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F Xu

Publications and source records attributed to F Xu.

18 recordsLinked to original sources
PubMed1992

Characterization of NADPH-dependent methemoglobin reductase as a heme-binding protein present in erythrocytes and liver.

An NADPH-dependent reductase, first shown in the 1930s to catalyze the methylene blue-dependent reduction of methemoglobin in erythrocytes, has now been characterized as a high-affinity heme-binding protein and has been detected in liver. Highly purified bovine erythrocyte reductase binds protohemin to form a 1:1 complex with a Kd of 7 nM. Binding of protohemin completely inhibits reductase activity. Other tetrapyrroles and fatty acids also bind to the reductase and inhibit its activity. Protoporphyrin, hematoporphyrin, and coproporphyrin form 1:1 complexes with Kd values ranging from 1 to 5 microM. The inhibition constants for a number of saturated and unsaturated fatty acids range from 6 to 52 microM. A protein that is immunologically cross-reactive to the reductase has been detected in the cytosolic fractions of bovine and rat liver and of bovine, rat, rabbit, and human erythrocytes. By immunoblot analysis, the bovine liver and erythrocyte proteins appear identical in size, as do the rat liver and erythrocyte proteins. The concentration of the protein in bovine erythrocytes has been estimated by quantitative immunoblotting to be 10 microM. The detection of this protein in liver cells, the demonstration of its binding properties, and its weak reductase activity bring into question the long-held belief that this is uniquely an erythrocyte protein and that it functions as a reductase.

Animals↗
PubMed1992

Topography of cat medullary ventral surface hypoxic acidification.

The topographic relationship between previously identified medullary ventral surface respiratory chemosensitive regions and brain surface extracellular fluid (ECF) acid production during acute hypoxia was explored in anesthetized, paralyzed, and artificially ventilated cats. Glass pH electrodes (0.8-mm diam, sheathed in stainless steel tubing) were mounted in mechanical contact with surfaces of medullary surface or adjacent pyramids, pons, spinal cord, or parietal cortex. Isocapnic hypoxia of 5 min [at arterial O2 saturation (SaO2) = 48 +/- 10%] reduced pH over rostral (Mitchell) and caudal (Loeschcke) areas by 0.12 +/- 0.09 and 0.07 +/- 0.04, respectively (n = 10, P < 0.05). Change in pH (delta pH) was proportional to desaturation with slopes 100 delta pH/delta SaO2 of 0.45 (rostral) and 0.20 (caudal) (R = 0.91 and 0.88, respectively). pH drop usually began within 3 min of hypoxia, became stable between 5 and 15 min, began to rise within 2 min of reoxygenation, and returned to control within 10 min. During equally hypoxic tests, intermediate area (Schläfke), pons, and spinal cord surfaces showed no significant acid shift. Parietal cortex ECF pH dropped more slowly but steadily by 0.079 +/- 0.034 during 20 min at SaO2 = 50% after a small but significant initial alkaline shift, and acidification of cortical surface continued for > 5 min after reoxygenation. We conclude that medullary ventral chemosensitive regions produce more lactic acid during hypoxia than neighboring brain surfaces.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Study of early hematopoietic precursors in human cord blood.

Human cord blood is a source of transplantable stem cells. These stem cells express the antigen CD34, are resistant to treatment with 4-hydroperoxycyclophosphamide (CD34+/4-HCres), and do not give rise to colonies when plated in clonogenic assays. We studied the number of CD34+ cells present in cord blood and developed a two-step assay for early precursors (pre-colony-forming units, pre-CFU) capable of giving rise to committed progenitors. In this assay CD34+/4-HCres cord blood cells were cultured in suspension with different growth factors. After 7 days in suspension the remaining cells were plated in clonogenic assays, for granulocyte-macrophage colony-forming units (CFU-GM), erythroid burst-forming units (BFU-E), and mixed lineage colony-forming units (CFU-MIX), in the presence of pure factors or a combination of recombinant human (rh) interleukin 3 (IL-3) and medium conditioned by the PU34 primate cell line. Pre-CFU for all precursors were identified. These pre-CFU developed into committed progenitors in response to rhIL-3. The combinations of rhIL-3 plus rh interleukin 1 (IL-1) or rhIL-3 plus rh interleukin 6 (IL-6) did not enhance recovery of progenitors. The developing CFU-GM were responsive to rh granulocyte-macrophage colony-stimulating factor (GM-CSF) and rh granulocyte colony-stimulating factor (G-CSF) but much less so to rhIL-3. BFU-E and CFU-MIX developed in suspension but could only be detected when cells were replated in the presence of a combination of rhIL-3 and PU34 but not rhIL-3 alone. This assay may be useful in evaluating the number of early hematopoietic precursors present in cord blood samples and in defining growth factor combinations that could enhance hematopoietic recovery after cord blood stem cell transplants.

