihydroxycholesterol, 1.0 to 3.2% of 17α-hydroxypregnenolone, but no significant ( < 0.02%) (20S, 22S)-17α, 20, 22-trihydroxycholesterol. In another experiment incubation of cholesterol-1, 2-³H yielded 5% pregnenolone, 0.5% 17α-hydroxypregnenolone, 0.2% (20R?,22R?)-20, 22-dihydroxy-cholesterol, but no significant ( < 0.01%) 17α-hydroxy-cholesterol, (20S?) -17α, 20-dihydroxycholesterol or (20S?, 22R?)-17α, 20, 22-trihydroxycholesterol.     

Lake Chapo: a baseline study of a deep, oligotrophic North Patagonian lake prior to its use for hydroelectricity generation: I. Physical and chemical properties

A baseline study on a temperate, oligotrophic North Patagonian lake (Lake Chapo, Southern Chile) was made prior to the installation of a hydroelectric power station. Throughout one year (September 1986–October 1987) the physical and chemical properties of the lake were investigated monthly from the surface to a depth of 40 m. Lake Chapo is a deep, transparent (Secchi depth: 17–25 m), glacial lake located at 41°?27.5′?S and 72°?30′?W. It has a maximum depth of 298 m, mean depth of 183 m, surface area of 45.3 km² and water volume of 8.296 km³. The theoretical residence time of the water was 5.5 years. The temperature regime is monomictic with the mixed temperature between 8.1–8.8?°C. Maximum temperature at the surface was 18.7?°C during thermal stratification in summer when the epilimnion had a thickness of about 20 m. The conductivity was low (20.3–23.8 μS cm^?1) as was the buffering capacity of a predominantly CO₂-carbonate system. The predominant cations were Ca⁺²¿ Na⁺¿Mg⁺²¿K⁺. The phosphorous and nitrogen contents were very low (soluble reactive ortophosphate: 0–1.5 μg P l^?1, total phosphorus: 0.3–4 μg P l^?1 and nitrate: 0–35 μg N l^?1), which is typical of North Patagonian lakes.     

Properties of antisera to progesterone and to 17-hydroxy-progesterone elicited by immunization with the steroids attached to protein through position 7

Antibodies to progesterone (P) and to 17-hydroxyprogesterone (17-OHP) were raised by immunization of rabbits with progesterone-7α-carboxyethyl thioether--bovine serum albumin (P-7—BSA) or with 17-OHP-7α-carboxyethyl thioether--BSA (17-OHP-7--BSA). The antisera produced were of high affinity: K_a towards the homologous hapten was 3. 7 × 10¹⁰ 1./mol for the anti-P serum and 5. 9 × 10⁹ 1/mol for the anti-17-OHP serum. The antiserum to P-7—BSA displayed little or no cross reaction (?= 2%) with the 20α-, 20β- or 5β-dihydro-derivatives of progesterone, moderate cross-reaction with pregnenolone (4%), but considerable cross-reaction with 11-deoxycorticosterone (7%), 5α-dihydro-progesterone (11%) and 17-OHP (15%). The antiserum to 17-OHP-7--BSA showed very little cross-reaction (?= 2%) with progesterone and other steroids lacking a 17α-hydroxyl group, such as pregnenolone or 11-deoxycorticosterone, but reacted significantly with 17α, 21-dihydroxy-4-pregnene-3, 20-dione (8%) and 3β, 17-dihydroxy-5-pregnen-20-one (13%). None of the sera reacted with testosterone, cortisol or estradiol-17β. It appears that conjugation of progesterone to protein through carbon-7 affords antisera comparable in specificity to those raised with 11α-conjugates and superior to those raised with 3-, 6- and 20-conjugates. The antiserum to 17-hydroxyprogesterone described is the first one that specifically recognizes this metabolite.     

