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51.
Candida bombicola ATCC 22214 produces the glycolipid sophoroselipid when cultivated on a medium with glucose as the sole carbon source. Under
phosphate-limiting conditions the product yield rises from 0.033 to 0.143 and the specific product formation rate rises from
0.004 h-1 to 0.007 h-1. Enhanced sophoroselipid synthesis is initiated by the decline of the specific activities of NAD- and NADP-dependent isocitrate
dehydrogenase (EC 1.1.1.41 and 1.1.1.42) to 2% and 0% of the initial activities respectively. Constantly high specific activity
of citrate synthase (EC 4.1.3.7) causes an accumulation of isocitrate and citrate in the mitochondria. Both acids are transported
into the cytosol where citrate is cleaved by ATP: citrate lyase (EC 4.1.3.8) giving rise to acetyl-CoA, the precursor of fatty
acid synthesis. The ATP: citrate lyase is unaffected by different energy charges; the apparent K
m values for coenzyme A, ATP and citrate are 23 μM, 250 μM and 256 μM respectively. NADPH for fatty acid synthesis might be
generated by further metabolism of oxaloacetate, the other product of the citrate-cleaving reaction, by oxidation of the isocitrate
by the cytosolic NADP-dependent isocitrate dehydrogenase or via the hexose monophosphate shunt. A possible explanation for
sophoroselipid formation during exponential growth is given.
Received: 7 November 1995/Received revision: 19 March 1996/Accepted: 25 March 1996 相似文献
52.
Matthias Laska 《Primates; journal of primatology》1996,37(4):457-465
The purpose of this study was to test the influence of sex, age, social rank, matriline membership, posture, and visual and
tactual motor control on manual preferences inSaimiri sciureus. A well-established social group of 12 squirrel monkeys, aged 2 to 14 yrs and consisting of two matrilines with social rank
known for each animal, was presented with four different food-reaching tasks and assessed for hand preferences with a minimum
of 100 reaches per animal.
Frequency of occurrence of hand preferences at the group level and degree of hand preferences at the individual level depended
on posture and on whether the reaching act took place under visual or tactual guidance. Sex, age, social rank, and matriline
membership were not found to determine frequency of occurrence, direction or degree of hand preferences with the exception
of one task in which a significant negative correlation between the degree of hand preference and age was found. Nine out
of 12 monkeys showed task-dependent changes in the hand they used preferentially while only three animals preferred the same
hand in all four tasks. Significant preferences for the use of right or left hand on a given task were distributed almost
equally between individuals. Thus, the results of this study suggest task-specific demands like posture and/or whether reaching
was visually or tactually guided to be the major correlates of hand preferences in food-reaching tasks in squirrel monkeys. 相似文献
53.
Folkert Reck Ernst Meinjohanns Matthias Springer Roland Wilkens Johannes A. L. M. Van Dorst Hans Paulsen Gabriele Möller Inka Brockhausen Harry Schachter 《Glycoconjugate journal》1994,11(3):210-216
UDP-GlcNAc: Man1-6R (1-2)-N-acetylglucosaminyltransferase II (GlcNAc-T II; EC 2.4.1.143) is a key enzyme in the synthesis of complexN-glycans. We have tested a series of synthetic analogues of the substrate Man1-6(GlcNAc1-2Man1-3)Man-O-octyl as substrates and inhibitors for rat liver GlcNAc-T II. The enzyme attachesN-acetylglucosamine in 1-2 linkage to the 2-OH of the Man1-6 residue. The 2-deoxy analogue is a competitive inhibitor (K
i=0.13mm). The 2-O-methyl compound does not bind to the enzyme presumably due to steric hindrance. The 3-, 4- and 6-OH groups are not essential for binding or catalysis since the 3-, 4- and 6-deoxy and -O-methyl derivatives are all good substrates. Increasing the size of the substituent at the 3-position to pentyl and substituted pentyl groups causes competitive inhibition (K
i=1.0–2.5mm). We have taken advantage of this effect to synthesize two potentially irreversible GlcNAc-T II inhibitors containing a photolabile 3-O-(4,4-azo)pentyl group and a 3-O-(5-iodoacetamido)pentyl group respectively. The data indicate that none of the hydroxyls of the Man1-6 residue are essential for binding although the 2- and 3-OH face the catalytic site of the enzyme. The 4-OH group of the Man-O-octyl residue is not essential for binding or catalysis since the 4-deoxy derivative is a good substrate; the 4-O-methyl derivative does not bind. This contrasts with GlcNAc-T I which cannot bind to the 4-deoxy-Man- substrate analogue. The data are compatible with our previous observations that a bisectingN-acetylglucosamine at the 4-OH position prevents both GlcNAc-T I and GlcNAc-T II catalysis. However, in the case of GlcNAc-T II, the bisectingN-acetylglucosamine prevents binding due to steric hindrance rather than to removal of an essential OH group. The 3-OH of the Man1-3 is an essential group for GlcNAc-T II since the 3-deoxy derivative does not bind to the enzyme. The trisaccharide GlcNAc1-2Man1-3Man-O-octyl is a good inhibitor (K
i=0.9mm). The above data together with previous studies indicate that binding of the GlcNAc1-2Man1-3Man- arm of the branched substrate to the enzyme is essential for catalysis.
Abbreviations: GlcNAc-T I, UDP-GlcNAc:Man1-3R (1-2)-N-acetylglucosaminyltransferase I (EC 2.4.1.101); GlcNAc-T II, UDP-GlcNAc:Man1-6R (1-2)-N-acetylglucosaminyltransferase II (EC 2.4.1.143); MES, 2-(N-morpholino)ethane sulfonic acid monohydrate. 相似文献
54.