Antigens, CD↗
PubMed1992

Effects of radiation and 4-hydroperoxycyclophosphamide on production of G- and GM-CSF by stromal cells.

The effects of in vitro radiation and exposure to 4-hydroperoxycyclophosphamide (4-HC) on the production of G- and GM-CSF by different components of the human hematopoietic microenvironment are described. The marrow microenvironment is composed of fibroblasts, endothelial cells, macrophages, and adipocytes. To study the effects of radiation/4-HC on colony-stimulating factor (CSF) production by stromal cells, confluent layers of umbilical cord endothelial cells (EC), marrow fibroblasts (MF), and heterogeneous adherent layers (HAL) derived from long-term marrow cultures were established. These layers were exposed to radiation up to 3000 cGy and/or 100 mumol/ml of 4-HC and subsequently stimulated with IL-1 beta on day 0, 7, or 14 after radiation/4-HC. Following IL-1 exposure conditioned medium (CM) was collected and G- and GM-CSF levels were measured by ELISA and their ability to support colony formation was assessed. G- and GM-CSF levels after exposure to 4-HC and radiation were 12,460 +/- 172 pg/ml and 2268 +/- 160 pg/ml for EC, 2214 +/- 94 pg/ml and 263 +/- pg/ml for MF, and 3168 +/- 316 pg/ml and 356 +/- 34 pg/ml for HALs, respectively. For each cell group there was no significant difference between levels obtained without exposure and levels after exposure to 4-HC and/or radiation (p > 0.6). Comparison of levels obtained from different cell groups showed significant differences with EC media being the highest (p < 0.0001). To test the activity of these measured factors, CM of different sources was used in colony assays of CD 34+ cord blood progenitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Marrow↗
PubMed1992

[Hurler syndrome (a case report)].

A case of Hurler syndrome diagnosed by clinical and laboratory examination is reported. The patient's roentgenograms showed the dystrophies of bones, lace-shaped ribs, boat-shaped cranium, fishhook-shaped forefront protrusion of silla trucica. Corneal opacities and high ocular pressure were found in both eyes. VEP measurement suggested the defects of optic nerve. The authors emphasized that visual electric physiological examinations should be used to estimate the visual functions when the patient's refractive medium is opqaue. The differential diagnosis was also briefly discussed.

Child↗
PubMed1992

[Analysis of the linear migration of the radionuclide along meridians in perfused extremities of monkey].

On the basis of researches in human body, further experiment in monkeys was conducted and the result has demonstrated that: 1. There was a close and complicated relation between the migration of 99mTc injected into acupoints and the blood circulation. 2. The location of the migration was mainly in the subcutaneous lay. 3. There were no direct relationship between the migration and periphery nerve system.

Animals↗
PubMed1992

[The role of ear electroacupuncture on arterial pressure and respiration during asphyxia in rabbits].

This paper reports the study of the effect of ear electroacupuncture (EA) inserted in the "Er Jian" point on arterial pressure and integrated phrenic nerve discharge (IPND). The result showed that the arterial pressure was decreased and frequency of IPND was increased. The differences as follows: During spontaneous breathing, the blood pressure and IPND were -36.56 +/- 26.63 mmHg and, 2.42 +/- 1.42 spikes/10S (P less than 0.001); in excitatory period, -24.31 +/- 6.01 mmHg and, 2.16 +/- 1.12 spikes/10S (P less than 0.01) and in inhibitory period -18.26 +/- 7.04 mmHg (P less than 0.01) and, 2.07 +/- 1.07 spikes/10S (P less than 0.05). The lasting time was 26 min, 330S and 280S. We observed 20 cases with hypertension by ear electro-acupuncture. The systolic pressure and diastolic pressure of hypertension patients were decreased (P less than 0.001) and respiratory rate increased (P less than 0.05).

