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Biomedical subjects

P Cheung

Publications and source records attributed to P Cheung.

18 recordsLinked to original sources
PubMed1992

Synthetic peptide of the sequence 632-642 on myosin subfragment 1 inhibits actomyosin ATPase activity.

A synthetic peptide corresponding to a sequence 632-642 (S632-642) on the myosin subfragment 1 (S-1) heavy chain and spanning the 50/20 kDa junction of S-1 binds to actin in the presence and absence of S-1. The binding of 1.0 mole of peptide per actin causes almost complete inhibition of actomyosin ATPase activity and only partial inhibition of S-1 binding to actin. The binding of S632-642 to the N-terminal segment of actin is supported by competitive carbodiimide cross-linking of S-1 and S632-642 to actin and the catalytic properties of cross-linked acto-S-1 and actin-peptide complexes. These results show that the sequence 632-642 on S-1 is an autonomous binding site for actin and confirm the catalytic importance of its interactions with the N-terminal segment of actin.

Actins↗
PubMed1992

Mouse cortical collecting duct cells show nonselective cation channel activity and express a gene related to the cGMP-gated rod photoreceptor channel.

Apical nonselective cation channels with an average single-channel conductance of 34 +/- 2.3 pS were found in M-1 mouse cortical collecting duct cells. Channel activity is increased by depolarization and abolished by cytoplasmic calcium removal. Cytoplasmic application of 0.1 mM cGMP decreases channel open probability by 27%. cDNAs corresponding to approximately 40% of the coding region of the photoreceptor channel were isolated by the polymerase chain reaction from M-1 cells and a rat kidney cDNA library. The rat kidney-derived sequence differs by a single base, and the M-1-cell-derived sequence differs by only two bases, from the photoreceptor sequence. A second clone from M-1 cells differs by 20 out of 426 bases from the photoreceptor sequence. In all three clones, the deduced amino acid sequence is identical to that of the rat photoreceptor channel. Northern blot analysis of poly(A)+ RNA from M-1 cells reveals the presence of a 3.2-kilobase band hybridizing with a retinal cGMP-gated cation channel probe. The results suggest the expression in M-1 cells of more than one gene coding for nonselective cation channels or channel subunits, one of which is identical to the cGMP-gated cation channel gene of rod photoreceptors.

Animals↗
PubMed1992

Identification of G-proteins in rat parotid gland plasma membranes and granule membranes: presence of distinct components in granule membranes.

We have identified by immunoblotting and ADP-ribosylation by cholera toxin and pertussis toxin the presence of Mr 43 and 46 KDa Gs alpha, and 39 and 41 KDa Gi alpha subunits in rat parotid gland plasma membranes but not in granule membranes. A Mr 28 KDa polypeptide that served as substrate for ADP-ribosylation by both cholera toxin and pertussis toxin was present exclusively in granule membranes. Photoaffinity crosslinking of [alpha-32P]GTP showed the presence of high molecular weight GTP-binding proteins (Mr 160, 100 KDa) in granule membranes. Six low molecular weight GTP-binding proteins (Mr 21-28 KDa) were differentially distributed in both plasma membranes and granule membranes. The present study identifies various GTP-binding proteins in rat parotid gland plasma membranes and granule membranes, and demonstrates the presence of distinct molecular weight GTP-binding proteins in granule membranes. These granule-associated GTP-binding proteins may be involved in secretory processes.

Amylases↗
PubMed1992

Suicide precautions for psychiatric inpatients: a review.

This paper reviews the literature on the assessment and management of suicide risk of psychiatric inpatients. Even though a large number of scales have been developed to assist the prediction of suicide for patients admitted for suicide ideas and attempts, none of them were designed to predict suicide in the short term. However the Modified Suicide Intent Scale and the Hopelessness Scale appear to have the potential to predict immediate suicide risk. Risk factors associated with specific psychiatric conditions were all derived retrospectively and their predictive validities have not been established by prospective studies. Important issues relating to the management of suicidal inpatients, such as staff-patient relationships, use of constant observation and medical-legal aspects are reviewed.

