Search PubMed⌕ Search

Biomedical subjects

M Y Cheng

Publications and source records attributed to M Y Cheng.

13 recordsLinked to original sources
PubMed1990

The mitochondrial chaperonin hsp60 is required for its own assembly.

Heatshock protein 60 (hsp60) in the matrix of mitochondria is essential for the folding and assembly of newly imported proteins. Hsp60 belongs to a class of structurally related chaperonins found in organelles of endosymbiotic origin and in the bacterial cytosol. Hsp60 monomers form a complex arranged as two stacked 7-mer rings. This 14-mer complex binds unfolded proteins at its surface, then seems to catalyse their folding in an ATP-dependent process. The question arises as to how such an assembly machinery is itself folded and assembled. Hsp60 subunits are encoded by a nuclear gene and translated in the cytosol as precursors which are translocated into mitochondria and proteolytically processed. In both intact cells and isolated mitochondria of the hsp60-defective yeast mutant mif4, self-assembly of newly imported wild-type subunits is not observed. Functional pre-existing hsp60 complex is required in order to form new, assembled, 14-mer. Subunits imported in vitro are assembled with a surprisingly fast half-time of 5-10 min, indicative of a catalysed reaction. These findings are further evidence that self-assembly may not be the principal mechanism by which proteins attain their functional conformation in the intact cell.

Biological Transport↗
PubMed1990

Anaemia and thalassaemia in healthy adolescents from southern Chinese families.

A study was conducted on 447 healthy high school students of southern Chinese descent to determine the prevalence of anaemia and thalassaemia. Haematological data and serum ferritin levels were determined on all venous blood samples. Haemoglobin (Hb) electrophoretic study was conducted on 43 students who had anaemia (Hb less than 12 g/dL), and/or mean corpuscular volume (MCV) less than 80 fL. They were re-assessed after 1 month of oral iron therapy. Three girls had definite iron deficient anaemia (less than 1%). Thirty-nine students had either alpha, or beta-thalassaemia, only seven of whom showed anaemia. Since the overwhelming majority of both the thalassaemic students (38 of 39) and the participants (429 of 447) were of Cantonese extraction (native of Guangdong province), the overall incidence of 8.8% (alpha-thalassaemia 5.4%, beta-thalassaemia 3.4%) reflected the high frequency of the thalassaemia gene among this group of southern Chinese. MCV measurement, rather than Hb, was more useful in its detection.

Adolescent↗
PubMed1988

The processing peptidase of yeast mitochondria: the two co-operating components MPP and PEP are structurally related.

Two proteins co-operate in the proteolytic cleavage of mitochondrial precursor proteins: the mitochondrial processing peptidase (MPP) and the processing enhancing protein (PEP). In order to understand the structure and function of this novel peptidase, we have isolated mutants of Saccharomyces cerevisiae which were temperature sensitive in the processing of mitochondrial precursor proteins. Here we report on the mif2 mutation which is deficient in MPP. Mitochondria from the mif2 mutant were able to import precursor proteins, but not to cleave the presequences. The MPP gene was isolated. MPP is a hydrophilic protein consisting of 482 amino acids. Notably, MPP exhibits remarkable sequence similarity to PEP. We speculate that PEP and MPP have a common origin and have evolved into two components with different but mutually complementing functions in processing of precursor proteins.

Amino Acid Sequence↗
PubMed1988

Anticoagulation with sodium warfarin in children: effect of a loading regimen.

To assess dose requirements of warfarin in children, we analyzed retrospectively the treatment of 26 patients with the drug. Subsequently we treated 15 children, prospectively, with a regimen derived from our retrospective analysis (0.2 mg/kg/day for 2 days). In the retrospective analysis we found the prothrombin time (PT) at day 2 to correlate significantly with the dose given on day 0 (p less than 0.001) and with the cumulative dose on days 0 and 1 (p less than 0.001), but the standardized loading regimen resulted in a wide range of PTs independent of age, weight, or body surface area. The warfarin dose contributes only 40% of the variability in PT; an individual child's response to warfarin cannot be predicted accurately on the basis of the usual morphometric measurements.

Child↗
PubMed1987

Congenital mesoblastic nephroma: a clinicoradiologic study of 17 cases representing the pathologic spectrum of the disease.

Congenital mesoblastic nephroma (CMN) is a rare infantile renal tumor with a generally excellent prognosis. We describe 17 tumors that fit into the pathologic spectrum of CMN proposed by Beckwith, which ranges from benign renal tumors, through atypical "gray zone" lesions of more aggressive potential, to "crossover" tumors akin to clear cell sarcoma of kidney. Nine patients with histologically typical CMN were significantly younger and had smaller tumors than did eight patients with atypical CMN. Clinical features did not differ in the two groups of patients. A distinctive "ring sign" on renal sonography was commonly seen in patients with typical intrarenal CMN. All 17 patients were alive with no evidence of disease at a mean follow-up of 10 years. Nephrectomy was adequate therapy for younger infants and for those with typical CMN. Nephrectomy was probably also adequate therapy for infants 3 months of age or younger with atypical CMN, even if the tumor extended to the surgical resection margins and into the perinephric connective tissues. Adjuvant chemotherapy or radiation or both should be reserved for patients older than 3 months who have grossly unresected tumors and for those patients whose tumors have an unequivocally malignant histologic appearance or evidence of aggressive biologic behavior.