Metabolism of estrone sulfate in the pregnant sheep

The metabolism of ³H-estrone sulfate (³H-E₁S) in 4 pregnant sheep, two injected i.v. and two i.m., has been studied. Intravenously injected ³H-E₁S had a plasma half-life of approximately 8 min, and metabolic clearance rate of approximately 800 ml/min. Using this clearance rate and the previously published mean plasma concentration of E₁S, the estimated production rate of E₁S is between 8.8 nmol (3.3 μg) and 78.2 nmol (29.1 μg) per min from 2-day to 0-day before parturition.Intramuscularly injected ³H-E₁S disappeared from plasma linearly and was completely cleared well within 3 hours. In all cases, whether i.v. or i.m. injected, the main metabolite isolated was ³H-estradiol-17β-3-sulfate, with only a trace amount as ³H-estradiol-17β-3-sulfate.     

Further survey of chromosomal polymorphisms in the freshwater planarian Polycelis auriculata

Although the chromosomal number of Polycelis (Seidlia) auriculata Ijima et Kaburaki is basically 2n = 6, this species shows remarkable chromosomal polymorphisms in different populations. Among worms collected at 30 stations in the central part of Japan's Main Island and in Hokkaido, we found five new karyotypes, considered to be variations of tetraploidy and diploidy: 4n?fis¹. + 1 = 3SM + 2A + 3T₁ + 2T₂ + 4M = 14, 4n?fis².(B) = 2SM + 2A + 4T₁ + 2T₂ + 4M + (0?2B) = 14 –16, 4n?fis². + 1 = 2SM + 2A + 4T₁ + 2T₂+5M= 15, 4n?fis².?2 = 2SM + 2A + 4T₁ + 4M = 12, and 2nM- = 2SM + 2A = 4 (where SM = submetacentric; A = acrocentric; T₁ and T₂ = telocentric; M = metacentric; B = B-chromosome; fis¹. and fis². = occurrence of one or two centric fissions, respectively; and M- = deletion of a metacentric chromosome). These karyotypes exist singly in one individual or as various mixoploids within the same individual. No individual having only karyotype 2nM- has yet been found. This brings the total number of known karyotypes in P. auriculata to 17; these can be arranged in an order that we believe reflects their evolution.     

Design and synthesis of pyrazolopyridine derivatives as sphingosine 1-phosphate receptor 2 ligands

Eleven new sphingosine 1-phosphate receptor 2 (S1PR2) ligands were synthesized by modifying lead compound N-(2,6-dichloropyridin-4-yl)-2-(4-isopropyl-1,3-dimethyl-1H-pyrazolo[3,4-b]pyridin-6-yl)hydrazine-1-carboxamide (JTE-013) and their binding affinities toward S1PRs were determined in vitro using [³²P]S1P and cell membranes expressing recombinant human S1PRs. Among these ligands, 35a (IC₅₀?=?29.1?±?2.6?nM) and 35b (IC₅₀?=?56.5?±?4.0?nM) exhibit binding potency toward S1PR2 comparable to JTE-013 (IC₅₀?=?58.4?±?7.4?nM) with good selectivity for S1PR2 over the other S1PRs (IC₅₀?>?1000?nM). Further optimization of these analogues may identify additional and more potent and selective compounds targeting S1PR2.     

Mechanism of the interaction of aliphatic alcohols with bovine serum albumin in the ternary systems—1H n.m.r. study: 2. Aqueous solutions BSA-alcohols-sulphonamides

To study effect of sulphacetamide and sulphathiazole on the interaction of aliphatic alcohols with bovine serum albumin (BSA) in aqueous solution, ¹H n.m.r. spectra of alcohols (A) and sulphonamides (S) were monitored in D₂O, in the binary systems (A—S), (A—BSA), (S—BSA) and in the ternary system (A—BSA—S) at pH 7.0. The n.m.r. lines of alcohols, markedly and selectively broadened in the systems (A—BSA), were gradually narrowed on addition of increasing concentrations of sulphonamides. The narrowing was dependent on the chain length and branching of the alcohol molecules with residual broadening significantly greater for the α-methylenes or methines next to ?OH. The results suggest the release of alcohol molecules weakly associated to BSA after the formation of the specific sulphonamide—BSA complex. They also reflect selectively strong immobilization of the fragments next to ?OH in the A—BSA complexes, probably by hydrogen bonds between hydroxyls and the peptide groups of protein.     

