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Biomedical subjects

X Q Liu

Publications and source records attributed to X Q Liu.

At least 73 records · Page 4Linked to original sources
PubMed1994

The Chlamydomonas chloroplast clpP gene contains translated large insertion sequences and is essential for cell growth.

Sequence determination of the chloroplast clpP gene from two distantly related Chlamydomonas species (C. reinhardtii and C. eugametos) revealed the presence of translated large insertion sequences (IS1 and IS2) that divide the clpP gene into two or three sequence domains (SDs) and are not found in homologous genes in other organisms. These insertion sequences do not resemble RNA introns, and are not spliced out at the mRNA level. Instead, each insertion sequence forms a continuous open reading frame with its upstream and downstream sequence domains. IS1 specifies a potential polypeptide sequence of 286 and 318 amino acid residues in C. reinhardtii and C. eugametos, respectively. IS2 encodes a 456 amino acid polypeptide and is present only in C. eugametos. The two Chlamydomonas IS1 sequences show substantial similarity; however, there is no significant sequence similarity either between IS1 and IS2 or between these insertion sequences and any other known protein coding sequences. The C. reinhardtii clpP gene was further shown to be essential for cell growth, as demonstrated through targeted gene disruption by particle gun-mediated chloroplast transformation. Only heteroplasmic transformants could be obtained, even under mixotrophic growth conditions. The heteroplasmic transformants were stable only under selection pressure for the disrupted clpP, rapidly segregated into wild-type cells when the selection pressure was removed, and grew significantly more slowly than wild-type cells under phototrophic conditions.

ATP-Dependent Proteases↗
PubMed1994

Serum micronutrients in relation to pre-cancerous gastric lesions.

Serum levels of retinol, beta-carotene, ascorbic acid, alpha-tocopherol, selenium, ferritin, copper, and zinc were assayed for approximately 600 adults aged 35 to 64 with pre-cancerous gastric lesions in an area of China with one of the world's highest rates of stomach cancer. Previous studies have shown that the cancers generally are preceded by chronic atropic gastritis (CAG), intestinal metaplasia (IM) and dysplasia. Concentrations of beta-carotene and ascorbic acid were significantly lower among individuals with IM than among those whose most severe lesion was superficial gastritis or CAG. The associations with IM for these nutrients were strong and independent. In combination, the odds of CAG progressing to IM were only 1/6 as high among those with upper tertile levels of beta-carotene and ascorbic acid as among those with lower tertile levels of both nutrients. The serum levels of beta-carotene and ascorbic acid were similar for individuals having IM with or without accompanying dysplasia. Risk of IM was also somewhat increased among those with low serum ferritin, but no significant effects were observed in multivariate analyses for the other nutrients assayed. The findings point to a major influence of specific nutrient deficits in the mechanisms of gastric carcinogenesis in this high-risk area.

Adult↗
PubMed1993

The unusual rps3-like orf712 is functionally essential and structurally conserved in Chlamydomonas.

The Chlamydomonas reinhardtii chloroplast orf712 is a previously described open reading frame that lacks a detectable transcript but potentially encodes a polypeptide with sequence similarities to ribosomal protein Rps3 only at its N- and C-termini. Here we report that orf712 is an essential gene, as demonstrated through gene disruption by particle gun-mediated chloroplast transformation. We also show that an orf712 is present and structurally conserved in all of the two or three major Chlamydomonas lineages. Our results suggest that orf712 is an unusual rps3 gene that contains a large translated intervening sequence.

Amino Acid Sequence↗
PubMed1993

Chloroplast chlB gene is required for light-independent chlorophyll accumulation in Chlamydomonas reinhardtii.

Light-independent chlorophyll synthesis occurs in some algae, lower plants, and gymnosperms, but not in angiosperms. We have identified a new chloroplast gene, chlB, that is required for the light-independent accumulation of chlorophyll in the green alga Chlamydomonas reinhardtii. The chlB gene was cloned, sequenced, and then disrupted by performing particle gun-mediated chloroplast transformation. The resulting homoplasmic mutant was unable to accumulate chlorophyll in the dark and thus exhibited a 'yellow-in-the-dark' phenotype. The chlB gene encodes a polypeptide of 688 amino acid residues, and is distinct from two previously characterized chloroplast genes (chlN and chlL) also required for light-independent chlorophyll accumulation in C. reinhardtii. Three unidentified open reading frames in chloroplast genomes of liverwort, black pine, and Chlamydomonas moewusii were also identified as chlB genes, based on their striking sequence similarities to the C. reinhardtii chlB gene. A chlB-like gene is absent in chloroplast genomes of tobacco and rice, consistent with the lack of light-independent chlorophyll synthesis in these plants. Polypeptides encoded by the chloroplast chlB genes also show significant sequence similarities with the bchB gene product of Rhodobacter capsulatus. Comparisons among the chloroplast chlB and the bacterial bchB gene products revealed five highly conserved sequence areas that are interspersed by four stretches of highly variable and probably insertional sequences.

