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651.
The functional properties of the transport of lysine across the chicken erythrocyte membrane were investigated. The animal
population studied (male Leghorn chickens, 6–14 weeks old) was found to consist of two groups presenting either low (LT, 19
individuals) or high transport rates (HT, 20 individuals). The rates of influx in the two groups, measured at a concentration
of l-lysine of 1 μm, differed by a factor of 34. The transport activities observed in LT and HT erythrocytes were compatible with the general
features of system y+L, but showed some differences in specificity. The transporter in the LT group was found to bind l-lysine, l-leucine, l-methionine and l-glutamine with high affinity, in the presence of sodium, as described for system y+L in human erythrocytes. The activity present in HT erythrocytes exhibited a much lower affinity for l-leucine, but was able to interact strongly with l-glutamine and l-methionine. The specificity pattern of the HT transporter, has not been described in other cell types. In other respects,
the properties of the two systems were similar. Sodium replacement with potassium, drastically reduced the affinity for l-leucine, without affecting lysine transport. Both transporters function as tightly coupled exchangers, are inactivated by
p-chloromercuribenzene sulfonate and resistant to N-ethylmaleimide. These findings explain previous results obtained in selective
breeding experiments of chicken with high and low amino-acid transport activity.
Received: 12 February 2001/Revised: 11 June 2001 相似文献
652.
Synaptosomes isolated from adult or newborn rat cerebrum take up l-lysine by two saturable systems, one with a high affinity low capacity and the other with a low affinity high capacity. Initial rate of uptake for low lysine concentrations is more rapid in newborn, but for high concentrations the rate is greater in adult tissue. Analysis of kinetic data indicates that synaptosomes of the newborn have a higher than those of the adult for high affinity system but adult synaptosomes have a higher than newborn for low affinity system. At a physiological lysine concentration of 0.5 mM, the calculated contributions of two systems indicate that the adult uptake occurs for about 71% by low affinity system but the newborn utilizes both systems to the same extent. The uptake is sodium independent but pH dependent. Lysine uptake is inhibited by other dibasic amino acids, arginine and ornithine but not cystine. Kinetic analysis indicates that arginine specifically inhibits the high affinity, low system for lysine uptake. 相似文献
653.
《Biochemical and biophysical research communications》2020,521(1):19-23
BackgroundThe post-translational protein modification via lysine residues can significantly alter its function. α2-antiplasmin, a key inhibitor of fibrinolysis, contains 19 lysine residues.AimWe sought to identify sites of glycation and acetylation in human α2-antiplasmin and test whether the competition might occur on the lysine residues of α2-antiplasmin.MethodsWe analyzed human α2-antiplasmin (1) untreated; (2) incubated with increasing concentrations of β-d-glucose (0, 5, 10, 50 mM); (3) incubated with 1.6 mM acetylsalicylic acid (ASA) and (4) incubated with 1.6 mM ASA and 50 mM β-d-glucose, using the ultraperformance liquid chromatography system coupled to mass spectrometer.ResultsEleven glycation sites and 10 acetylation sites were found in α2-antiplasmin. Incubation with β-d-glucose was associated with glycation of 4 (K-418, K-427, K-434, K-441) out of 6 lysine residues, known to be important for mediating the interaction with plasmin. Glycation and acetylation overlapped at 9 sites in samples incubated with β-d-glucose or ASA. Incubation with concomitant ASA and β-d-glucose was associated with the decreased acetylation at all sites overlapping with glycation sites. At K-182 and K-448, decreased acetylation was associated with increased glycation when compared with α2-antiplasmin incubated with 50 mM β-d-glucose alone. Although K-24 located in the proximity of the α2-antiplasmin cleavage site, was found to be only acetylated, incubation with ASA and 50 mM β-d-glucose was associated the absence of acetylation at that site.ConclusionHuman α2-antiplasmin is glycated and acetylated at several sites, with the possible competition between acetylation and glycation at K-182 and K-448. Our finding suggests possibly relevant alterations to α2-antiplasmin function at high glycemia and during aspirin use. 相似文献
654.