Characterization of phosphate absorption in maize root cortex segments

Uptake of phosphate ions by 1 mm segments of isolated maize root cortex layers was studied. Cortex segments (from roots of 8 days old maize plants) absorb phosphate ions from 1 mM KH₂PO₄ in 0.2 mM CaSCO₄ at the average rate of 34.3 ±3.2 μg P_i g^?1 (fr. m.) h^?1,i.e. 0.35± 0.02 μmol P_i g^?1 (fr. m.) h^?1. Phosphate uptake considerably increases after a certain period of “augmentation”,i.e. washing in aerated 0.2 mM CaSO₄. This increase is completely blocked by the presence of 10 μg ml^?1 cycloheximide. The relation of uptake rate to phosphate concentration in the medium was shown to have 3 phases in the concentration range of 0.02 - 40 mM. Transition points were found between 0.8–1 mM and 10–20 mM. Following K_m and V_max values were found: K_m[mM] : 0.37 - 3.82 - 27.67 V_max[μg P_i g^?1 (fr. m.) h^?1] : 3.33 - 39.40 - 66.67 We have found no sharp pH optimum for phosphate uptake. It proceeds at almost constant rate till pH 6.0 and then the uptake rate drops with increasing pH. At low phosphate concentrations (1 mM) the lowest uptake rate was found at 5 and 13 °C, while the uptake is higher at 5 °C than at 13 °C at phosphate concentrations higher than 1 mM. At these concentrations uptake rate at 35 °C is lower than at 25 °C. Phosphate uptake considerably decreased in anaerobic conditions. DNP and iodoacetate (0.1 mM) completely blocked phosphate uptake from 1 mM KH₂PO₄, while uptake from 5 and 10 mM KH₂PO₄ was left unaffected by these substances. The inhibitors of active - SH groups NEM and PCMB inhibited phosphate uptake: 10^?3 M NEM by 81.6%, 10⁴ M NEM by 42% and 10^?4 M PCMB by 42%.     

Two new ion-pair complexes containing derivatives of substituted benzyl isoquinolinium and bis(maleonitriledithiolato)nickelate monoanion: 3D crystal structures, magnetic properties and theoretical analyses

Syntheses, structural characterizations, magnetic behaviors and theoretical analyses of two new ion-pair complexes, [IFBzIQl][Ni(mnt)₂](1) and [IClBzIQl]₂[Ni(mnt)₂]₂ · MeCN(2) [IFBzIQl][Ni(mnt)₂] ([IFBzIQl]⁺ = 1-(2′-fluoro-4′-iodobenzyl)isoquinolinium, [IClBzIQl]⁺ = 1-(2′-chloro-4′-iodobenzyl)isoquinolinium, mnt²⁻ = maleonitriledithiolate), have been investigated. In crystal of 1, the [Ni(mnt)₂]⁻ anions and the [IFBzIQl]⁺ cations stack into an alternating column through π?π stacking interactions. The anions of both 1 and 2 form a dimer via π?π stacking and S?S short interactions between the [Ni(mnt)₂]⁻ anions. The overlapping mode of two neighboring [Ni(mnt)₂]⁻ anions in the dimer is the Ni-ring fashion with a Ni?Ni distance of 4.076 Å for 1, and ring-ring fashion with the Ni?Ni and S?S distances being 4.395 and 3.593 Å for 2. Some weak interactions such as π?π, C?N, C-H?F or C-H?N in 1 and 2 play a crucial role in stacking and stabilizing the crystal lattice, and give a 3D network structure and exchange pathways of the magnetic interaction for 1 and 2. Magnetic susceptibility measurements for 1 and 2 in the temperature range 1.8-300 K show that the overall magnetic behavior indicates the presence of antiferromagnetic interaction, while 2 exhibits an activated magnetic behavior in the high-temperature region (HT) together with a Curie tail in the low-temperature region (LT).     