Gellerich Frank Norbert Kapischke Matthias Kunz Wolfram Neumann Wolfram Kuznetsov Andrey Brdiczka Dieter Nicolay Klaas 《Molecular and cellular biochemistry》1994,133(1):85-104
Summary Cytosolic proteins as components of the physiological mitochondrial environment were substituted by dextrans added to media normally used for incubation of isolated mitochondria. Under these conditions the volume of the intermembrane space decreases and the contact sites between the both mitochondrial membranes increase drastically. These morphological changes are accompanied by a reduced permeability of the mitochondrial outer compartment for adenine nucleotides as it was shown by extensive kinetic studies of mitochondrial enzymes (oxidative phosphorylation, mi-creatine kinase, mi-adenylate kinase). The decreased permeability of the mitochondrial outer membrane causes increased rate dependent concentration gradients in the micromolar range for adenine nucleotides between the intermembrane space and the extramitochondrial space. Although all metabolites crossing the outer membrane exhibit the same concentration gradients, considerable compartmentations are detectable for ADP only due to its low extramitochondrial concentration. The consequences of ADP-compartmentation in the mitochondrial intermembrane space for ADP-channelling into the mitochondria are discussed. 相似文献
55.
56.
Egbert J. Boekema Arjen F. Boonstra Jan P. Dekker Matthias Rögner 《Journal of bioenergetics and biomembranes》1994,26(1):17-29
Electron microscopy (EM) in combination with image analysis is a powerful technique to study protein structure at low- and high resolution. Since electron micrographs of biological objects are very noisy, substantial improvement of image quality can be obtained by averaging individual projections. Crystallographic and noncrystallographic averaging methods are available and have been applied to study projections of the large protein complexes embedded in photosynthetic membranes from cyanobacteria and higher plants. Results of EM on monomeric and trimeric Photosystem I complexes, on monomeric and dimeric Photosystem II complexes, and on the monomeric cytochromeb6/f complex are discussed. 相似文献
57.
A male patient carrying an interstitial deletion in Xp22.3 and affected by Kallmann syndrome, X-linked ichthyosis and mental retardation, but without chondrodysplasia punctata or short stature, was investigated with molecular probes from the distal Xp22.3 region. By means of a novel probe, M115, from the relevant region, the distal deletion breakpoint was shown to be between 3.18 and 3.57 Mb from Xptel. As the patient is not affected by X-linked recessive chondrodysplasia punctata, the gene for this disease can therefore be located to within an interval of less than one megabase proximal to the pseudoautosomal boundary. If the chondrodysplasia punctata gene is associated with a CpG island, this leaves only two islands at 2760 and 3180 kb from the Xp telomere as the most promising candidate sites for this gene. 相似文献
58.
Matthias Liebergesell Alexander Steinbüchel 《Applied microbiology and biotechnology》1993,38(4):493-501
From a genomic library of Thiocystis violaceae strain 2311 in L47, two adjacent EcoRI restriction fragments of 5361 base pairs (bp) and of 1978 bp were cloned. The 5361-bp EcoRI restriction fragment hybridized with a DNA fragment harbouring the Alcaligenes eutrophus poly(3-hydroxyalkanoate) (PHA) synthase operon (phbCAB) and restored the ability to synthesize and accumulate PHA in PHA-negative mutants derived from A. eutrophus. The nucleotide sequence analysis of both fragments revealed five open-reading frames (ORFs); at least three of them are probably relevant for PHA biosynthesis. The amino acid sequences of the putative proteins deduced from these genes indicate that they encode a -ketothiolase [phbA
Tv, relative molecular mass (Mr) 40850], which exhibited 87.3% amino acid identify with the -ketothiolase from Chromatium vinosum. The amino acid sequences of the putative proteins deduced from ORF2Tv (Mr 41 450) and phbC
Tv (Mr 39 550), which were located upstream of and antilinear to phbA
Tv, exhibited 74.7% and 87.6% amino acid identify, respectively, with the corresponding gene products of C. vinosum. Downstream of and antilinear to phbC
Tv was located ORF5, which encodes for a protein of high relative molecular mass (Mr 76428) of unknown function. With respect to the divergent organisation of ORF2Tv and phbC
Tv on one side and of phbA
Tv on the other side and from the homologies of the putative gene products, this region of the T. violaceae genome resembled very much the corresponding region of C. vinosum, which was identified recently.
Correspondence to: A. Steinbüchel 相似文献
59.
60.
Photosynthesis has been determined with mutants of Anacystis which form different amounts of carotenoids. With these cultures a highly significant correlation between photosynthetic oxygen evolution and the amounts of synthesized carotenoids was observed. In addition, the influence of carotenoids on light-dependent degradation of thylakoid proteins was investigated with Scenedesmus cultures grown in darkness in the presence of norflurazon, an inhibitor of carotenoid biosynthesis. Pre-illumination of cells resulted in decrease of photosynthetic activity accompanied by loss of the D1 protein. This effect is dependent on the length of illumination, and the light intensity, and increased when carotenoid content was lowered during previous growth of the norflurazon-treated cultures.Abbreviations BSA
bovine serum albumin
- D1
32 kDa QB-binding protein
- EDTA
ethylenediaminetetraacetic acid
- LHCII
light-harvesting complex II
- PMSF
phenylmethylsulfonyl fluoride
- PS
photosystem
- tricine
N-[tris(hydroxymethyl)methyl] glycine 相似文献