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1.
Summary. The influence of the operation conditions (temperature and residence time) of a thermic treatment on the total amount (free
and protein-bound) of amino acid enantiomers of dry fullfat soya was investigated. Total amino acid content was determined
using conventional ion-exchange amino acid analysis of total hydrolysates and chiral amino acid analysis was performed by
HPLC after precolumn derivatization with o-phthaldialdehyde and 1-thio-β-D-glucose tetraacetate. Contrary to corn that was investigated previously, notable racemization
was detected even at lower temperatures. At 140 °C the ratio of the D-enantiomer was 0.87% for glutamic acid, 2.81% for serine,
and 1.92% for phenylalanine; at 220 °C the ratios of the D-enantiomer of the above amino acids were 1.43, 4.61, and 4.68%,
respectively. The concentration of several L-amino acids decreased. At 220 °C there was 10% less L-glutamic acid, 17% less
L-serine, 5% less L-phenylalanine, 6.6% less L-aspartic, acid and 21% less L-lysine than in the control; their loss can be
assigned to different degrees of L – D conversion. While nearly complete transformation of L-phenylalanine can be attributed
to racemization, the main cause of the loss of L-lysine is not racemization. The treatments in the same order of magnitude
resulted in the formation of more D-amino acids and greater extent of racemization of amino acids in fullfat soya than that
of maize.
Authors’ address: J. Csapó, Faculty of Animal Science, Institute of Chemistry, University of Kaposvár, Guba S. u. 40., H-7400
Kaposvár, Hungary 相似文献
2.
Summary. 6-N-carboxymethyllysine (CML), generated by the glycation and/or oxidation of lysine residues, has been measured in biological
materials and food products using techniques such as ELISA, HPLC with fluorescence detection and mass spectrometry methods.
Only limited information has been reported regarding the preparation of standards labeled with either deuterium, 13C or 15N atoms to be used as internal standards. In the present paper, a synthesis of carbon-13 labeled CML is described using l,2-13C2-glyoxylic acid and 2-N-acetyllysine as starting materials. The resulting labeled 2-N-acetyl-CML was purified by HPLC-UV as a dibutyl ester. After a deprotection step, the yield was evaluated to be 53% when
the reaction was conducted 17 h at 37°C. CML was extensively studied by 1H- and 13C-NMR and the fragments observed in the collision induced dissociation (CID) spectrum were also assigned. Finally, the standards
of CML and carbon-13 labeled CML were accurately quantified based on 1H-NMR and tandem MS using lysine as an internal reference. 相似文献
3.
Summary. Spore coat-associated alanine racemase of Bacillus subtilis, which converts L-alanine to D-alanine, that is, the germinant to the competitive inhibitor, to regulate spore germination
for survival of the organism under unfavorable growth conditions, was examined. The dormant spores, L-alanine-initiated germination
of which is inhibited by diphenylamine, were used to characterize the enzyme in the native form because of its unextractablility
from dormant spores. The presence of isozymes, Enz-I and Enz-II with Km for L-alanine of about 20 mM and 50 mM and optimum
activity at around 40°C and 65°C, respectively, was proposed. The enzymes were selectively used depending on the L-alanine
concentration and the temperature. The pH profiles of the activity (optimun at pH 9.0) and the stability (stable between pH
6–11 at 60°C) were similar, but Enz-II was more heat-stable than Enz-I and the denaturation curve demonstrated a two-domain
structure for Enz-II. Sensitivity to D-penicillamine, hydroxylamine and HgCl2 was similar between Enz-I and Enz-II, while that to D-cycloserine, L- and D-aminoethylphosphonic acid, monoiodoacetate and
N-ethylmaleimide was different; HgCl2 was the most effective inhibitor among these compounds.
Received December 13, 1999, Accepted January 11, 2000 相似文献
4.
