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Biomedical subjects

S F Yang

Publications and source records attributed to S F Yang.

At least 73 records · Page 4Linked to original sources
PubMed1989

[Indications of cesarean section for severe heart diseases in pregnancy--an analysis of 61 cases].

Sixty-one cases of severe heart diseases were treated between Jan. 1977 and Dec. 1986, accounting for 18.37% of the heart diseases in pregnancy. Of these 61 cases, 39 (63.93%) underwent cesarean section under continuous lumbar epidural anesthesia. The systolic/diastolic blood pressure and mean arterial pressure (MAP) values decreased from the beginning of anesthesia to the end of delivery, and then the values gradually went up to the preoperative level. During the operation, no heart failure occurred. In 22 cases (36.07%), when labor began, the systolic/diastolic pressure and MAP increased and attained the peak value during parturition. After the fetus was delivered, the blood pressure decreased immediately. In 10 cases, heart failure occurred during labor. The adjusted mortality was 4.92%. Two patients died after vaginal delivery. Of these, one had heart failure during labor and underwent cesarean section, but she died after the operation. It was noted that hemodynamic change during cesarean section was smaller than that during vaginal delivery. If an appropriate time is selected for termination of pregnancy or cesarean section is only performed in the early stage of labor, heart failure and fatal outcome may be avoided.

Adult↗
PubMed1989

The interrelationship between the root surface and alveolar bone of the replanted avulsed tooth after etching.

It has been suggested that removal of the damaged nonvital periodontal ligament (PDL) may result in slower destruction of tooth substance following replantation of teeth. It has also been suggested that citric acid conditioning of surgically exposed dentin may enhance connective tissue attachment on root surfaces. The aim of this study was to examine the interrelationship between the acid etched root surface of the replanted tooth and the alveolar bone. Forty-five available anterior teeth from six monkeys were divided into 3 groups in this experiment. All teeth were extracted and dried for 2 hrs. In the first group the teeth were replanted immediately after endodontic therapy. The teeth in the second group were replanted after immersion in 10% sodium hypochlorite and subsequently irrigation with normal saline. In the third group, the cementum and necrotic PDL were removed by grinding the root surfaces which were then treated with citric acid (PH = 1) for 3 minutes followed by normal saline irrigation. All teeth were replanted without splinting and were subjected to histological examination at 12 week post-replantation. Close apposition of collagen fibrils of the new connective tissue to the exposed root surface was observed in most cases in the second and third group, although bony ankylosis and inflammatory root resorptions were also found in some areas. Teeth in the first group, the control experiment, had much more replacement and inflammatory resorptions. Then the result suggested that demineralization with citric acid on the denuded avulsed tooth prior to replantation may decrease the chance of replacement resorption and result in fibrous adhesion to the alveolar bone.

Adhesiveness↗
PubMed1988

S-adenosylmethionine-dependent inactivation and radiolabeling of 1-aminocyclopropane-1-carboxylate synthase isolated from tomato fruits.

1-Aminocyclopropane-1-carboxylic acid (ACC) synthase was partially purified from the homogenate of wounded tomato (Lycoperiscon esculentum Mill.) pericarp tissue by (NH(4))(2)SO(4) fractionation followed by conventional column chromatography with diethylaminoethyl-Sepharose, Sephadex G-150, Affi-Gel blue and hydroxylapatite. The partially purified ACC synthase preparation attained a specific activity of about 12,000 nmoles per hour per milligram protein. Employing this enzyme preparation, we confirmed that the ACC synthase was inactivated by its substrate, S-adenosyl-l-methionine (SAM), during its catalytic action. When the partially purified enzyme preparation was incubated with [3,4-(14)C]SAM and the resulting proteins were analyzed by sodium dodecyl sulfate-gel electrophoresis, only one radioactive protein band was observed. This protein was thought to be ACC synthase based on its molecular mass of 50 kD and on the fact that it was specifically bound to a monoclonal antibody against ACC synthase (AB Bleecker et al. 1986 Proc Natl Acad Sci USA 83, 7755-7759). These results suggest that the substrate SAM acts as an enzyme-activated inactivator of ACC synthase by covalently linking a fragment of SAM molecule to the active site of ACC synthase, resulting in the inactivation of the enzyme.