Algal Proteins↗
PubMed1993

Plasma bevantolol concentration and heart rate in rabbits.

Bevantolol (Bev, 5, 10 mg.kg-1) was injected i.v. to rabbits. A measure the lag time of heart rate (HR) response behind the changes in plasma Bev concentration (K(eo)), and the sensitivity of the site of action of Bev (EC50) were determined. The K(eo) were 0.03 +/- 0.02 and 0.029 +/- 0.009 min-1 and the EC50 were 0.2 +/- 0.1 and 0.27 +/- 0.14 microgram.ml-1 respectively for the 2 dosages. The peak changes in HR lagged behind the changes in plasma Bev concentration. There were no significant changes in both pharmacokinetic and pharmacodynamic parameters between the dosages.

Adrenergic beta-Antagonists↗
PubMed1993

[131I-ortho-iodohippurate renography in the staging of malignant lymphoma].

Malignant lymphoma is a systemic disease with many organs involved. According to autopsy reports, the frequency of kidney involvement was 60% and with no symptoms, signs and serum biochemical abnormalities in most of the patients. 131I-sodium orthoiodohippurate (131I-OIH) renography examination was performed in 33 malignant lymphoma cases. It was abnormal in 20 cases (60.6%). Major abnormalities were tb, C1/2 extension and decrease in RI. "Obstructive type" renography could be found in a number of the patients. An obstructive type renography seen in one patient showed improvement after chemotherapy, but autopsy revealed that both kidneys were involved. It suggested that the renography abnormality was related to tumor infiltration. Among the 33 cases, there were 13 abnormal renographies in I-III stage patients. Examination was performed in 8 cases both before and after chemotherapy, and their renographies were improved after chemotherapy (remission rate 100%). Therefore, we believe that renography examination is advantageous to make accurate staging of malignant lymphoma.

Humans↗
PubMed1992

Cytogenetic studies of eight primary gastric cancers.

Cytogenetic analysis was performed on eight primary gastric cancers. Three of them had simple chromosome changes: 47,XX,+X/48,XX,+X,+X; 48,XX,+8,+19,t(3;5) (q21;q31) and 47,XY,+del(7)(q22). The five others had complicated chromosome changes; both 3p- and 7q- were noted in four cases and i(5p) was noted in two cases.

Adenocarcinoma↗
PubMed1992

Multiple SH2-mediated interactions in v-src-transformed cells.

The Src homology 2 (SH2) domain is a noncatalytic region which is conserved among a number of signaling and transforming proteins, including cytoplasmic protein-tyrosine kinases and Ras GTPase-activating protein (GAP). Genetic and biochemical data indicate that the SH2 domain of the p60v-src (v-Src) protein-tyrosine kinase is required for full v-src transforming activity and may direct the association of v-Src with specific tyrosine-phosphorylated proteins. To test the ability of the v-Src SH2 domain to mediate protein-protein interactions, v-Src polypeptides were expressed as fusion proteins in Escherichia coli. The bacterial v-Src SH2 domain bound a series of tyrosine-phosphorylated proteins in a lysate of v-src-transformed Rat-2 cells, including prominent species of 130 and 62 kDa (p130 and p62). The p130 and p62 tyrosine-phosphorylated proteins that complexed v-Src SH2 in vitro also associated with v-Src in v-src-transformed Rat-2 cells; this in vivo binding was dependent on the v-Src SH2 domain. In addition to binding soluble p62 and p130, the SH2 domains of v-Src, GAP, and v-Crk directly recognized these phosphotyrosine-containing proteins which had been previously denatured and immobilized on a filter. In addition, the SH2 domains of GAP and v-Crk bound to the GAP-associated protein p190 immobilized on a nitrocellulose membrane. These results show that SH2 domains bind directly to tyrosine-phosphorylated proteins and that the Src SH2 domain can bind phosphorylated targets of the v-Src kinase domain.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

[Effects of amiodarone on kinetics of procainamide and its major metabolite disposition in rabbit].

