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Z Y Sun

Publications and source records attributed to Z Y Sun.

36 records · Page 2Linked to original sources
PubMed1996

A site-directed mutagenesis of pro-urokinase which substantially reduces its intrinsic activity.

Single-chain urokinase-type plasminogen activator or pro-urokinase is a zymogen with an intrinsic catalytic activity which is greater than that of most other zymogens. To study the structural basis for this activity, a three-dimensional homology model was calculated using the crystallographic structure of chymotrypsinogen, and the structure-function relationship was studied using site-directed mutagenesis and kinetic analysis. This model revealed a unique Lys300 in pro-urokinase which could form a weak interaction with Asp355, adjacent to the active site Ser356. It was postulated that this lysine, by its epsilon-amino group, may serve to pull Ser356 close to the active position, thereby inducing the higher intrinsic activity of pro-urokinase. This was consistent with the published finding that a homologous lysine (Lys416) in single chain tissue plasminogen activator when mutated to serine induced some reduction in activity. To test this hypothesis, a site-directed mutant with a neutral residue (Lys300-->Ala) was produced and characterized. The Ala300-pro-urokinase had a 40-fold lower amidolytic activity than that of pro-urokinase. It was also stable in plasma at much higher concentrations than pro-urokinase, reflecting much attenuated plasminogen activation. Plasmin activatability was comparable to that of pro-urokinase, but the resultant two-chain derivative (Ala300-urokinase) had a lower enzymatic activity (approximately 33% that of urokinase) due to a reduction of kcat. Interestingly, the KM of two-chain Ala300-urokinase against plasminogen was 5.8-fold lower than that of urokinase, being similar to that of pro-urokinase which has a KM about 5-fold lower than urokinase. In conclusion, the hypothesis that Lys300 is a key structural determinant of the high intrinsic activity of pro-urokinase was confirmed by these studies. This residue also appears to be important for the full expression of the enzymatic activity of urokinase.

Enzyme Activation↗
PubMed1996

Tetanic stimulation and cyclic adenosine monophosphate regulate segregation of presynaptic inputs on a common postsynaptic target neuron in vitro.

Previous studies indicated that Aplysia sensory neurons (SNs) compete when reestablishing synapses with a motor cell target (L7) in vitro. The competition is characterized by a cell number-dependent decrease in the efficacy of each connection, an increase in the elimination of SN varicosities, a reduction in the formation of new SN varicosities, and the segregation of varicosities of each SN to restricted portions of the target axons. The changes do not require spike activity, since both the SNs and L7 do not fire spontaneously. Here, we examined whether adding activity to SNs during the early stages of synapse formation with stimuli known to evoke facilitatory responses in stable SN-L7 connections--tetanic stimulation or increase in intracellular cyclic adenosine monophosphate (cAMP)--would modulate the intrinsic segregatory process. Tetanic stimulation to one SN increased synapse efficacy and the number of varicosities of the stimulated SNs while reducing the functional changes by the nonstimulated SNs in the same cultures. An increase in the stability of preexisting varicosities contributed to the overall increase in varicosities evoked by tetanus. The functional changes evoked by tetanus were not expressed when the same tetanic stimulation was also given to the other SN, or when L7 was hyperpolarized during the tetanus to the SN. Raising cAMP levels in one SN increased synapse efficacy and the rate of new varicosity formation by the injected SNs without affecting the development of the connections formed by the noninjected SNs. These results suggest that different forms of presynaptic and postsynaptic activities in neurons can regulate specific aspects of the competitive process associated with the fine-tuning of connections formed by converging presynaptic inputs.

Animals↗
PubMed1996

Development of short-term heterosynaptic facilitation at aplysia sensorimotor synapses in vitro is accompanied by changes in the functional expression of presynaptic serotonin receptors.

1. The sensorimotor synapse of Aplysia expresses various shortlasting changes in synaptic efficacy including homosynaptic depression (HSD) and heterosynaptic facilitation by serotonin (5-HT) either at nondepressed sensory neuron (SN) synaptic connections or at SN synaptic connections first depressed by HSD. We examined the temporal sequence of expression for these three forms of synaptic plasticity as synaptic connections between SN and target motor cell L7 were reestablished and stabilized in cell culture. The same cultures were reexamined at different time points. 2. We found that only HSD and facilitation of nondepressed synapses were expressed at "mature" levels on day 1 in culture, whereas facilitation of depressed connections was significantly weaker on day 1 than the facilitation evoked on day 4. 3. The late expression of 5-HT facilitation of depressed SN synaptic connections was not a result of a reduced capacity of two kinases activated by 5-HT (protein kinase A and protein kinase C) to evoke facilitation. Direct activation of the kinases with either cyclic AMP or phorbol esters evoked the synaptic facilitation both on day 1 and day 4. 4. The late expression of 5-HT facilitation of depressed SN synaptic connections was correlated with the late functional expression of receptors sensitive to 5-HT antagonists cyproheptidine or methiothepin. Both antagonists significantly interfered with 5-HT facilitation on day 4, but both had little effect on 5-HT facilitation of the same cultures examined on day 1. 5. Unlike the properties of SNs in the intact nervous system, both antagonists reduced significantly the excitability changes evoked by 5-HT when the SNs were plated either alone or with target cell L11 that fails to induce synapse formation. When cultured with L7, however, both antagonists evoked little change in 5-HT excitability. In the presence of L7, the SNs expressed the phenotype more typical of SNs in the intact nervous system. 6. The results suggest that target interactions not only influence the formation of chemical connections but they also may regulate the acquisition of specific plastic properties by the presynaptic neuron including the functional expression of receptors for neuromodulators.