Journal Article↗
PubMed1988

Cyanide metabolism in relation to ethylene production in plant tissues.

HCN is the putative product of C-1 and amino moieties of 1-aminocyclopropane-1-carboxylic acid (ACC) during its conversion to ethylene. In apple (Malus sylvestrus Mill.) slices or auxin-treated mungbean (Vigna radiata L.) hypocotyls, which produced ethylene at high rates, the steady state concentration of HCN was found to be no higher than 0.2 micromolar, which was too low to inhibit respiration (reported Ki for HCN to inhibit respiration was 10-20 micromolar). However, these tissues became cyanogenic when treated with ACC, the precursor of ethylene, and with 2-aminoxyacetic acid, which inhibits beta-cyanoalanine synthase, the main enzyme to detoxify HCN; the HCN levels in these tissues went up to 1.7 and 8.1 micromolar, respectively. Although ethylene production by avocado (Persea gratissima) and apple fruits increased several hundred-fold during ripening, beta-cyanoalanine synthase activity increased only one- to two-fold. These findings support the notion that HCN is a co-product of ethylene biosynthesis and that the plant tissues possess ample capacity to detoxify HCN formed during ethylene biosynthesis so that the concentration of HCN in plant tissues is kept at a low level.

Journal Article↗
PubMed1988

Dependence of in vivo ethylene production rate on 1-aminocyclopropane-1-carboxylic Acid content and oxygen concentrations.

1-Aminocyclopropane-1-carboxylic acid (ACC) is aerobically oxidized in plant tissues to form ethylene by ethylene-forming enzyme (EFE). The effect of substrate (ACC and oxygen) concentrations on ethylene production rate by plant tissues was investigated. The K(m) value for O(2) in ethylene production varied greatly depending on the internal ACC content. When ACC levels in the tissue were low (below its K(m) value), the concentration of O(2) giving half-maximal ethylene production rate ([S](0.5)) ranged between 5 and 7%, and was similar among different tissues. As the concentration of ACC was increased (greater than its K(m) value), [S](0.5) for O(2) decreased markedly. In contrast, the K(m) value for ACC was not much dependent on O(2) concentration, but varied greatly among different plant tissues, ranging from 8 micromolar in apple (Malus sylvestris Mill.) tissue to 120 micromolar in etiolated wheat (Triticum aestivum) leaf. Such a great variation was thought to be due to the different compartmentation of ACC within the cells in different tissues. These kinetic data are consistent with the view that EFE follows an ordered binding mechanism in which EFE binds first to O(2) and then to ACC.

Journal Article↗
PubMed1988

Characterization of an Ethylene Overproducing Mutant of Tomato (Lycopersicon esculentum Mill. Cultivar VFN8).

Ethylene production rates and tissue ethylene concentrations were determined for the single-gene, Epinastic (Epi) tomato (Lycopersicon esculentum Mill.) mutant, and its parent, cv VFN8. The Epi phenotype was characterized by severe leaf epinasty, thickened stems and petioles, and a compact growth habit. In 4-day-old seedlings, ethylene production was significantly higher in Epi than in VFN8. Ethylene production rates also were higher for excised root, hypocotyl, cotyledon, and shoot tissue of 14-day-old Epi seedlings as compared with VFN8. The greatest difference in the ethylene production rate was observed in excised Epi shoot tissue, which was more than 2.5 times higher than in VFN8. Tissue ethylene concentrations of 19-, 25-, and 31-day-old Epi plants were 8, 172, and 307% higher than for VFN8, corresponding to increasing expression of the Epi phenotypic characteristics with age. The highest ethylene concentrations occurred in the shoot apex of both genotypes. Higher ethylene concentrations in Epi resulted from greater 1-aminocyclopropane-1-carboxylic acid content rather than increased ethylene-forming enzyme activity. The elevated ethylene levels in Epi did not result from increased auxin sensitivity. The sensitivity of root growth to inhibition by ethylene did not differ between VFN8 and Epi. Although elevated levels of ethylene in Epi plants apparently exacerbate its epinastic growth characteristics, other evidence indicates that this may not be the fundamental lesion. This mutant may provide a unique system for investigating the regulation of ethylene biosynthesis and the role of target cell types in plant development.