High performance liquid chromatography (HPLC) followed by radioimmunoassay (RIA) of the chromatographic fractions were used to separate and quantify, respectively, the alpha MSH-like peptides stored in the neurointermediate lobe (NIL) of the Xenopus laevis (X. laevis) pituitary gland and released from the X. laevis NIL, in vitro. Immunoreactive (IR) material eluting with a similar HPLC retention time as desacetyl alpha MSH was the major IR peptide in the NIL. Material with a retention time similar to alpha MSH and immunological properties equivalent to alpha MSH was also present in the NIL. However, the retention times of the X. laevis and mammalian alpha MSH-like peptides were not identical, suggesting species difference in these peptides. Following incubation of NILs in the presence of [3H]-acetyl CoA, the X. laevis variant of alpha MSH was the major [3H]-labeled, immunoprecipitable material present. Following an incubation of NILs in the presence of [3H]-amino acids for 21 hours, immunoprecipitable [3H]-alpha MSH was detected in the NILs and the ratio of [3H]-desacetyl alpha MSH to [3H]-alpha MSH was similar to the ratio of IR-desacetyl alpha MSH to IR-alpha MSH. The X. laevis variant of alpha MSH was the major alpha MSH-like peptide released from the NILs into the incubation medium. Dopamine (50 microM) significantly inhibited the release of IR-alpha MSH but not IR-desacetyl alpha MSH. No net increase in total alpha MSH (sum of release and NIL content) was observed in the actively secreting (control) NIL group versus the dopamine-treated group. These results indicate that acetylation of desacetyl alpha MSH occurs intracellularly. 相似文献
655.
I. Negrutiu A. Cattoir-Reynearts I. Verbruggen M. Jacobs 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1984,68(1-2):11-20
Summary Two S-(2-aminoethyl)L-cysteine (AEC) resistant lines were isolated by screening mutagenized protoplasts from diploid N. sylvestris plants. Both lines accumulated free lysine at levels 10 to 20-fold higher than in controls. Lysine overproduction and AEC-resistance were also expressed in plants regenerated from the variant cultures. A feedback insensitive form of dihydrodipicolinate synthase (DHPS), the pathway specific control enzyme for lysine synthesis, was detected in callus cultures and leaf extracts from the resistant lines. Aspartate kinase (AK), the other key enzyme in the regulation of lysine biosynthesis, was unaltered in the mutants. Crosses with wild type plants indicated that the mutation conferring insensitivity to feedback in DHPS, with as result overproduction of lysine and resistance to AEC, was inherited as a single dominant nuclear gene.Abbreviations AK
aspartate kinase (EC 2.7.2.4)
- DHPS
dihydrodipicolinate synthase (EC 4.2.1.52)
- AEC
S-(2-aminoethyl)L-cysteine 相似文献
656.
Abstract: Cationic amino acids are transported from blood into brain by a saturable carrier at the blood-brain barrier (BBB). The transport properties of this carrier were examined in the rat using an in situ brain perfusion technique. Influx into brain via this system was found to be sodium independent and followed Michaelis-Men-ten kinetics with half-saturation constants (Km ) of 50–100 μM and maximal transport rates of 22–26 nmol/min/g for L-lysine, L-arginine, and L-ornithine. The kinetic properties matched that of System y+ , the sodium-independent cationic amino acid transporter, the cDNA for which has been cloned from the mouse. To determine if the cloned receptor is expressed at the BBB, we assayed RNA from rat cerebral microvessels and choroid plexus for the presence of the cloned transporter mRNA by RNase protection. The mRNA was present in both cerebral microvessels and choroid plexus and was enriched in microvessels 38-fold as compared with whole brain. The results indicate that System y+ is present at the BBB and that its mRNA is more densely expressed at cerebral microvessels than in whole brain. 相似文献
657.
《Journal of molecular biology》2023,435(5):167968
Type I interferons (IFN) are cytokines that bridge the innate and adaptive immune response, and thus play central roles in human health, including vaccine efficacy, immune response to cancer and pathogen infection, and autoimmune disorders. Post-translational protein modifications by the small ubiquitin-like modifiers (SUMO) have recently emerged as an important regulator of type I IFN expression as shown by studies using murine and cellular models and recent human clinical trials. However, the mechanism regarding how SUMOylation regulates type I IFN expression remains poorly understood. In this study, we show that SUMOylation inhibition does not activate IFNB1 gene promoter that is regulated by known canonical pathways including cytosolic DNA. Instead, we identified a binding site for the chromatin modification enzyme, the SET Domain Bifurcated Histone Lysine Methyltransferase 1 (SETDB1), located between the IFNB1 promoter and a previously identified enhancer. We found that SETDB1 regulates IFNB1 expression and SUMOylation of SETDB1 is required for its binding and enhancing the H3K9me3 heterochromatin signal in this region. Heterochromatin, a tightly packed form of DNA, has been documented to suppress gene expression through suppressing enhancer function. Taken together, our study identified a novel mechanism of regulation of type I IFN expression, at least in part, through SUMOylation of a chromatin modification enzyme. 相似文献