The effects of steady state amiodarone on the kinetics of procainamide (PA) and its major metabolite, acetylprocainamide (NAPA), disposition in rabbits were examined. When PA was given alone, the pharmacokinetic parameters alpha, beta, Kmo, K1m.V1.V-1m, were 0.20 +/- 0.04, 0.016 +/- 0.003, 0.027 +/- 0.01, and 0.043 +/- 0.02 min-1, respectively. When PA was given in combination with amiodarone, the corresponding values were 0.37 +/- 0.08, 0.0059 +/- 0.002, 0.0096 +/- 0.004, and 0.016 +/- 0.003 min-1, respectively. The results indicated that the disposition kinetics of both PA and NAPA were significantly changed by steady state amiodarone.

Acecainide↗
PubMed1991

The plastid genome of Cryptomonas phi encodes an hsp70-like protein, a histone-like protein, and an acyl carrier protein.

The plastid genome of Cryptomonas phi, a cryptomonad alga, contains three genes that have not previously been found in any organellar genome. Each of these genes encodes a functional class of organellar gene product not previously reported. The first gene, dnaK, encodes a polypeptide of the hsp70 heat shock protein family. The predicted amino acid sequence of the DnaK protein is 54% identical to that of the Escherichia coli hsp70 protein (DnaK), 50-53% identical to that of two nucleus-encoded mitochondrial hsp70 proteins, and 43-46% identical to that of several eukaryotic cytoplasmic members of the hsp70 protein family. The second gene, hlpA, encodes a polypeptide resembling bacterial histone-like proteins. The predicted amino acid sequence of the HlpA protein is 25-53% identical to that of several bacterial histone-like proteins, and the identity increases to 39-76% over a conserved region corresponding to the long arm that binds DNA. The third gene, acpA, encodes an acyl carrier protein, which is a key cofactor in the synthesis and metabolism of fatty acids. Its predicted amino acid sequence is 36-59% identical to that of eubacterial and plant chloroplast (nucleus-encoded) acyl carrier proteins.

Acyl Carrier Protein↗
PubMed1991

High-performance liquid chromatographic assay for amiloride in plasma and urine.

A sensitive and simplified high-performance liquid chromatographic procedure has been developed for quantification of amiloride in rabbit plasma, as well as human plasma and urine. Following protein precipitation with perchloric acid, the supernatant was directly injected into a C18 Nucleosil column. The mobile phase consisted of methanol-water (45:55) containing 0.1 M perchloric acid, and the compound was quantitated using a fluorescence detector at excitation and emission wavelengths of 286 and 418 nm, respectively. The average recovery was 97.6%. The calibration curve was linear over the range 2.0-20.0 ng/ml. The limit of detection was 0.5 ng/ml.

Administration, Oral↗
PubMed1991

The epidermal growth factor receptor phosphorylates GTPase-activating protein (GAP) at Tyr-460, adjacent to the GAP SH2 domains.

GTPase-activating protein (GAP) stimulates the ability of p21ras to hydrolyze GTP to GDP. Since GAP is phosphorylated by a variety of activated or oncogenic protein-tyrosine kinases, it may couple tyrosine kinases to the Ras signaling pathway. The epidermal growth factor (EGF) receptor cytoplasmic domain phosphorylated human GAP in vitro within a single tryptic phosphopeptide. The same GAP peptide was also apparently phosphorylated on tyrosine in EGF-stimulated rat fibroblasts. Circumstantial evidence suggested that residue 460 might be the site of GAP tyrosine phosphorylation. This possibility was confirmed by phosphorylation of a synthetic peptide corresponding to the predicted tryptic peptide containing Tyr-460. Alteration of Tyr-460 to phenylalanine by site-directed mutagenesis diminished the in vitro phosphorylation of a bacterial GAP polypeptide by the EGF receptor. We conclude that Tyr-460 is a site of GAP tyrosine phosphorylation by the EGF receptor in vitro and likely in vivo. GAP Tyr-460 is located immediately C terminal to the second GAP SH2 domain, suggesting that its phosphorylation might have a role in regulating protein-protein interactions.

Amino Acid Sequence↗
PubMed1991

Infantile spasms. A retrospective study of 105 cases.