Metabolism of progesterone and testosterone by a Bacillus sp.

Microbial transformations by a Bacillus sp. were employed as a means of preparing potentially important derivatives of progesterone and testosterone. Each microbial metabolite was subjected to structure elucidation employing ¹H and ¹³C nmr, mass spectral and cd analysis. Hplc was used for the determination of the percentages of the metabolites formed. The progesterone metabolites were characterised as 14-hydroxy-4-pregnene-3,20-dione (II), 14-hydroxy-5 α -pregnane-3,6,20-trione (III)., 11 α — hydroxy-5 α — pregnane-3, 6,20-trione (IV) and 11 α, 14-dihydroxy-4-pregnene-3,20-dione (V). The testosterone analogs were identified as 4-androstene-3,17-dione (VII), 17 β-hydroxy-5 α -androstene-3,6-dione (VIII), 14-hydroxy-4-androstene-3,17-dione (IX) and 14, 17 β-dihydroxy-4-androsten -3-one (X)₁. The availability of the metabolites enabled complete elucidation of their ¹³C nmr spectra.     

Soil respiration in a Mediterranean oak forest at different developmental stages after coppicing

To assess the variation of soil respiration at different forest stages we measured it in a coppiced oak (Quercus cerris L.) chronosequence in central Italy during two campaigns, spanning 2 successive years, in four stands at different stages of the rotation: 1 year (S1), 5 years (S5), 10 years (S10) and 17 years (S17) after coppicing. The contribution of the different components of soil respiration flux (aboveground litter, belowground decomposition soil organic matter and root respiration) was estimated by a paired comparison of manipulative experiments between the recently coppiced stand (S1) and mature stand (S17). Ninety percent of soil respiration values were between 1.7 and 7.8 μmol m^?2 s^?1, with an overall mean (±SD) of 4.0±2.7 μmol m^?2 s^?1. Spatial variation of soil respiration was high (CV=44.9%), with a mean range (i.e. patch size) of 4.8±2.7 m, as estimated from a semivariance analysis. In the absence of limitation by soil moisture, soil respiration was related to soil temperature with the exponential Q₁₀ model (average Q₁₀=2.25). During summer, soil moisture constrained soil respiration and masked its dependence on soil temperature. Soil respiration declined over the years after coppicing. Assuming a linear decline with stand age, we estimated a reduction of 24% over a 20‐year‐rotation cycle. The response of soil respiration to temperature also changed with age of the stands: the Q₁₀ was estimated to decrease from 2.90 in S1 to 2.42 in S17, suggesting that different components or processes may be involved at different developmental stages. The contribution of heterotrophic respiration to total soil respiration flux was relatively larger in the young S1 stand than in the mature S17 stand.     

Biotransformation of prednisolone to hydroxy derivatives by Penicillium aurantiacum

