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Biomedical subjects

X F Tang

Publications and source records attributed to X F Tang.

At least 19 recordsLinked to original sources
PubMed2001

Anthranilate synthase without an LLES motif from a hyperthermophilic archaeon is inhibited by tryptophan.

Tk-trpE and Tk-trpG, the genes that encode the two subunits of anthranilate synthase from the hyperthermophilic archaeon Thermococcus kodakaraensis KOD1, have been expressed independently in Escherichia coli. The anthranilate synthase complex (Tk-AS complex) was obtained by heat-treatment of the mixture of cell-free extracts containing each recombinant protein, Tk-TrpE (alpha subunit) and Tk-TrpG (beta subunit), at 85 degrees C for 10 min. Further purification of Tk-AS complex was carried out by anion-exchange chromatography followed by gel-filtration. Molecular mass estimations from gel-filtration chromatography indicated that Tk-AS complex was a heterodimer (alphabeta). The complex displayed both ammonia- and glutamine-dependent anthranilate synthase activities, and could not utilize asparagine as an ammonia donor. The optimal pH was pH 10.0 and the optimal temperature was 85 degrees C in both cases. Mg2+ was necessary for the anthranilate synthase activity. At 75 degrees C, the K(m) values of chorismate for ammonia- and glutamine-dependent activities were 13.8 and 3.4 microM, respectively. The K(m) value of Mg2+ was 20.5 microM. The K(m) values of glutamine and NH4Cl were 88 microM and 5.6 mM, respectively. Although Tk-TrpE displayed 47.6% similarity with TrpE of Salmonella typhimurium, conserved amino acid residues proven to be essential for inhibition of enzyme activity by L-tryptophan were not present in Tk-TrpE. Namely, residues corresponding to Glu39, Met293, and Cys465 in the enzyme from S. typhimurium were replaced by Arg28, Thr221, and Ala384 in Tk-TrpE. Nevertheless, significant inhibition by L-tryptophan was observed, with K(i) values of 5.25 and 74 microM for ammonia and glutamine-dependent activities, respectively. The inhibition was competitive with respect to chorismate. The results suggest that the amino acid residues involved in the feedback inhibition by L-tryptophan in the case of Tk-AS complex are distinct from previously reported anthranilate synthases.

Amino Acid Motifs↗
PubMed2001

Interaction of TIP26 from a hyperthermophilic archaeon with TFB/TBP/DNA ternary complex.

Interactions of TBP-interacting protein (TIP26), TBP, and TFB from a hyperthermophilic archaeon Thermococcus kodakaraensis KOD1 with TATA-DNA were examined by electrophoretic mobility shift assay. Tk-TFB formed a ternary complex with Tk-TBP and TATA-DNA. Tk-TIP26 did not inhibit the formation of this ternary complex, but interacted with it to form a TIP26/TFB/TBP/DNA quaternary complex. This interaction is rather weak, and a large excess of Tk-TIP26 over Tk-TBP is required to fully convert the TFB/TBP/DNA ternary complex to the quaternary complex. However, determination of the concentration of Tk-TIP26 and Tk-TBP in KOD1 cells by Western blotting analysis indicated that the concentration of Tk-TIP26 is approximately ten times that of Tk-TBP, suggesting that the quaternary complex might also form in vivo.

Amino Acid Sequence↗
PubMed2000

Biochemical analysis of a thermostable tryptophan synthase from a hyperthermophilic archaeon.