Animals↗
PubMed1995

Stopped-flow kinetic and biophysical studies of membrane-associated D-lactate dehydrogenase of Escherichia coli.

The enzyme kinetics of the FAD-containing membrane-associated D-lactate dehydrogenase (D-LDH) of Escherichia coli have been investigated by stopped-flow spectroscopy. The reduction of D-LDH by the substrate, D-lactate, exhibits a two-stage behavior as observed by the absorbance change for the enzyme-bound FAD. The fast stage with a maximum rate of 400 s-1 represents the rapid formation of the enzyme-substrate complex and the formation of the equilibrium between the oxidized and the reduced enzyme-substrate complexes. The slow stage, which occurs on the order of 0.36 s-1, represents the slow release of the product, pyruvate, from the reduced enzyme. The formation of a D-LDH semiquinone radical was not observed during the oxidation of D-lactate by D-LDH at 25 degrees C. However, during the subsequent electron transfer from the reduced enzyme to a nitroxide spin-label, a one-electron acceptor, an enzyme intermediate has been observed and identified by both optical and EPR spectroscopies as an anionic semiquinone. Results from 1H-NMR spectroscopic studies suggest the possible formation of a substrate carbanion when D-lactate is bound at the active site of D-LDH.

2,6-Dichloroindophenol↗
PubMed1995

Nature and environment of the sulfhydryls of membrane-associated D-lactate dehydrogenase of Escherichia coli.

Ellman's reagent, 5,5'-dithiobis(2-nitrobenzoic acid), has been used to titrate D-lactate dehydrogenase (D-LDH), a respiratory flavoenzyme of Escherichia coli. All six of the possible sulfhydryls titrate in the presence of 2% sodium dodecylsulfate, showing that D-lactate dehydrogenase does not contain any -S-S- bridges. In the native state, only two sulfhydryls are accessible in buffer and only one in the presence of lipid. Single-site mutations of each of the six cysteines of D-lactate dehydrogenase have been prepared. Each of the purified mutant proteins has full activity, demonstrating that an -SH group is not essential to the FAD-driven redox reaction. Ellman's titrations of the mutant proteins have led to the identification of cysteines 65, 146, 156, and 256 in the amino-terminal end as those containing the sulfhydryls that are not accessible in buffer or in buffer plus lipid. The cysteine at 422 is titrated only partially in buffer, while in buffer containing lipid, a necessary factor for full enzymatic activity, its sulfhydryl is inaccessible to the reagent. Cysteine 492 has been identified as containing the sulfhydryl that is accessible to the reagent under both conditions.

Bacterial Outer Membrane Proteins↗
PubMed1994

Structure-activity study of 5-substituted 1-carbobenzoxy-2-iminohydantoins as potential anticonvulsant agents.

On the basis of our previous findings, a series of 5-substituted 2-iminohydantoins has been synthesized and tested for anticonvulsant activity to better understand the SAR of 2-iminohydantoins. Among the compounds tested, (S)-(+)-1-carbobenzoxy-2-iminohydantoin analogs with ethyl (6)-, n-propyl (7a)-, isopropyl (8)-, allyl (9)-, and sec-butyl (11)-substituted groups at the C5 of the iminohydantoin ring provided the best activities against the MES test with ED50 values in the range of 52-74 mg/kg. All of the above compounds except 8 also showed activity against the scMET test with ED50 values in the range of 141-223 mg/kg. All significantly active compounds (1, 6, 7a, 8, 9, and 11) possessed aliphatic hydrocarbon side chains of two- to three-carbon lengths at the C5 position. All of the compounds with no or minimal activity had either shorter or longer side chains. The compounds substituted at the C5 position by aryl groups, arylalkyl groups, or alkyl and arylalkyl groups containing heteroatoms also showed no activity against the MES and scMET tests. The results suggested that the C5 side chain with the correct stereochemistry in 2-iminohydantoins provides optimal anticonvulsant activity when the side chains are aliphatic hydrocarbons with the length, ignoring branching, of two to three carbons.

Animals↗
PubMed1993

A 19F-NMR study of the membrane-binding region of D-lactate dehydrogenase of Escherichia coli.