Hospitalization↗
PubMed1992

Psychiatric morbidity among Dunedin Chinese women.

A community postal survey of minor psychiatric morbidity among Chinese women living in Dunedin was conducted. The 28-item version of the General Health Questionnaire (GHQ-28) was used as the case identification instrument. The overall rate of psychiatric morbidity of Dunedin Chinese women did not differ from their European counterparts. The sociodemographic factors found to be associated with minor psychiatric morbidity included having no children, and being either very well or very poorly educated. Among (foreign born) migrants, those who were born in China, whose reason for migration was "follow the lead of their family" or "family reunion", had resided in New Zealand for ten years or more and spoke English infrequently tended to have higher psychiatric morbidity.

Adolescent↗
PubMed1991

Isolation and characterization of a full-length cDNA encoding the 55-kDa rabbit zona pellucida protein.

A full-length cDNA (rc55) encoding the major rabbit zona pellucida (ZP) glycoprotein (55 kDa) has been cloned and sequenced. A lambda gt11 expression library was constructed using poly(A)+ mRNA isolated from sexually immature rabbit ovaries which contain large numbers of developing follicles. The rc55 cDNA was identified using affinity purified polyclonal antibodies specific to ZP antigens which are shared among mammalian species. The deduced amino acid sequence of the full-length rc55 clone was matched to the NH2-terminal 25-amino acid sequence obtained for this protein. The predicted amino acid sequence consists of 540 amino acids including a putative signal peptide of 18-24 residues and six potential N-glycosylation sites. The cDNA hybridizes to a 2000-base species of mRNA from rabbit ovary which is not detected in other rabbit tissues. The message is present early in ovarian follicular development and is approximately 600-fold greater in sexually immature as compared with sexually mature rabbit ovaries. This cDNA was expressed as a cro-beta-galactosidase fusion protein using the pEX expression vector. Antibodies against native rabbit ZP, affinity-purified on the recombinant 55-kDa ZP protein, were found to recognize the native rabbit ZP glycoprotein, indicating partial conservation of native epitopes in the expressed recombinant protein.

Amino Acid Sequence↗
PubMed1991

Catalytic cooperativity induced by SH1 labeling of myosin filaments.

Modifications of SH1 groups on isolated myosin subfragment 1 (S-1) and myosin in muscle fibers affect differently the acto-S-1 ATPase and the fiber properties. Consistent with the findings of earlier work on fibers, the modification of SH1 groups in relaxed myofibrils with phenylmaleimide caused a loss of their shortening. This loss paralleled the decrease in the Vmax of extracted myosin but was not linear with the extent of SH1 labeling. Strikingly, the decrease in Vmax of S-1 prepared from the modified myofibrils was directly proportional to the extent of SH1 labeling. The specificity of SH1 labeling in myofibrils was verified by ATPase activities, thiol titrations, radiolabeling experiments, and comparisons to myosin labeled on SH1 in solution. To test for intermolecular interactions in the myosin filaments and their contribution to the differences between S-1 and myosin, the catalytic properties of copolymers of myosin were examined. Copolymers of myosin and rod minifilaments were formed in 5 mM citrate-Tris (pH 8.0) buffer, and their homogeneity was verified by sedimentation velocity analysis. The inhibition of actomyosin ATPase by rod particles was related to the decrease in the Km value. When rod particles were replaced in these minifilaments by SH1-modified myosin, the ATPase of the copolymers was increased over that of the combined ATPases of the individual filaments. The actomyosin ATP turnover rates on the unmodified heads were increased severalfold by the modified heads.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1991

Adult psychiatric epidemiology in China in the 80s.

This paper presents the prevalence rates of the main adult psychiatric disorders as determined by seven community surveys conducted in China in the 1980s. The prevalence rates are compared with previous findings in China and those from Taiwan and the West.