Michael Wille Henry Hooghiemstra Hermann Behling Klaas van der Borg Alvora Jose Negret 《Vegetation History and Archaeobotany》2001,10(2):61-77
We present a reconstruction of forest history and climatic change based on 11 pollen records from eight sites, all located
in the lower montane forest belt of the northern Andes in Colombia. We compared records from the Popayán area in southern
Colobia, Timbio (1750 m), Genagra (1750 m) and Pitalito (1300 m) and the new Piagua (1700 m) record with the records from
Lusitania (1500 m), Libano (1820 m), Pedro Palo (2000 m) and Ubaqué (2000 m) from Central Colombia. The changes of the altitudinal
position of the lower/upper montane (= subandean/Andean, S/At) forest belt transition were used to estimate temperature change
for the last 50 kyr. We infer a Last Glacial Maximum (LGM) temperature drop of 6°–7°C at 1700 m, and a steeper LGM lapse rate
of 0.76°C/100 m compared to today (ca. 0.6°C/100 m). Around 50 uncal. kyr B.P. the temperature at 1700 m was ca. 3°C lower
than today. Until 20 uncal. kyr B.P. the temperature oscillated and gradually decreased. During the LGM, temperature was down
to ca. 6°–7°C lower than today. After the LGM, temperature increased and ca. 14 uncal. kyr B.P. it was 2°–3°C lower than today
(S/At at ca. 1800 m, 500 m below present elevation; Susacá interstadial). An unquantified cooling (Ciega stadial) followed.
During ca. 12.3–11.7 uncal. kyr B.P. the S/At shifted upslope to 2100 m indicating a temperature of 1°–2°C cooler than today
(Guantiva interstadial). From 11.7–10.9 uncal. kyr B.P. the S/At was at 1800 m indicating that the temperature was ca. 3°C
lower than today and wet conditions prevailed (partly coinciding with the El Abra stadial). The period 10.9–9 uncal. kyr B.P.
was also cool, but drier. During 9–7.5 uncal. kyr B.P. temperature was ca. 1°C warmer relative to today (mid Holocene hypsithermal).
During the last 5 kyr the presence of cultivated plants demonstates human colonization of the lower montane zone in Colombia.
Received June 14, 2000 / Accepted December 19, 2000 相似文献
5.
The peptide bond formation of alanine (ala), ala + glycine (gly), ala + diglycine (gly2), and ala + gly cyclic anhydride (cyc-gly2) in drying/wetting cycles at 80°C was studied. Silica, alumina, and representative smectites—montmorillonite and hectorite—were
used as catalysts, and the dependence of reaction yields on the available amount of water in the reaction systems was evaluated.
Silica and alumina catalyze the formation of oligopeptide mainly in temperature fluctuation experiments, whereas higher amounts
of water in the reaction system support clay-catalyzed reactions. Silica and alumina are much more efficient for amino acid
dimerization than clays. Whereas only 0.1% of ala oligomerized on hectorite and no reaction proceeded on montmorillonite,
about 0.9 and 3.8% alanine converted into its dimer and cyclic anhydride on silica and alumina, respectively. Clay minerals,
on the other hand, seem to more efficiently catalyze peptide chain elongation than amino acid dimerization. The reaction yields
of ala-gly-gly and gly-gly-ala from ala + gly2 and ala + cyc-gly2 reached about 0.3% on montmorillonite and 1.0% on hectorite. The possible mechanisms of these reactions and the relevance
of the results for prebiotic chemistry are discussed.
Received: 15 December 1996 / Accepted: 1 May 1997 相似文献
6.
Summary. Two Lys–Lys crosslinks, 1,3-bis-(5-amino-5-carboxypentyl)-1H-imidazolium (GOLD) and 1,3-bis(5-amino-5-carboxypentyl)-4-methyl-1H-imidazolium
(MOLD) salts, have been synthesized by the reaction of imidazole or 4(5)-methyl imidazole with 5-(4-bromobutyl)-hydantoin
followed by the hydrolysis of 1,3-substituted imidazolium derivatives by 6.0 N HCL at 110 °C. Treatment of GOLD and MOLD with
hydrogen peroxide in acetic acid leads to MOLD oxidation only. The oxidation product of MOLD was detected in cataractous lens
proteins. 相似文献
7.
Summary. In this study, we found that two amino acids reacted with 2,5-hexanedione to form new reaction products in vitro, respectively.
In the reaction of beta-alanine and 2,5-hexanedione, a reaction product was obtained and analyses of obtained results showed
it was 3-(2,5-dimethyl-1H-pyrrol-1-yl)propanoic acid; in the reaction of glycine and 2,5-hexanedione, a reaction product was also obtained and analyses
showed it was (2,5-dimethyl-1H-pyrrol-1-yl)acetic acid. Two reaction products were found to be oxidized easily; in addition, the latter was more easily
to be oxidized than the former in the air. Our discoveries demonstrated that reactions between amino acids and 2,5-hexanedione
could exist possibly in vitro. At present, it is clear that 2,5-hexanedione causes either axon atrophy or swelling, but the
underlying molecular mechanism is still unclear. Since both beta-alanine and glycine are considered as neurotransmitter in
the central nervous system, the reaction products remain to be identified in vivo. 相似文献
8.