D-Lactate dehydrogenase (D-LDH) is a membrane-associated respiratory enzyme of Escherichia coli. The protein is composed of 571 amino acid residues with a flavin adenine dinucleotide (FAD) cofactor, has a molecular weight of approximately 65,000, and requires lipids or detergents for full activity. We used NMR spectroscopy to investigate the structure of D-LDH and its interaction with phospholipids. We incorporated 5-fluorotryptophan (5F-Trp) into the native enzyme, which contains five tryptophan residues, and into mutant enzymes, where a sixth tryptophan is substituted into a specific site by oligonucleotide-directed mutagenesis, and studied the 5F-Trp-labeled enzymes using 19F-NMR spectroscopy. In this way, information was obtained about the local environment at each native and substituted tryptophan site. Using a nitroxide spin-labeled fatty acid, which broadens the resonance from any residue within 15 A, we have established that the membrane-binding area of the protein includes the region between Tyr 228 and Phe 369, but is not continuous within this region. This conclusion is strengthened by the results of 19F-NMR spectroscopy of wild-type enzyme labeled with fluorotyrosine or fluorophenylalanine in the presence and absence of a nitroxide spin-labeled fatty acid. These experiments indicate that 9-10 Phe and 3-4 Tyr residues are located near the lipid phase.

DNA Mutational Analysis↗
PubMed1993

[Circumcaval ureter: a review of 5 cases].

From 1985 to 1990, 5 cases of congenital circumcaval ureter were treated. All of the cases were definitely diagnosed by ultrasonography, IVP and retrography. Four of them were confirmed surgically. Ultrasonography was found to be important in the diagnosis of this disease. During the operation, we excised the narrow segment of ureter caused by long term pressing and relocated the ureter behind the inferior vena cava. When rejoining the two ends of ureter, a double "J" stent was put inside the ureter. These procedures are helpful to the healing of incision and could prevent the anastomosis of ureter from restricture.

Adult↗
PubMed1992

[Adrenal medullary phaeochromocytoma and adrenal medullary hyperplasia].

From 1979 to 1989, 8 cases of adrenal medullary phaeochromocytoma (AMP) and 6 cases of adrenal medullary hyperplasia (AMH) were treated surgically. We reviewed the two groups of patients, and the results suggested that though the patients of AMP are similar to those of AMH in clinical symptoms and signs, AMP and AMH are virtually two different diseases of the adrenal medulla. CT and echography are helpful in distinguishing AMP from AMH, but the determination of the two diseases depends on the histological findings. The diagnostic criterion of pathology for AMP and AMH, as well as the treatment of the two diseases are discussed.

Adolescent↗
PubMed1987

[Short-term result of non-Hodgkin's lymphoma treated by the COMP regimen].

From March 1982 to November 1984, 31 patients with non-Hodgkin's lymphoma were treated by COMP regimen. 15 (48%) had stage III and IV lesions. This regimen consisted of cyclophosphamide 600 mg IV weekly, vincristine 2 mg IV weekly, methotrexate 20 mg IM weekly and prednisone 30 mg PO daily for 2-3 weeks. Then, there was an interval of 2 weeks and the same therapy was repeated. 27 patients had more than 3 cycles. Of the 31 patients, 22 gave objective response with an overall response rate of 71%. Among the 22 patients without prior treatment, 10 (45.5%) achieved complete remission (CR) and 8 (36.3%) partial remission (PR)--the overall response rate was 81.8%. 4 (44%) of 9 patients with prior chemotherapy responded to COMP regimen (1 CR and 3 PR). The treatment was well-tolerated. There were only 9 patients with leukocyte count below 4000 and none of them ever below 2000. One patient had a transient elevation of serum glutamic pyruvic transaminase, which dropped to normal very quickly after interruption of the treatment. COMP regimen was as effective as COPP (procarbazine replacing methotrexate) regimen in non-Hodgkin's lymphoma. Hence, it could be considered as a common regimen for advanced non-Hodgkin's lymphoma and used to treat the patients refractory to certain chemotherapeutic agents.

Adolescent↗
PubMedDate not supplied

In vitro effects of epristeride on sperm in rats, dogs and man.

The study was conducted to evaluate in vitro effects of epristeride on sperm in rats, beagle dogs and man. Semen samples were divided into 4 groups and treated with vehicle and epristeride. Motility and motile rate of sperm were videotaped and analyzed with CASA system after 1 h and 2 h incubation periods. Percentage of motile sperm (MOT) of rat sperm decreased after the treatment with epristeride (final concentrations were 0.6, 6 and 60 micromol/L) for 1 h, and MOT of rat sperm treated with middle dose and high dose levels of epristeride also decreased after 2 h, while MOT of dog sperm that treated with three dose levels of epristeride decreased after 2 h. Amplitude of lateral head displacement (ALH) and MOT of human sperm decreased after 2 h with 4.8 micromol/L epristeride treatment. Curvilinear velocity (VCL) and straight-line velocity (VSL) of rat sperm and human sperm changed after 2 h, but there were no significant differences. Therefore, epristeride had a toxic effect on sperm, and the effect varied in different species.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