Prednisolone, a synthetic adrenal corticosteroid drug, is known to have anti-inflammatory and autoimmune activity. Biotransformation of prednisolone was carried out to obtain more bioactive prednisolone derivatives. Among six different fungi, Penicillium aurantiacum proved to be the best prednisolone hydroxylator. As a result of prednisolone biotransformation by P. aurantiacum, whole cells four different prednisolone derivatives were investigated. 20β-Hydroxyprednisolone (1) and 21,21-dimethoxy-11β-hydroxypregn-1,4-dien-3,20-dione (2) were detected as the main metabolites. These metabolites together with other two metabolites, 11β-hydroxyandrost-1,4-dien-3,17-dione (3) and 11β,17β-dihydroxyandrost-1,4-dien-3- one (4), were purified and assigned by an interpretation of their spectral data using mass spectroscopy (MS), proton nuclear magnetic resonance (¹H-NMR), carbon nuclear magnetic resonance (¹³C-NMR) and infrared spectroscopy (IR) analyses. The best fermentation conditions for production of compounds 1–4 were as follows: medium (3) consisting of (g/l): glucose 20; l-asparagine 0.7; MgSO₄.7H₂O 0.5; KH₂PO₄ 1.52; KCl 0.52; Cu (NO₃)₂ traces; ZnSO₄.7H₂O traces, supplemented with prednisolone concentration of 0.3?mg/ml, inoculated by 10% of microorganism and incubated for 72?h. Under these optimized conditions, ～94.8% of the added prednisolone was converted to aforementioned derivatives, which have the potential to be used in industrial production of important pharmaceutical compounds.     

Endogenous Gibberellins in Elongating Shoots of Clones of Salix dasyclados and Salix viminalis

Elongating shoots of rapidly growing clones of Salix viminalis L. (clone 683-4) and Salix dasyclados Wimm. (clone 908) harvested in early August were analyzed for endogenous gibberellins (GA). Distribution of GA-like activity, determined by Tan-ginbozu dwarf rice microdrop bioassay after reverse phase C₁₈ high performance chromatography, was similar for both species. For S. dasyclados, combined gas chromatography-selected ion monotoring (GC-SIM) yielded identifications of GA₁, GA₈, GA₁₉, GA₂₀, and GA₂₉. Identifications of GA₄ and GA₉ were also made using co-injections of known amounts of [17, 17-²H₂]GAs. By bioassay, the main activity was GA₁₉-like in both species. Gibberellin A₁, GA₁₉, and GA₂₀ concentrations were approximated by GC-SIM using co-injections of known amounts of [17,17-²H₂]GAs. Both bioassay and GC-SIM results indicated very high concentrations of GA₁₉ and GA₂₀ (about 6000 nanograms per kilogram fresh weight shoot tissue using GC-SIM: 800 ng using bioassay), compared to the concentration of GA₁ (about 130 nanograms per kilogram fresh weight using either GC-SIM or bioassay).     

Crystal structures of (2R,4R)-2-(polyhydroxyalkyl)-1,3-thiazolidine-4-carboxylic acids: condensation products of l-cysteine with d-hexoses

We report herein the first crystal structures of (4-carboxy-1,3-thiazolidin-2-yl)pentitols [2-(polyhydroxyalkyl)thiazolidine-4-carboxylic acids], condensation products of l-cysteine with d-galactose and d-mannose: 2-(d-galacto-pentahydroxypentyl)thiazolidine-4-carboxylic acid hydrate, Gal-Cys·H₂O (1), and 2-(d-manno-pentahydroxypentyl)thiazolidine-4-carboxylic acid hydrate, Man-Cys·H₂O (2). In 1 and 2 the compounds crystallize as zwitterions, with the carboxylic groups deprotonated and the thiazolidine N atoms protonated. The sugar moiety and carboxylate group are in a cis configuration relative to the thiazolidinium ring, which adopts different conformation: twisted (T) on C^β–S in 1, and S-puckered envelope (E) in 2. The carbon chain of the galactosyl/mannosyl moiety remains in an extended zig-zag conformation. The orientation of the sugar O2 atom with respect to the thiazolidinium S and N atoms is trans–gauche in 1 and gauche–gauche in 2. The molecular conformation is stabilized by the intramolecular N–H?O_Cys contacts in both 1 and 2 and by the additional N–H?O_Man interaction in 2. The crystal packing of orthorhombic 1 and monoclinic 2 is determined mainly by N/O/C–H?O hydrogen bonds forming ribbons linked to each other by direct and water-mediated O/C–H?O/S contacts.     