The effect of extractants on degradation of L-glutamate and L-arginine in the course of shaking and filtration at low temperature 总被引:1,自引:0,他引:1
Summary. The effects of demineralized water (DEMI H2O) and 0.5 M ammonium acetate (0.5 M AAc) on losses of L-glutamic acid and L-arginine in the course of shaking and filtration
at low temperature (6 °C) were tested. The concentration of L-glutamic acid decreased by 6.3% in DEMI H2O and by 4.9% in 0.5 M AAc, whereas the L-arginine concentration decreased by 6.0% (DEMI H2O) and 10.7% (0.5 M AAc). We found a significantly (P < 0.05) higher degradation of L-arginine in 0.5 M AAc compared with that of DEMI H2O. 相似文献
9.
Kocsy G von Ballmoos P Suter M Rüegsegger A Galli U Szalai G Galiba G Brunold C 《Planta》2000,211(4):528-536
The role of glutathione (GSH) in protecting plants from chilling injury was analyzed in seedlings of a chilling-tolerant
maize (Zea mays L.) genotype using buthionine sulfoximine (BSO), a specific inhibitor of γ-glutamylcysteine (γEC) synthetase, the first enzyme
of GSH synthesis. At 25 °C, 1 mM BSO significantly increased cysteine and reduced GSH content and GSH reductase (GR: EC 1.6.4.2)
activity, but interestingly affected neither fresh weight nor dry weight nor relative injury. Application of BSO up to 1 mM
during chilling at 5 °C reduced the fresh and dry weights of shoots and roots and increased relative injury from 10 to almost
40%. Buthionine sulfoximine also induced a decrease in GR activity of 90 and 40% in roots and shoots, respectively. Addition
of GSH or γEC together with BSO to the nutrient solution protected the seedlings from the BSO effect by increasing the levels
of GSH and GR activity in roots and shoots. During chilling, the level of abscisic acid increased both in controls and BSO-treated
seedlings and decreased after chilling in roots and shoots of the controls and in the roots of BSO-treated seedlings, but
increased in their shoots. Taken together, our results show that BSO did not reduce chilling tolerance of the maize genotype
analyzed by inhibiting abscisic acid accumulation but by establishing a low level of GSH, which also induced a decrease in
GR activity.
Received: 9 November 1999 / Accepted: 17 February 2000 相似文献
10.
Summary. Heat shock proteins (HSPs) are synthesised by cells subsequent to a stress exposure and are known to confer protection to
the cell in response to a second challenge. HSP induction and decay are correlated to thermotolerance and may therefore be
used as a biomarker of thermal history. The current study tested the temperature-dependent nature of the heat shock response
and characterised its time profile of induction. Whole blood from 6 healthy males (Age: 26 ± (SD) 2 yrs; Body mass 74.2 ±
3.8 kgs; VO2max: 49.1 ± 4.0 ml·kg−1·min−1) were isolated and exposed to in vitro heat shock (HS) at 37, 38, 39, 40, and 41 °C for a period of 90 min. After HS the
temperature was returned to 37 °C and intracellular HSP70 was quantified from the leukocytes at 0, 2, 4, and 6 h after heat
treatment. The concentration of HSP70 was not different between temperatures (P > 0.05), but the time-profile of HSP70 synthesis appeared temperature-dependent. At control (37 °C) and lower temperatures
(38–39 °C) the mean HSP70 concentration increased up to 4 h post HS (P < 0.05) and then returned towards baseline values by 6 h post HS. With in vitro hyperthermic conditions (40–41 °C), the time-profile
was characterised by a sharp rise in HSP70 levels immediately after treatment (P < 0.05 for 40 °C at 0 h), followed by a progressive decline over time. The results suggest a temperature-dependent time-profile
of HSP70 synthesis. In addition, the temperature at which HSP70 is inducted might be lower than 37 °C. 相似文献
11.