Journal Article↗
PubMed1987

Metabolism of 5-methylthioribose to methionine.

During ethylene biosynthesis, the H(3)CS- group of S-adenosylmethionine is released as 5'-methylthioadenosine, which is recycled to methionine via 5-methylthioribose (MTR). In mungbean hypocotyls and cell-free extracts of avocado, [(14)C]MTR was converted into labeled methionine via 2-keto-4-methylthiobutyric acid (KMB) and 2-hydroxy-4-methylthiobutyric acid (HMB), as intermediates. Incubation of [ribose-U-(14)C]MTR with avocado extract resulted in the production of [(14)C]formate, indicating the conversion of MTR to KMB involves a loss of formate, presumably from C-1 of MTR. Tracer studies showed that KMB was converted readily in vivo and in vitro to methionine, while HMB was converted much more slowly. The conversion of KMB to methionine by dialyzed avocado extract requires an amino donor. Among several potential donors examined, l-glutamine was the most efficient. Anaerobiosis inhibited only partially the oxidation of MTR to formate, KMB/HMB, and methionine by avocado extract. The role of O(2) in the conversion of MTR to methionine is discussed.

Journal Article↗
PubMed1987

The effect of light and phytochrome on 1-aminocyclopropane-1-carboxylic Acid metabolism in etiolated wheat seedling leaves.

While light-grown wheat leaves produced ethylene at a low rate of <0.1 nanomoles per gram per hour and contained 1-aminocyclopropane-1-carboxylic acid (ACC) at low levels of <2.5 nanomoles per gram, etiolated wheat leaves produced ethylene at a rate of 2 nanomoles per gram per hour and accumulated concentrations of ACC at levels of 40 nanomoles per gram. Upon illumination of 8-day-old etiolated wheat seedlings with white light, the ethylene production rate increased initially, due to the activation of ethylene-forming activity, but subsequently declined to a low level (0.1 nanomoles per gram per hour) at the end of the 6-hour illumination. This light-induced decline in ethylene production rate resulted from a decline (more than 35 nanomoles per gram) in ACC level, which was accompanied by a corresponding increase in 1-(malonylamino)cyclopropane-1-carboxylic acid content. These data indicate that illumination promoted ACC malonylation, resulting in reduced ACC level and consequently reduced ethylene production. However, light did not cause any significant increase in the extractable ACC-malonyltransferase activity. The effect of continuous white light on promotion of ACC malonylation was also observed in intermittent white light or red light. A far-red light treatment following red light partially reversed the red light effect, indicating that phytochrome participates in the promotion of ACC malonylation.

Journal Article↗
PubMed1986

Effect of thidiazuron, a cytokinin-active urea derivative, in cytokinin-dependent ethylene production systems.

Cytokinins are known to stimulate ethylene production in mungbean hypocotyls synergistically with indoleacetic acid (IAA), in mungbean hypocotyls synergistically with Ca(2+), and in wilted wheat leaves. Thidiazuron, a substituted urea compound, mimicked the effect of benzyladenine (BA) in all three systems. In the Ca(2+) + cytokinin system and the IAA + cytokinin systems of mungbean hypocotyls, thiadiazuron was slightly more active than BA at equimolar concentration. In mungbean hypocotyls exogenously applied IAA was rapidly conjugated into IAA asparate, and this conjugation process was effectively inhibited by thidiazuron, as by cytokinins. In the wilted wheat leaves system, 10 micromolar thidiazuron exerted stress ethylene production equal to that exerted by 1 millimolar BA, indicating that thidiazuron is more active than BA by two orders. The structure-activity relationship of thidiazuron and its thiadiazolylurea analogs in stimulating Ca(2+)-dependent ethylene production in mungbean hypocotyls was found to agree well with the structure-activity relationship of these derivatives in promoting the growth of callus tissues. These results indicate that thidiazuron and its derivatives are highly active to mimic the adenine-type cytokinin responses in promoting ethylene production and that the structure-activity relationship in promoting the growth of callus and in promoting ethylene production is similar.