Pyridoxal 5'-phosphate-dependent tryptophan synthase catalyzes the last two reactions of tryptophan biosynthesis, and is comprised of two distinct subunits, alpha and beta. TktrpA and TktrpB, which encode the alpha subunit and beta subunit of tryptophan synthase from a hyperthermophilic archaeon, Thermococcus kodakaraensis KOD1, were independently expressed in Escherichia coli and their protein products were purified. Tryptophan synthase complex (Tk-TS complex), obtained by heat treatment of a mixture of the cell-free extracts containing each subunit, was also purified. Gel-filtration chromatography revealed that Tk-TrpA was a monomer (alpha), Tk-TrpB was a dimer (beta2), and Tk-TS complex was a tetramer (alpha2 beta2). The Tk-TS complex catalyzed the overall alphabeta reaction with a specific activity of 110 micromol Trp per micromol active site per min under its optimal conditions (80 degrees C, pH 8.5). Individual activity of the alpha and beta reactions of the Tk-TS complex were 8.5 micromol indole per micromol active site per min (70 degrees C, pH 7.0) and 119 micromol Trp per micromol active site per min (90 degrees C, pH 7.0), respectively. The low activity of the alpha reaction of the Tk-TS complex indicated that turnover of the beta reaction, namely the consumption of indole, was necessary for efficient progression of the alpha reaction. The alpha and beta reaction activities of independently purified Tk-TrpA and Tk-TrpB were 10-fold lower than the respective activities detected from the Tk-TS complex, indicating that during heat treatment, each subunit was necessary for the other to obtain a proper conformation for high enzyme activity. Tk-TrpA showed only trace activities at all temperatures examined (40-85 degrees C). Tk-TrpB also displayed low levels of activity at temperatures below 70 degrees C. However, Tk-TrpB activity increased at temperatures above 70 degrees C, and eventually at 100 degrees C, reached an equivalent level of activity with the beta reaction activity of Tk-TS complex. Taking into account the results of circular dichroism analyses of the three enzymes, a model is proposed which explains the relationship between structure and activity of the alpha and beta subunits with changes in temperature. This is the first report of an archaeal tryptophan synthase, and the first biochemical analysis of a thermostable tryptophan synthase at high temperature.

Amino Acid Sequence↗
PubMed1996

Guillain-Barré syndrome or "new" Chinese paralytic syndrome in northern China?

A serial study of clinical and magnetic stimulation motor evoked potentials (MEP) was accomplished in 44 patients with the acute flaccid paralytic syndrome which occurred in Northern China in 1991. Control data were provided by 70 healthy subjects from the same area. The cases came from the same area where a so-called new "Chinese paralytic syndrome" had been reported. We found the clinical features of these 44 patients to be similar to those of classical Guillain-Barré. Prolongation of MEP latency at 2 sites or on 2 occasions was found in 36 patients of whom 26 showed obvious clinical and electrophysiological recovery within 4-8 weeks. Three cases showed reduced MEP amplitude with normal latency, but in 2 of them the amplitude recovered in 2-8 weeks. Only 2 cases had no response at all time. We think 41 patients (93.7%) had predominant nerve demyelination. The 3 other patients (6.8%) showed axonal degeneration which is within the range found in previous reports of classical Guillain-Barré. We conclude that the acute paralytic syndrome seen in the summer of 1991 in Northern China represents a classical Guillain-Barré syndrome with demyelination of motor and sensory fibers. There is no reason to consider any special nomenclature such as "Chinese paralytic syndrome" or "acute motor axonal neuropathy."

Adolescent↗
PubMed1991

Magnetic transcranial motor and somatosensory evoked potentials in cervical spondylitic myelopathy.

Fourteen cervical spondylitic myelopathy (CSM) patients were clinically diagnosed and proved by MRI and surgery. The results of 11 patients showed that 8 (72.7%) had motor evoked potential (MEP) abnormality with prolongation of central motor conduction time (CMCT) in 7, and absence of motor action potentials after C7 stimulation in one. Five of the 11 patients showed normal somatosensory evoked potentials (SEPs) along the same arm. The short term (2-4 weeks) follow-up study in 10 patients showed normalization of the prolonged CMCT in one and reappearance of MEPs with C7 stimulation in another. Non-invasive and painless magnetic transcranial stimulation of the motor pathways is useful in the assessment and management of CSM patients, and is better than electrical stimulation.

Adult↗
PubMed1991

[Event-related potential P300 in cerebral infarction].