Age Factors↗
PubMed1987

Import and processing of human ornithine transcarbamoylase precursor by mitochondria from Saccharomyces cerevisiae.

Expression of the subunit precursor of the human mitochondrial matrix enzyme ornithine transcarbamoylase (OTCase; EC 2.1.3.3) was programmed in Saccharomyces cerevisiae from a 2-micron plasmid by using an inducible galactose operon promoter. In the presence of the inducing sugar (galactose), two polypeptides were specifically precipitable with anti-OTCase antiserum: the human OTCase precursor (40 kDa); and the mature OTCase subunit (36 kDa). When yeast cells containing these species were lysed and fractionated, the OTCase precursor was found to be associated with mitochondrial membranes, while the mature subunit was found partly with mitochondrial membranes and partly in the soluble mitochondrial matrix-containing fraction. When OTCase enzymatic activity was assayed in fractions similarly derived from an S. cerevisiae strain devoid of yeast OTCase activity (an arg3 mutant) but expressing human OTCase, activity was detected specifically in the mitochondrial matrix fraction. A mutant human OTCase precursor containing an artificial mutation in the NH2-terminal leader peptide (arginine-23 to glycine) was similarly examined. As was previously observed with mammalian mitochondria, this precursor failed both to reach the matrix compartment and to be proteolytically processed; it also failed to exhibit OTCase enzymatic activity. Presence of OTCase enzymatic activity in an arg3 strain expressing wild-type precursor was utilized to obtain selective growth in a medium devoid of arginine but supplemented with the OTCase substrate ornithine. We conclude that, during evolution, the pathway of mitochondrial import utilized by the human OTCase precursor is conserved between yeast and humans, and that, by using selective growth conditions, it may be possible to examine genetically this pathway in S. cerevisiae.

Enzyme Precursors↗
PubMed1986

Chromosome analysis on a cell line (CE48T/VGH) derived from a human esophageal carcinoma.

The cell line CE48T/VGH was established from an epidermoid carcinoma of the middle third of the esophagus of a 58-year-old male patient. Cytogenetic analysis at passages 90-99 showed that the line was hypotetraploid, with a mean chromosome number of 73. None of the 50 karyotyped cells had a normal chromosome #1 or Y. Cells with multiple copies of some of the autosomes were observed frequently. Structural rearrangements were numerous, especially of chromosomes #1, #9, #14, X, and Y.

Aneuploidy↗
PubMed1986

Characteristics and distribution of beta thalassemia haplotypes in South China.

Eleven restriction site polymorphisms in the beta-globin gene cluster were determined in 48 Chinese with homozygous beta-thalassemia and their parents. Seven haplotypes were identified as associated with the beta thal chromosome and 25 with the beta A chromosome. The distribution of the various beta thal haplotypes in different regions of South China was mapped and discussed in relation to prenatal diagnosis and migration of the Chinese people.

China↗
PubMed1986

Organization of the zeta-alpha genes in Chinese.

Analysis of alpha and zeta genes in 101 healthy normals and hospitalized patients with non-haematological diseases revealed a 3% incidence of alpha thalassaemia in the local Chinese population of Hong Kong. Triple alpha genes were found in only one person while triple zeta genes were more prevalent, occurring in 13 subjects. Studies of 28 unselected patients with Hb H disease indicated a predominance of the rightward alpha gene deletion. The extent of alpha gene deletion in homozygous alpha thalassaemia 1 was at least 18.1 kb, beginning from the BamH I site 3' to the zeta 1 gene and includes the psi alpha, alpha 2 and alpha 1 genes. Nineteen of the 20 chromosomes bearing the alpha thalassaemia 1 deletion had identical zeta-intergenic hypervariable region suggesting a common origin of this mutation. The co-inheritance of alpha thalassaemia in beta thalassaemia subjects was 8%, but did not ameliorate the clinical features of those with homozygous beta thalassaemia.

China↗
PubMed1972

[Two decades].

Explore the source record for details and available documents.

Child Development↗
PubMedDate not supplied

Back pain and vertebral compression: an uncommon presentation of childhood acute lymphoblastic leukemia.

Acute lymphoblastic leukemia (ALL) presenting with bone pain and leukopenia is a recognized clinicopathological complex. Three patients with ALL presented with back pain as the major symptom. These cases, together with those previously described in the literature, illustrate that delay in diagnosis frequently occurs, with the classic features of the disease being uniformly absent. The reasons for the etiology of the bone pain in ALL are in dispute. It would appear, however, that if early diagnosis can be made, then prognosis is not impaired.

Acute Disease↗