Journal Article↗
PubMed1986

Interferences and specificity of the 1-aminocyclopropane-1-carboxylic Acid assay with the hypochlorite reagent.

1-Aminocyclopropane-1-carboxylic Acid (ACC), the immediate precursor of ethylene is routinely assayed by converting it into ethylene with NaOCl, and the ethylene liberated is then determined by gas chromatography (MCC Lizada, SF Yang 1979 Anal Biochem 100: 140-145). However, certain materials which may be present in crude plant extracts or in enzyme reaction mixtures interfere with this assay procedure. Mono, and di-alkyl amines cause poor yields of ethylene from ACC. Ethanol in the presence of NH(3) or amines but in the absence of ACC can produce ethylene under the assay procedure. The characteristics of these interfering reactions were studied and precautions to avoid these problems are suggested. Recovery of ACC during its extraction and purification from plant extracts were tested and are discussed.

Journal Article↗
PubMed1986

The Conversion of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid to 1-Aminocyclopropane-1-Carboxylic Acid in Plant Tissues.

Since 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), the major conjugate of 1-aminocyclopropane-1-carboxylic acid (ACC) in plant tissues, is a poor ethylene producer, it is generally thought that MACC is a biologically inactive end product of ACC. In the present study we have shown that the capability of watercress (Nasturtium officinale R. Br) stem sections and tobacco (Nicotiana tabacum L.) leaf discs to convert exogenously applied MACC to ACC increased with increasing MACC concentrations (0.2-5 millimolar) and duration (4-48 hours) of the treatment. The MACC-induced ethylene production was inhibited by CoCl(2) but not by aminoethoxyvinylglycin, suggesting that the ACC formed is derived from the MACC applied, and not from the methionine pathway. This was further confirmed by the observation that radioactive MACC released radioactive ACC and ethylene. A cell-free extract, which catalyzes the conversion of MACC to ACC, was prepared from watercress stems which were preincubated with 1 millimolar MACC for 24 hours. Neither fresh tissues nor aged tissues incubated without external MACC exhibited enzymic activity, confirming the view that the enzyme is induced by MACC. The enzyme had a K(m) of 0.45 millimolar for MACC and showed maximal activity at pH 8.0 in the presence of 1 millimolar MnSO(4). The present study indicates that high MACC levels in the plant tissue can induce to some extent the capability to convert MACC to ACC.

Journal Article↗
PubMed1986

The induction of ethylene production from pear cell culture by cell wall fragments.

Macerase, a pectinase-containing enzyme mixture, was used to digest cell walls isolated from cultured pear cells. Following digestion, the reaction mixture was boiled to inactivate enzymes. Addition of soluble aliquots of the mixture to suspension cultures of pear cells led to a rapid and transient production of ethylene by the cells.

Journal Article↗
PubMed1986

Carbon dioxide enhances the development of the ethylene forming enzyme in tobacco leaf discs.

Since CO(2) is known to stimulate ethylene production by promoting the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene, the effect of CO(2) on the activity and the development of the ethylene forming enzyme (EFE) was studied in tobacco (Nicotiana tabacum L. cv Havana 425 and Xanthi) leaf discs. In addition to previous observations that EFE activity is dependent on CO(2) concentration and is saturable with 2% CO(2), present data show two saturation curves at 2% and 10% CO(2). Promotion of EFE development was dependent also on CO(2) concentration (saturated at 2% CO(2)) and duration (maximum at 24 in the dark), and was abolished by 20 micromolar cycloheximide. Application of exogenous ethylene (20 microliters per liter) or light treatment further increased the CO(2)-enhanced development of EFE, implying that these two factors can also affect EFE development via interaction with CO(2). The results suggest that CO(2) exerts its stimulatory effect on the conversion of ACC to ethylene by enhancing not only the activity but also the synthesis of EFE in leaf discs.

Journal Article↗