Syntheses, structures, and magnetic properties of two new molecular magnets containing Ni(mnt)2 monoanion and substituted 4-dimethylaminopyridinium

Two new molecular magnets, [BzPyN(CH₃)₂][Ni(mnt)₂] (1) and [NO₂BzPyN(CH₃)₂][Ni(mnt)₂] (2)([BzPyN(CH₃)₂]⁺ = 1-benzyl-4-dimethylaminopyridinium, [NO₂BzPyN(CH₃)₂]⁺ = 1-(4′-nitrobenzyl)-4-dimethylaminopyridinium, and mnt²⁻ = maleonitriledithiolate) have been prepared and characterized by elemental analyses, IR, MS spectra, single crystal X-ray diffraction and magnetic susceptibility. The Ni(III) ions of both 1 and 2 form a 1D zigzag alternating magnetic chain within a column through Ni?S, Ni?Ni, Ni?N, S?S, or π?π interactions. Magnetic susceptibility measurements in the temperature range 1.8-300 K show that 1 exhibits antiferromagnetic behavior, while 2 shows a spin gap transition around 170 K, and antiferromagnetic interaction in the high-temperature phase (HT) and spin gap in the low-temperature phase (LT). The phase transition for 2 is second-order by determination of DSC analyses.     

Assessment of oxidative stress biomarkers – neuroprostanes and dihomo-isoprostanes – in the urine of elite triathletes after two weeks of moderate-altitude training

This randomized and controlled trial investigated whether the increase in elite training at different altitudes altered the oxidative stress biomarkers of the nervous system. This is the first study to investigate four F₄-neuroprostanes (F₄-NeuroPs) and four F₂-dihomo-isoprostanes (F₂-dihomo-IsoPs) quantified in 24-h urine. The quantification was carried out by ultra high pressure liquid chromatography-triple quadrupole-tandem mass spectrometry (UHPLC-QqQ-MS/MS). Sixteen elite triathletes agreed to participate in the project. They were randomized in two groups, a group submitted to altitude training (AT, n?=?8) and a group submitted to sea level training (SLT) (n?=?8), with a control group (Cg) of non-athletes (n?=?8). After the experimental period, the AT group triathletes gave significant data: 17-epi-17-F_2t-dihomo-IsoP (from 5.2?±?1.4?μg/mL 24?h^?1 to 6.6?±?0.6?μg/mL 24?h^?1), ent-7(RS)-7-F_2t-dihomo-IsoP (from 6.6?±?1.7?μg/mL 24?h^?1 to 8.6?±?0.9?μg/mL 24?h^?1), and ent-7-epi-7-F_2t-dihomo-IsoP (from 8.4?±?2.2?μg/mL 24?h^?1 to 11.3?±?1.8?μg/mL 24?h^?1) increased, while, of the neuronal degeneration-related compounds, only 10-epi-10-F_4t-NeuroP (8.4?±?1.7?μg/mL 24?h^?1) and 10-F_4t-NeuroP (5.2?±?2.9?μg/mL 24?h^?1) were detected in this group. For the Cg and SLT groups, no significant changes had occurred at the end of the two-week experimental period. Therefore, and as the main conclusion, the training at moderate altitude increased the F₄-NeuroPs- and F₂-dihomo-isoPs-related oxidative damage of the central nervous system compared to similar training at sea level.     