Acupuncture Points↗
PubMed1992

[The use of 6-flavor Rehmannia decoction with additives in the prevention of ototoxic deafness induced by gentamicin in guinea pigs].

The purpose of this study is to discuss the effects of the Chinese medicine six-flavor Rehmannia Decoction with additives on preventing deafness induced by gentamicin (GM) in guinea pig by means of testing the thresholds of Preyer's reflex (PR) cochlear microphonic potential (CM), action potential of the auditory nerve (N1) and scanning electron microscope of inner ear (SEM). The results showed that the medicine is effective in reducing the ototoxic effect of GM on inner ear.

Action Potentials↗
PubMed1992

Bovine erythrocyte glutathione S-transferase: purification, inhibition, and complex formation.

Glutathione S-transferase has been purified from bovine erythrocytes by affinity chromatography. The enzyme has an isoelectric point of 7.2, behaves as a 48-kDa protein composed of two identical subunits, and has an N-terminal sequence of PPYTIVYFPVQGR?EAMRMLL. This sequence, the amino acid composition, and the kinetic parameters suggest that the enzyme belongs to the pi-class of transferases. Hemins, porphyrins, and fatty acids form complexes with the enzyme and serve as effective inhibitors. Treatment of the transferase with N-ethylmaleimide, 3-amino-1,2,4-triazole, diethyl pyrocarbonate, or 2,3-butanedione inhibits transferase activity without altering tetrapyrrole binding. The role of the complexation and inhibition of glutathione S-transferase in erythroid metabolism has yet to be elucidated.

Amino Acid Sequence↗
PubMed1992

Overregularization in language acquisition.

Children extend regular grammatical patterns to irregular words, resulting in overregularizations like comed, often after a period of correct performance ("U-shaped development"). The errors seem paradigmatic of rule use, hence bear on central issues in the psychology of rules: how creative rule application interacts with memorized exceptions in development, how overgeneral rules are unlearned in the absence of parental feedback, and whether cognitive processes involve explicit rules or parallel distributed processing (connectionist) networks. We remedy the lack of quantitative data on overregularization by analyzing 11,521 irregular past tense utterances in the spontaneous speech of 83 children. Our findings are as follows. (1) Overregularization errors are relatively rare (median 2.5% of irregular past tense forms), suggesting that there is no qualitative defect in children's grammars that must be unlearned. (2) Overregularization occurs at a roughly constant low rate from the 2s into the school-age years, affecting most irregular verbs. (3) Although overregularization errors never predominate, one aspect of their purported U-shaped development was confirmed quantitatively: an extended period of correct performance precedes the first error. (4) Overregularization does not correlate with increases in the number or proportion of regular verbs in parental speech, children's speech, or children's vocabularies. Thus, the traditional account in which memory operates before rules cannot be replaced by a connectionist alternative in which a single network displays rotelike or rulelike behavior in response to changes in input statistics. (5) Overregularizations first appear when children begin to mark regular verbs for tense reliably (i.e., when they stop saying Yesterday I walk). (6) The more often a parent uses an irregular form, the less often the child overregularizes it. (7) Verbs are protected from overregularization by similar-sounding irregulars, but they are not attracted to overregularization by similar-sounding regulars, suggesting that irregular patterns are stored in an associative memory with connectionist properties, but that regulars are not. We propose a simple explanation. Children, like adults, mark tense using memory (for irregulars) and an affixation rule that can generate a regular past tense form for any verb. Retrieval of an irregular blocks the rule, but children's memory traces are not strong enough to guarantee perfect retrieval. When retrieval fails, the rule is applied, and overregularization results.

Age Factors↗
PubMed1992

[DNA repair capacity measurement and possibility of heterozygote detection using nucleoid sedimentation technique among members taken from 3 xeroderma pigmentosum (XP) families].