Adult↗
PubMed1991

Creatine kinase isoenzyme band mimicking CK MB on agarose gel electrophoresis.

The authors report the case of an 80-year-old man with prostatic disease whose serum contained an aberrant band in the MB position on agarose gel electrophoresis of creatine kinase (CK) isoenzymes. The authors demonstrated that the band probably was CK BB; the patient had no evidence of myocardial infarction. Contrary to most previous reports of such cases, the aberrant enzyme did not appear to be linked with IgG, IgA, or IgM; it also did not behave as if attached to a chelatable cation. Care must be taken to avoid mistaking such bands for CK MB.

Aged↗
PubMed1991

Brefeldin A arrests the maturation and egress of herpes simplex virus particles during infection.

Herpes simplex virus (HSV) requires the host cell secretory apparatus for transport and processing of membrane glycoproteins during the course of virus assembly. Brefeldin A (BFA) has been reported to induce retrograde movement of molecules from the Golgi to the endoplasmic reticulum and to cause disassembly of the Golgi complex. We examined the effects of BFA on propagation of HSV type 1. Release of virions into the extracellular medium was blocked by as little as 0.3 microgram of BFA per ml when present from 2 h postinfection. Characterization of infected cells revealed that BFA inhibited infectious viral particle formation without affecting nucleocapsid formation. Electron microscopic analyses of BFA-treated and untreated cells (as in control cells) demonstrated that viral particles were enveloped at the inner nuclear membrane in BFA-treated cells and accumulated aberrantly in this region. Most of the progeny virus particles observed in the cytoplasm of control cells, but not that of BFA-treated cells, were enveloped and contained within membrane vesicles, whereas many unenveloped nucleocapsids were detected in the cytoplasm of BFA-treated cells. This suggests that BFA prevents the transport of enveloped particles from the perinuclear space to the cytoplasmic vesicles. These findings indicate that BFA-induced retrograde movement of molecules from the Golgi complex to the endoplasmic reticulum early in infection arrests the ability of host cells to support maturation and egress of enveloped viral particles. Furthermore, we demonstrate that the effects of BFA on HSV propagation are not fully reversible, indicating that maturation and egress of HSV type 1 particles relies on a series of events which cannot be easily reconstituted after the block to secretion is relieved.

Animals↗
PubMed1991

Calcium uptake in rat parotid gland secretory granules.

45Ca2+ uptake in isolated rat parotid secretory granules was examined in the presence of oxalate. Uptake of calcium was dependent on time, with the maximum occurring at 15 min. The uptake of calcium was dependent on adenosine-5'-triphosphate (ATP), and substitution of ATP with beta, gamma-methylene-ATP did not stimulate calcium uptake. Enzyme marker analysis indicated that mitochondria accounted for no greater than 3.0 +/- 0.2% of the observed ATP-dependent calcium uptake. Calcium uptake was blocked by the ATPase inhibitors tributyltin, IC50 = 12.2 +/- 0.6 nmol/L and 4-acetamido-4'-isothiocyano-2,2'-stilbene disulphonic acid (SITS), IC50 = 3.0 +/- 0.3 mumol/L. These results indicate that in the parotid secretory granule there is a calcium uptake mechanism that is dependent on the hydrolysis of ATP and is suppressed by two inhibitors of granule ATPase.

Adenosine Triphosphate↗
PubMed1976

A simple method for "reference range" estimation from routine laboratory data.

A simplified method is presented to estimate reference ranges from hospital laboratory data. It is based on a combination of graphical estimation of relative sizes of normal and abnormal populations and the "mode-center" concept in which the mode of the total population centers on the 50% cumulative frequency of the normal population. This method can be applied to determine reference ranges even though the data source contains abnormally high and/or low values. The reference ranges obtained for BUN and calcium from in-patient and out-patient sources by this method were found to be similar to those reported for "healthy" subjects.

Blood Urea Nitrogen↗