Effect of the cations sodium,potassium and calcium on the interaction of hyaluronate chains: a light scattering and viscometric study

Light scattering and viscometric studies have been carried out on two preparations, A and B, of rooster comb hyaluronate. Sedimentation rate studies have also been performed with A. Light scattering measurements in 0.2 m KCl for preparation A gave a molecular weight of 3.3 × 10⁶ and for B, 1.0 × 10⁶. In (0.1–0.3) M NaCl similar measurements gave a particle weight for A of (4.4–6.4 × 10⁶ and for B (1.7–2.8 × 10⁶. In 0.066 m CaCl₂ molecular weight values of 9.5 × 10⁶ for A and 1.7 × 10⁶ for B were obtained. Thus in the presence of Na⁺ and Ca²⁺ ions aggregates of chains persisted into dilute solution. Measurements by light scattering on A and B in 4 m guanidinium chloride gave values in the same range as those obtained in 0.2 m KCl. Sedimentation rate studies on A gave values of 10.3 Svedbergs in 0.2 m KCl and 12.2 Svedbergs in 0.2 m NaCl and 0.066m CaCl₂. The shear dependence of the viscosity was studied using a conicylindrical viscometer at shear rates between 0.5 and 20 s^?1. Preparation A in 0.2 m KCl and NaCl yielded values for (ν_sp/cc→0 of 5000 and 7100 ml g^?1 respectively in keeping with the tendency to aggregate. The behaviour for preparation B was similar. In 0.066 m CaCl₂ there was a marked dependence of viscosity on shear speed below 10 s^?1 for all concentrations and the value of (ν_sp/c)→0 at 0 s^?1 for preparation A was 7700 ml g^?1 while at a shear rate of 8 s^?1 (ν_sp/c)c→0 ? 5000 ml g ^?1. Similar effects were found for preparation B and the data suggest associations of chains disruptable by weak shear forces. The increase in viscosity with concentration in the presence of 0.066 m CaCl₂ was much less than in the presence of KCl or NaCl, suggesting that the Ca²⁺ had a marked effect on the ”rigidity’ of the molecules in solution. A viscometric titration experiment with Ca^2? showed that a level of 0.02 m CaCl₂ in 0.2 m NaCl was sufficient to produce the change in viscosity presented above and that significant perturbations of the viscosity were present at 0.005?0.01 m CaCl₂.     

PRIMARY PRODUCTION OF CRUSTOSE CORALLINE RED ALGAE IN A HIGH ARCTIC FJORD1

Crustose coralline algae occupied ～1%–2% (occasionally up to 7%) of the sea floor within their depth range of 15–50 m, and they were the dominant encrusting organisms and macroalgae beyond 20 m depth in Young Sound, NE Greenland. In the laboratory, oxygen microelectrodes were used to measure net photosynthesis (P) versus downwelling irradiance (E_d) and season for the two dominant corallines [Phymatolithon foecundum (Kjellman) Düwel et Wegeberg 1996 and Phymatolithon tenue (Rosenvinge) Düwel et Wegeberg 1996] representing> 90% of coralline cover. Differences in P‐E_d curves between the two species, the ice‐covered and open‐water seasons, or between specimens from 17 and 36 m depth were insignificant. The corallines were low light adapted, with compensation irradiances (E_c) averaging 0.7–1.8 μmol photons·m ^{? 2}·s ^{? 1} and light adaptation (E_k) indices averaging 7–17 μmol photons·m ^{? 2}·s ^{? 1}. Slight photoinhibition was evident in most plants at irradiances up to 160 μmol photons·m ^{? 2}·s ^{? 1}. Photosynthetic capacity (P_m) was low, averaging 43–67 mmol O₂·m ^{? 2} thallus·d ^{? 1} (～250–400 g C·m ^{? 2} thallus·yr ^{? 1}). Dark respiration rates averaged ～5 mmol O₂·m ^{? 2} thallus·d ^{? 1}. In ice covered periods, E_d at 20 m depth averaged ～1 μmol photons·m ^{? 2}·s ^{? 1}, with daily maxima of 2–3 μmol photons·m ^{? 2}·s ^{? 1}. During the open water season, E_d at 20 m depth averaged ～7 μmol photons·m ^{? 2}·s ^{? 1} with daily maxima of ～30 μmol photons·m ^{? 2}·s ^{? 1}. Significant net primary production of corallines was apparently limited to the 2–3 months with open water, and the small contribution of corallines to primary production seems due to low P_m values, low in situ irradiance, and their relatively low abundance in Young Sound.     