This paper is a summary of our observations on 105 cases of infantile spasms. The age of onset was around six months after birth, but the patients came for treatment mainly about one year after onset. Fever of unknown cause, asphyxia, birth injury, infection of the central nervous system, tuberous sclerosis, phenylketonuria and recent immunization etc. were complained. Clinically, it is characterized by head nodding, mental retardation, myoclonic jerks and various neurologic deficits. EEG findings showed classical or modified arrythmia or other epileptiform patterns. About one third of 22 cases examined had abnormal brain stem auditory evoked potentials. Among 42 patients who underwent CT scanning before ACTH treatment, 18 were normal and 7 abnormal; during ACTH treatment 3 normal and 4 abnormal; after completion of treatment, 4 normal and 6 abnormal, suggesting no further atrophy of the brain. Examination of trace elements of the hair by particle-induced X-ray emission (PIXE) method in 23 patients revealed a significant difference in lead, calcium and zinc contents between patients and 101 controls, but no statistical difference in iron and copper contents between the two groups. Sodium valproate, prednisone and ACTH appear to be effective in the treatment of infantile spasms. Eight patients fully recovered, and they can go to school without difficulty. Many patients derived various degrees of improvement to the satisfaction of their parents. Two patients were still amented and often attacked by myoclonus. The effects, side effects of these drugs, and the possible pathogenesis were discussed.

Adrenocorticotropic Hormone↗
PubMed1991

[Combined pharmacokinetic and pharmacodynamic model analysis for procainamide and its metabolite].

The pharmacokinetic and pharmacodynamic profiles of procainamide (PA) and its major metabolite, acetylprocainamide (NAPA), were analyzed by extended combined pharmacokinetic and pharmacodynamic model in rabbits. The pharmacodynamic parameters Keo, S, Ce(50), Emax for PA were 0.023 +/- 0.005 min-1, 3.9 +/- 1.1, 3.6 +/- 0.9 micrograms.ml-1, 37 +/- 10 ms respectively and for NAPA were 0.061 +/- 0.017 min-1, 2.2 +/- 0.4, 6.2 +/- 1.7 micrograms.ml-1, 53.6 +/- 2.5 ms. Following PA iv to rabbit both PA and NAPA were involved in the QTc prolongation of the initial period, but the later action was mainly associated with NAPA. Differences of pharmacokinetic and pharmacodynamic parameters between PA and NAPA were found.

Acecainide↗
PubMed1991

Tyrosine phosphorylation of GAP and GAP-associated proteins in lymphoid and fibroblast cells expressing lck.

The Ras GTPase activating protein (GAP) is a strong candidate for the protein that links protein-tyrosine kinases to the Ras mitogenic pathway. GAP and two associated proteins, p62 and p190, were shown to be phosphorylated on tyrosine in the LSTRA thymoma cell line, in which the p56lck tyrosine kinase is overexpressed as a result of retroviral promoter insertion. In NIH3T3 fibroblasts expressing specific oncogenic and transformation-defective variants of p56lck, we found that the tyrosine phosphorylation of GAP complexes required both enzymatic activation and myristylation of p56lck, and correlated with lck transforming activity. The interaction between p62 and p190 from lck-transformed fibroblasts and GAP could be reconstituted in vitro using bacterial TrpE fusion proteins containing GAP Src homology 2 (SH2) domains. In vitro complex formation was insensitive to the prior denaturation of SH2 ligands, suggesting that SH2-binding sites are formed by linear peptide sequences. These results suggest that the tyrosine phosphorylation of GAP, and its interactions with SH2-binding proteins, may be involved in fibroblast transformation by activated lck, and may participate in signal transduction and cellular transformation in lymphoid cells.

Animals↗
PubMed1990

An amino-terminal signal sequence abrogates the intrinsic membrane-targeting information of mitochondrial uncoupling protein.

Mitochondrial uncoupling protein, a polytopic integral protein of the inner membrane, is initially made in the cytoplasm as a soluble polypeptide (307 amino acids) lacking a cleavable targeting (signal) peptide. Earlier studies (Liu, X., Bell, A. W., Freeman, K. B., and Shore, G. C. (1988) J. Cell Biol. 107, 503-509) identified internal regions of the molecule that are critical for targeting and membrane insertion. Here, we demonstrate that the ability of uncoupling protein to insert into the inner membrane is abrogated when the molecule is fused behind the matrix-targeting signal of preornithine carbamyltransferase; the hybrid protein was imported across the inner membrane and deposited in the matrix where it was processed. In this context, however, the processed product remained in the matrix and was incapable of inserting into the inner membrane.

Animals↗