The nucleoid sedimentation test was used to analyse the DNA repair capacity in 35 members taken from 3 xeroderma pigmentosum (XP) families after their peripheral blood lymphocytes being exposed to UV irradiation or N-methyl-N-nitro-N-nitrosoguanidine (MNNG) at a dose of 2.5 microJ/mm2 and 2 micrograms/ml respectively. The results showed that the 6 XP patients all failed to repair their damaged DNA even after 20-hour incubation at 37 degrees C. The repair ratios were 0.61 +/- 0.13 for UV and 0.44 +/- 0.15 for MNNG while those of non-related normal members usually reached 0.96 +/- 0.07 and 0.71 +/- 0.07 for both UV and MNNG after 11-hour incubation. It is interesting to note that 9 obligatory heterozygotes (parents and grandparents of XP patients) and 4 highly possible heterozygotes (blood relatives of XP patients) also showed very poor DNA repair capacity: they could not accomplish their repair process even after 20-hour incubation. It has been showed that the nucleoid sedimentation test can probably be used to pick out the heterozygotes in XP families.

Adolescent↗
PubMed1991

Coupling of dihydroriboflavin oxidation to the formation of the higher valence states of hemeproteins.

The reactions between hydrogen peroxide and hemeproteins have been coupled to the oxidation of dihydroriboflavin so as to provide a simple method for measuring the rate constant of hemeprotein peroxidation. Dihydroriboflavin rapidly reduces the higher oxidation states of iron and the hydroxy radicals which are the products of the hemeprotein/hydrogen peroxide reaction. The rapid reduction of these highly reactive compounds prevents the hemeproteins from undergoing irreversible chemical modifications and thus allows the kinetics of peroxidation to be studied. The rate constants at pH 7.2 and 23 degrees C for the peroxidation of horseradish peroxidase, myoglobin, and ferrocytochrome c are found to be 6.2 x 10(6), 7.5 x 10(4), and 8 x 10(3)M-1s-1, respectively. These studies suggest that reduced riboflavin might efficiently protect cells from oxidative damage such as that occurring in inflammation and reperfusion injury.

Animals↗
PubMed1991

Evidence that the protein components of bovine erythrocyte green heme binding protein and flavin reductase are identical.

Bovine erythrocyte green heme binding protein and bovine erythrocyte flavin reductase have been isolated in highly purified forms and subjected to amino acid analysis and N-terminal amino acid sequence analysis. The two proteins possess similar amino acid compositions and identical N-terminal amino acid sequences. Moreover, the two proteins are immunochemically cross-reactive and are indistinguishable when compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by double diffusion technique. This study provides evidence that the protein components of bovine erythrocyte green heme binding protein and flavin reductase are identical.

Amino Acid Sequence↗
PubMed1990

[Study on forecasting local rubella outbreaks in Hangzhou city proper by serologic method].

Rubella outbreaks were proved by the rubazyme M test (Abbott) and rubella haemagglutination inhibition test in Hangzhou city in 1987. On the basis of these and previous immune surveillance in human population, we predict that epidemic of rubella will also occur in recent two years. Rubella IgM antibody was detected by enzyme immunoassay using commercially available Rubazyme-M Diagnostic Kit (Abbott Laboratories). It was detected within 0-66 days after eruption and detection rate was the highest between 5th and 14th day of onset. The coincidence rate of enzyme immunoassay and HAI tests for rubella diagnosis was 90.3%, and false negative rate of enzyme immunoassay was 9.7%. Besides, the importance of differentiating measles from rubella and diagnostic criteria of HAI test for rubella were discussed.

China↗
PubMed1990

[Studies on sensor for L-ascorbic acid using biotissue slice].

Bioselective membrane electrode for L-ascorbic acid has been made with tissue slices. It is made from porcine liver tissue slice covering an oxygen electrode. The influence of buffer mediator, pH, temperature, antiseptics, slice thickness, etc. on the response characteristics of the electrode was examined. In the presence of copper ions, a linear relationship between dynamic response of the electrode and the logarithm of concentration of L-ascorbic acid was observed for the range of 21.14 micrograms/ml to 352.3 micrograms/ml, with a correlation coefficient of 0.9996 and the Michaelis constant of 0.8 mmol/L. The electrode has been used to determine L-ascorbic acid in drugs, the analytical results were satisfactory.

Animals↗