Anne-Marie Lézine Jean-François Saliège Robert Mathieu Thibaut-Louis Tagliatela Sophie Mery Vincent Charpentier Serge Cleuziou 《Vegetation History and Archaeobotany》2002,11(3):221-232
Pollen and micropalaeontological analyses carried out on mangrove swamp sediments of Suwayh, Oman (22°05.589'N, 50°40.033'E)
reveal environmental changes linked both to climate (monsoon) and geomorphological (sea-level) variations during the Late
Holocene. A Rhizophora mangrove developed at Suwayh around 6000 years B. P. under climate conditions marked by an increased tropical influence as
compared to the modern situation, with dominant summer rains. The later extension of Prosopis cineraria at Suwayh provides evidence for a different rainfall pattern, with a winter rainy season. Pollen and micropalaeontological
composition shows three episodes influenced by the sea water at Suwayh. The most important corresponded to the mangrove episode
centred ca 6000 B. P. This was followed by two episodes of slight seawater incursion at ca. 5100 and 4500 B. P. responsible
for the formation of a brackish laagon. Comparison based on 14C measurements on shell recovered from both the sedimentary sequence of Suwayh and the nearby archaeological sites demonstrates
that close relations existed between man and mangroves during the Neolithic and the Early Bronze Age.
Received October 31, 2001 / Accepted January 24, 2002
Correspondence to: Anne-Marie Lézine 相似文献
12.
Sang Woo Baek Jun Seok Kim Yoon Kook Park Young Soo Kim Kyeong Keun Oh 《Biotechnology and Bioprocess Engineering》2008,13(3):332-341
A batch reactor was used to investigate the dilute acid hydrolysis reaction of alpha-cellulose and sugar decomposition reactions.
Varying the sulfuric acid concentration from 0.07 to 5.0% for reaction temperatures between 180 and 220°C significantly affected
glucose yields, which ranged from about 70% to below 10%. Increasing the reaction temperature enhanced this effect. Similar
experimental results were obtained for the decomposition of xylose. For sugar decomposition reactions, less than 0.3 g/L of
furfural and 5-hydroxymethylfurfural (5-HMF) were produced from glucose and xylose in the absence of sulfuric acid at 190°C
and 15 min of reaction time, but adding a small amount of sulfuric acid (0.5%) dramatically increased the decomposition rate
and led to the formation of four undesireable products: formic acid, 5-HMF, acetic acid, and furfural. In both hydrolysis
and fermentation reactions formic acid, acetic acid, and 5-HMF severely inhibited ethanol fermentation, while furfural had
less of an inhibition effect. 相似文献
13.
Undheim K 《Amino acids》2008,34(3):357-402
The focus has been on the development of methodology for stereoselective preparation of spiroannulated intermediates of the Sch?llkopf chiron and further transformations to cyclic alpha-amino acids. The spiroannulations are effected by Ru(II)-catalysed ring-closing metathesis reactions, by Ru(II)- and Pd(0)-catalysed cycloisomerisations, by Rh(II)-carbenoid cyclisation reactions and by intramolecular aldol condensations. Hydrolytic reactions of the spirane intermediates have provided several groups of highly novel and functionalised five-, six- and seven-membered cyclic alpha-quaternary-alpha-amino acid derivatives as well as alicyclic derivatives. The novel cyclic amino acid derivatives can be regarded as cyclic constrained analogues of corresponding common amino acids, or in some cases as intermediates for further preparation of such amino acids. Some emphasis has been on the preparation of cyclic serine analogues. Major efforts have been on the preparation of cyclic alpha-quaternary bis(alpha-amino acid) derivatives as conformationally constrained dicarba-analogues of cystine. 相似文献
14.
Summary. Glutamine is one of the most abundant free amino acid found in raw food. In this study, the contribution of free glutamine
to nonenzymatic browning and fluorescence was investigated using an aqueous model system with methylglyoxal. The results indicated
that glutamine contributed to the Maillard reaction via two pathways. First, the hydrolysis of the amide bond of glutamine
led to the release of ammonia which was implicated in the formation of brown color and fluorescence. Among other nitrogen
donors tested (asparagine, glutamic acid and urea) our results demonstrated that free glutamine was a major source of ammonia
during heating. When heated at 120 and 180 °C, 100% of ammonia was released from glutamine after 60 and 10 min, respectively.
The second pathway involved a direct Maillard reaction with the α-amino group of glutamine. Both pathways led to a rapid and
complete destruction of glutamine when heated in the model systems. With reference to the Maillard browning (absorbance at
420 nm) glutamine turned out to be the most reactive amine, followed by asparagine, glutamate, ammonia and urea. Maximum fluorescence
(excitation and emission wavelengths at 330 and 450 nm, respectively) was also observed with glutamine followed by urea and
ammonia. Overall this study suggested that free glutamine predominantly contributes to the color and fluorescence formations
of foodstuffs. 相似文献
15.