N1, P2 and P300 potentials were studied in 20 cases of cerebral infarction and 47 healthy controls with standard technique of auditory event-related potentials. Healthy controls of both sexes, different ages, education levels and cognitive capacity did not show apparent differences in the latency of p300 (P greater than 0.05, respectively). The patient group, however, revealed significant (P less than 0.001) prolongation of latency of P300 (mean = 409.6 +/- 50 ms) as compared with 28 well matched healthy subjects (mean = 337.7 +/- 24 ms). Although there was some decline of amplitude of P300 in the patient group, the difference between the control and patient groups was not significant (P greater than 0.05). There was significant difference in the Cognitive Capacity Screening Examination findings between the control and patient groups (P less than 0.01), but it seemed that the evaluation of latency of cognition-related p300 might be more objective and sensitive (P less than 0.001).

Aged↗
PubMed1989

Becker muscular dystrophy.

Five patients from 3 families with Becker muscular dystrophy (BMD) were reported. The main clinical and laboratory findings were in common. Pairs of affected brothers are quite resembled each other. However, there are also some variations among different families. The disease occurred later in the first pair of brothers and was accompanied by macroglossia and red-green color blindness, while the second pair got the disease earlier, which was accompanied by heart impairment. It is interesting that both myogenic and neurogenic changes of EMG can be found in the same patient with BMD in our series.

Adolescent↗
PubMed1989

[Small cell lung cancer with Lambert-Eaton myasthenic syndrome].

Four of 69 cases of small cell lung cancer (SCLC) showed evidence of Lambert-Eaton myasthenic Syndrome (LEMS) were studied neurologically and neurophysiologically in four years. The LEMS appearance were preceded that of SCLC in 3 cases for two years at most. Repeated stimulation of ulnar nerve examination showed diminished amplitude of initial response (0.2-0.9 mv); Amplitude of the response at 3 c/s stimulation for 3 sec was diminished 20-63%. (control 3% decreases-13% increases) but that at 20 c/s stimulation for 10 sec increased 200-800% increases. (control: 20% decreases-56% increases). These findings were important for diagnosis of LEMS. The abnormalities of neurotransmission seems to be due to inadequate release of acetyl choline from nerve terminals at abnormal active zone of Ca++ channels.

Adult↗
PubMed1989

A study of event-related potential P300 in cerebral infarction.

N1, P2 and P300 potentials were studied in 20 cases of cerebral infarction and 47 healthy controls with the standard technique of auditory event-related potentials. Healthy controls of both sexes, different ages, education levels and cognitive capacity did not show apparent differences in the latency of P300 (P greater than 0.05, respectively). The patient group, however, revealed a significant (P less than 0.001) prolongation of latency of P300 (means = 409.6 +/- 50 ms) as compared with 28 well matched healthy subjects (means = 337.7 +/- 24 ms). Although there was a slightly lower amplitude of P300 in the patient group, the difference between control and patient groups was not significant (P greater than 0.05). There was a significant difference in the Cognitive Capacity Screening Examination findings between control and patient groups (P less than 0.01), but it seems that evaluation of the cognition-related latency of P300 may be more objective and sensitive in distinguishing between organic and cognitive distress (P less than 0.001).

Adult↗
PubMed1989

[Clinical and evoked potential studies in 3 cases of "locked-in" syndrome].

Three cases of "Locked in" Syndrome diagnosed by clinical features and CT scan were studied with brainstem auditory and somatosensory evoked potentials. The results were compared with normal values from 22 healthy subjects. The results suggested that these two evoked potentials may be useful for the localization of "Locked-in" syndrome.

Adult↗
PubMed1989

[Relation of optic myelitis (OM) and multiple sclerosis (MS)].

Brainstem auditory evoked potentials (BAEP) were studied on 38 optic myelitis (OM) and 16 of myelopathy with definite abnormal VEP. Forty-two normal subjects were studied for comparison. The results showed that BAEP were abnormal in 42% of the OM and 38% of the latter myelopathy groups. Among the abnormal BAEP 82% showed V wave abnormality, 32% prolongation in I-III or III-V interpeak latency or absence of III wave, and 59% with unilateral lesions. These findings would imply that the lesions were mostly on the white matter and small and localized in character which was compatible with the pathology of MS. 41% of BAEP abnormality in these two groups showed a lesion would be in the brainstem in almost half of these two types of disorders. OM would be most likely a clinical variant type of MS and not a unique disease.

Adolescent↗