The enthalpy of oxidation of flavin mononucleotide

The oxidation enthalpy of reduced flavin mononucleotide at pH 7.0 in 0.2 m phosphate buffer has been studied by determining the heat associated with the reaction: FMNH₂ + 2 Fe(CN)^?3₆ ? FMN + 2 Fe(CN)^?4₆ + 2 H⁺. (a) (The quinone, semiquinone, and hydroquinone forms of FMN are represented as FMN, FMNH, and FMNH₂, respectively.) Calorimetric experiments were performed in a flow microcalorimeter which was modified to prevent sample contamination by oxygen. The enthalpy observed for reaction (a), after correction for dilution and buffer effects, was ?39.2 ± 0.4 kcal (mole FMNH₂)^?1 at 25 °C. The potential difference, ΔE′, developed by reaction (a) was determined potentiometrically and corresponded to a free energy change, ΔG′, of ?30.3 kcal (mole FMNH₂)^?1. The resulting entropy change, ΔS′, was thus calculated to be ?29.8 e.u. Reaction (a) was also studied at temperatures of 7 °C and 35.5 °C. ΔC_p′ for the reaction was calculated as ?155 ± 18 cal deg^?1 (mole FMNH₂)^?1 at 20 °C. ΔH′ for the reaction (b), FMNH₂ ? FMN + H₂, (b) was calculated as +14.2 ± 0.7 kcal mole^?1 at 25 °C, relative to the enthalpy of the hydrogen electrode being identically equal to zero at all values of pH and temperature. The free energy at pH 7.0 for reaction (b), calculated from the potential was found to be ?9.7 kcal mole^?1, which resulted in an entropy for reaction (b) of 80.2 e.u. A thermal titration of reaction (a) was used to calculate the thermodynamic parameters for the formation of semiquinone dimer according to the reaction FMNH₂ + FMN ? (·FMNH)₂. (c) The free energy, enthalpy, and entropy changes for reaction (c) were estimated to be ?6.1 kcal mole^?1, ?7 kcal mole^?1, and ?3 e.u., respectively.     

A LIMNOLOGICAL PROFILE OF THE UPPER OKAVANGO DELTA AT LOW WATER LEVEL

Summary

Selected limnological attributes of the Okavango Delta panhandle were measured during a brief summer survey of “open-water” habitats extending from the permanent mainstream channel, through contiguous off-channel lagoons and still backwaters, to seasonally isolated floodplain lagoon and temporary pool biotopes on the left-bank of the Okavango River at Seronga.

Wide ranges in most determinants were evident along this profile:- temperature (27–34°C); conductivity(4–12.7mS m^?1); pH(5.7–9.2); transparency(0.2–>2.5 m Secchi depth); dissolved oxygen (20–220% saturation); PO₄-P (61–110 μg ?^?1): SiO₂—Si (6.9–14.0 mg ?^?1): NH₄-N (30–44 μg ?^?1): chlorophyll (1.3–183 μ.g ?^?1). Zooplankton was variably diverse (species richness from ≥ 3 to 20), comprising both euplanktonic (Bosmina, Ceriodaphnia, Daphnia, Diaphanosoma, Moina, Mesocyclops, Thermocyclops, Tropodiaptomus) and more typical epiphytic crustacean taxa (Alona, Macrothrix, Pleuroxus), along with various rotifers (Brachionus, Hexarthra, Keratella, Trichocera) and other taxa (Arcella, Ostracoda. Chaoborus). Abundance varied widely between habitats. The littoral macrozoobenthos showed surprisingly low diversity, and was dominated by freshwater shrimps (Caridina).

Substantial allochthonous inputs to the Okavango swamps were evident from the significant concentrations of total suspended solids (7.6–12.6 mg ?^?1 , organic content of 33–41%) carried by the mainstream Okavango River during the survey.