Nitric oxide stimulates seed germination and de-etiolation, and inhibits hypocotyl elongation, three light-inducible responses in plants 总被引:46,自引:0,他引:46
Seed germination, greening of etiolated plants and inhibition of hypocotyl elongation are stimulated by light, which is sensed
by various types of photoreceptor. Nitric oxide (NO) has proven to be a bioactive molecule, especially in mammalian cells
and, most recently, in plants. Like some phytochrome-dependent processes, many NO-mediated ones are accomplished through increases
in cGMP levels. Given these similarities, we proposed that NO could take part in light-mediated events in plants. Here we
show that NO promotes seed germination and de-etiolation, and inhibits hypocotyl and internode elongation, processes mediated
by light. Two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine induced germination of lettuce (Lactuca sativa L. cv. Grand Rapids) seeds in conditions in which this process is dependent on light (e.g. 26 °C). This was a dose-dependent
response and was arrested by addition of an NO scavenger, carboxy-PTIO. In addition, nitrite and nitrate, two NO-decomposition
products were ineffective in stimulating germination. Wheat seedlings sprayed with SNP and grown in darkness contained 30–40%
more chlorophyll than control seedlings. Nitric-oxide-mediated partial greening was increased by light pulses, wounding and
biotic stress. Arabidopsis thaliana (L.) Heynh. (ecotype Columbia) and lettuce seedlings grown in the dark had 20%-shorter hypocotyls in NO treatments than in
control ones. On the other hand, internode lengths of potato plants growing under low light intensity and sprayed with 100 μM
SNP were also 20% shorter than control ones. These results implicate NO as a stimulator molecule in plant photomorphogenesis,
either dependent on or independent of plant photoreceptors.
Received: 27 April 1999 / Accepted: 16 June 1999 相似文献
16.
Docosahexaenoic acid is found to be bound to three equivalent sites on albumin with the same affinities as palmitic acid
at 0–38°C, which demonstrates that ethene-1,2-diyl- and methylene-groups contribute equally to the affinity. The equilibrium
dissociation constants (K
dm
s) for red cell membrane binding sites of linoleic- and docosahexaenoic acid at pH 7.3 are determined at temperatures between
0 and 37°C. The temperature-independent capacities for binding are 12 ± 1 and 25.4 ± 3.0 nmoles g−1 ghosts respectively. Double isotope binding experiments reveal that the unsaturated fatty acids: arachidonic-, linoleic-,
docosahexaenoic-, and oleic acid have partially shared capacities in ratios approximately 1:2:4:5, in contrast to the noncompetitive
binding of palmitic acid. The observations suggest a two-tier binding limitation. One is the number of protein sites binding
fatty acid anions electrostatically and the other is the number of suitable annular lipids adaptively selected among membrane
lipids by the hydrocarbon chain. These competition conditions are confirmed by measurements of the tracer exchange efflux
at near 0°C from albumin-free and albumin-filled ghosts of linoleic- and docosahexaenoic acid, either alone or in the presence
of arachidonic- and palmitic acid. Under equilibrium conditions, the calculated ratios of inside to outside membrane binding
is below 0.5 for four unsaturated fatty acids. The unidirectional rate constants of translocation between the inside and the
outside correlate with the number of double bonds in these fatty acids, which are also correlated with the dissociation rate
constants of the complexes with albumin. The membrane permeation occurs presumably by binding of the anionic unsaturated fatty
acids to an integral protein followed by channeling of the neutral form between opposite binding sites of the protein through
annular lipids encircling the protein.
Received: 30 June 1997/Revised: 23 February 1998 相似文献
17.
Summary. New bioinorganic complexes of the aspartic acid with the antimony or bismuth triiodide were synthesized by a direct solid–solid
reaction at room temperature. The formula of the complex is MI3[OOCCH2CH(NH2)CO]2.5 · 2.5H2O (M = Sb, Bi). The complex may be a dimer with bridge structure. The crystal structure of the complexes belongs to a triclinic
system. The lattice parameters are a = 0.9883 nm, b = 1.4284 nm, c = 2.0114 nm, α = 94.46°, β = 99.76° and γ = 100.1° for
the complex of antimony and a = 0.9756 nm, b = 1.4560 nm, c = 1.9875 nm, α = 94.18°, β = 97.25° and γ = 101.16° for the complex
of bismuth. The infrared spectra and thermal analyses can demonstrate the complex formation between the aspartic acid and
the antimony or bismuth ion. 相似文献
18.
Hybrid lethality expressed in the interspecific hybrid of Nicotiana suaveolens Lehm. ×N. tabacum L. cv. Hicks-2 is one of the mechanisms for reproductive isolation and it is temperature-sensitive. Apoptotic changes were
detected in the cells of hybrid seedlings and calli expressing lethality at 28 °C but not under high-temperature conditions
(36 °C), when the lethality is suppressed. Condensation of chromatin, fragmentation of nuclei and cytoplasmic reduction are
the cytological changes associated with apoptosis leading to hybrid lethality. Fragmentation of nuclei was correlated with
the lethal symptoms in both hybrid seedlings and calli, as confirmed by fluorimetry of the nuclear DNA using laser scanning
cytometry. Agarose gel analysis of DNA extracted from hybrid seedlings and calli showing lethal symptoms revealed a specific
ladder pattern suggesting nucleosomal fragmentation which is one of the biochemical changes of apoptosis. In-situ detection
using terminal deoxyribonucleotidyl transferase-mediated dUTP-fluorescein nick end labeling (TUNEL) showed that this process
occurred in distinct stages on each organ of hybrid seedlings and centripetally in hybrid calli. From these results, we confirmed
that cell death inducing hybrid lethality was indeed apoptosis.
Received: 23 December 1999 / Accepted: 5 April 2000 相似文献
19.
Agostinelli E Tempera G Molinari A Salvi M Battaglia V Toninello A Arancia G 《Amino acids》2007,33(2):175-187
Summary. In tumours, polyamines and amine oxidases increase as compared to normal tissues. Cytotoxicity induced by bovine serum amine
oxidase (BSAO) and spermine is attributed to H2O2 and aldehydes produced by the reaction. Increasing the incubation temperature from 37 to 42 °C enhances cytotoxicity in cells
exposed to spermine metabolites. The combination BSAO/spermine prevents tumour growth, particularly well if the enzyme has
been conjugated with a biocompatible hydrogel polymer. Since the tumour cells release endogenous substrates of BSAO, the administration
of spermine is not required. Combination with hyperthermia improves the cytocidal effect of polyamines oxidation products.
Our findings show that multidrug resistant (MDR) cells are more sensitive to spermine metabolites than their wild-type counterparts,
due to an increased mitochondrial activity which induces the generation of intracellular ROS prior to the onset of mitochondrial
permeability transition (MPT). It makes this new approach attractive, since the development of MDR is one of the major problems
of conventional cancer therapy. 相似文献
20.
We have studied binding and membrane transfer rates of unsaturated long-chain fatty acids in sheep red cells, as previously
done for human red cells, in order to elucidate the transport mechanism. Observed differences must be assigned to the different
composition of the membrane in the two species.
Equal surface areas of the membranes of the two species have similar binding capacities and affinities for palmitic-, linoleic-,
oleic- and arachidonic acid at 37°C. The competitive bindings of linoleic- and arachidonic acid as well as the distribution
of bound arachidonic acid on the two sides of the membrane are not different in the two species. However, the rate constants
for membrane transfer in sheep are less than half of those measured previously for human ghosts. This finding is confirmed
by the exchange efflux kinetics of ghosts containing albumin-bound fatty acid. Studies of sheep ghost membranes with oleic-,
arachidonic- and linoleic acid reveal a proportionality between the membrane transfer rate constants and the number of fatty
acid double bonds, as found previously for human ghost membrane, and the effect of double bonds is in harmony with a large
negative activation entropy for diffusion through the membrane. The established replacement of lecithin by sphingomyelin with
a low unsaturation fatty acid index in sheep membranes probably causes a lower transversal lipid phase fluidity. Double bonds
diminish the flexibility of hydrocarbon chains and thus the large negative activation entropy of diffusion across the membrane.
The smaller transfer rate constants of the three unsaturated fatty acids in sheep membranes support the hypothesis that the
transfer is diffusion in protein defined annular lipid domains and not carrier mediated.
Received: 24 February 1999/Revised: 10 June 1999 相似文献