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Biomedical subjects

H Ma

Publications and source records attributed to H Ma.

At least 307 records · Page 17Linked to original sources
PubMed1989

Isolation and characterization of mutations in the HXK2 gene of Saccharomyces cerevisiae.

Several hundred new mutations in the gene (HXK2) encoding hexokinase II of Saccharomyces cerevisiae were isolated, and a subset of them was mapped, resulting in a fine-structure genetic map. Among the mutations that were sequenced, 35 were independent missense mutations. The mutations were obtained by mutagenesis of cloned HXK2 DNA carried on a low-copy-number plasmid vector and screened for a number of different phenotypes in yeast strains bearing chromosomal hxk1 and hxk2 null mutations. Some of these mutants were characterized both in vivo and in vitro; they displayed a wide spectrum of residual hexokinase activities, as indicated by three assays: in vitro enzyme activity, ability to grow on glucose and fructose, and ability to repress invertase production when growing on glucose. Of those that failed to support growth on fructose, only a small minority made normal-size, stable, and inactive protein. Analysis of the amino acid changes in these mutants in light of the crystallographically determined three-dimensional structure of hexokinase II suggests important roles in structure or catalysis for six amino acid residues, only two of which are near the active site.

Amino Acids↗
PubMed1989

The residual enzymatic phosphorylation activity of hexokinase II mutants is correlated with glucose repression in Saccharomyces cerevisiae.

Saccharomyces cerevisiae mutants containing different point mutations in the HXK2 gene were used to study the relationship between phosphorylation by hexokinase II and glucose repression in yeast cells. Mutants showing different levels of hexokinase activity were examined for the degree of glucose repression as indicated by the levels of invertase activity. The levels of hexokinase activity and invertase activity showed a strong inverse correlation, with a few exceptions attributable to very unstable hexokinase II proteins. The in vivo hexokinase II activity was determined by measuring growth rates, using fructose as a carbon source. This in vivo hexokinase II activity was similarly inversely correlated with invertase activity. Several hxk2 alleles were transferred to multicopy plasmids to study the effects of increasing the amounts of mutant proteins. The cells that contained the multicopy plasmids exhibited less invertase and more hexokinase activity, further strengthening the correlation. These results strongly support the hypothesis that the phosphorylation activity of hexokinase II is correlated with glucose repression.

Alleles↗
PubMed1987

Plasmid construction by homologous recombination in yeast.

We describe a convenient method for constructing new plasmids that relies on interchanging parts of plasmids by homologous recombination in Saccharomyces cerevisiae. A circular recombinant plasmid of a desired structure is regenerated after transformation of yeast with a linearized plasmid and a DNA restriction fragment containing appropriate homology to serve as a substrate for recombinational repair. The free ends of the input DNA molecules need not be homologous in order for efficient recombination between internal homologous regions to occur. The method is particularly useful for incorporating into or removing from plasmids selectable markers, centromere or replication elements, or particular alleles of a gene of interest. Plasmids constructed in yeast can subsequently be recovered in an Escherichia coli host. Using this method, we have constructed an extended series of new yeast centromere, episomal and replicating (YCp, YEp, and YRp) plasmids containing, in various combinations, the selectable yeast markers LEU2, HIS3, LYS2, URA3 and TRP1.

Alleles↗
PubMed1987

Fine structure recombinational analysis of cloned genes using yeast transformation.

We describe a general method for analyzing the genetic fine structure of plasmid-borne genes in yeast. Previously we had reported that a linearized plasmid is efficiently rescued by recombination with a homologous restriction fragment when these are co-introduced by DNA-mediated transformation of yeast. Here, we show that a mutation can be localized to a small DNA interval when members of a deletion series of wild-type restriction fragments are used in the rescue of a linearized mutant plasmid. The resolution of this method is to at least 30 base pairs and is limited by the loss of a wild-type marker with proximity to a free DNA end. As a means for establishing the nonidentity of two mutations, we determined the resolution of two-point crosses with a mutant linearized plasmid and a mutant homologous restriction fragment. Recombination between mutations separated by as little as 100 base pairs was detected. Moreover, the results indicate that exchange within a marked interval results primarily from one of two single crossovers that repair the linearized plasmid. These approaches to mapping the genetic fine structure of plasmids should join existing methods in a robust approach to the mutational analysis of gene structure in yeast.

Chromosome Deletion↗
PubMed1986

Effects of null mutations in the hexokinase genes of Saccharomyces cerevisiae on catabolite repression.

Saccharomyces cerevisiae has two homologous hexokinases, I and II; they are 78% identical at the amino acid level. Either enzyme allows yeast cells to ferment fructose. Mutant strains without any hexokinase can still grow on glucose by using a third enzyme, glucokinase. Hexokinase II has been implicated in the control of catabolite repression in yeasts. We constructed null mutations in both hexokinase genes, HXK1 and HXK2, and studied their effect on the fermentation of fructose and on catabolite repression of three different genes in yeasts: SUC2, CYC1, and GAL10. The results indicate that hxk1 or hxk2 single null mutants can ferment fructose but that hxk1 hxk2 double mutants cannot. The hxk2 single mutant, as well as the double mutant, failed to show catabolite repression in all three systems, while the hxk1 null mutation had little or no effect on catabolite repression.

Enzyme Repression↗
PubMed1985

Metabolic effects of manganese deficiency in Aspergillus niger: evidence for increased protein degradation.

The effect of manganese deficiency on macromolecule synthesis has been studied in a citric acid producing strain of Aspergillus niger: pulse labelling experiments showed that the synthesis of both protein and RNA was not influenced by the presence of manganese; however, increased protein degradation occurred under manganese deficiency. This was also reflected by the increased activity of an intracellular proteinase activity under these conditions. In replacement cultures addition of inhibitors of RNA, DNA or protein synthesis revealed that only emetine and cycloheximide (which both act at the ribosome) successfully antagonized the adverse effect of manganese ions on citric acid accumulation. Manganese deficiency was also characterized by a decreased portion of polysomes and 80 S ribosomes.

Aspergillus niger↗
PubMed1984

New sequential external counterpulsation for the treatment of acute myocardial infarction.

Over a period of 6 years, 52 patients with acute myocardial infarction (AMI) were treated with sequenced external counterpulsation (SECP). Of the 23 patients who experienced severe chest pain, 22 had complete relief within 30 min of SECP, and 31 of the 52 patients showed remarkable improvement in their electrocardiogram after the first hour of treatment. Fifteen patients were studied using the 35-lead ST segment elevation-mapping method. sigma ST and NST, indicators of infarct size, showed decreasing trends in seven patients treated with SECP for a period of 6 days, whereas sigma ST and NST of the control group of eight patients increased during the same period. Our hemodynamic data indicate that in four of five patients with AMI and left heart failure, the central venous pressure and cardiac output increased after SECP, whereas the pulmonary wedge pressure decreased. Measurements of the P-wave terminal force of lead V1 also demonstrated that the application of SECP can improve left ventricular function in a majority of patients with AMI.

Adult↗
PubMed1982

Formation of halide-ions on one-electron reduction of halogenated nitroimidazoles in aqueous solution. A radiolytic study.

Reactions of e-aq, (CH3)2COH and CO.2- with a series of halogenated nitroimidazoles (ArNO2) results predominantly in the formation of their one-electron reduced species (ArNO.2-), the properties of which are consistent with those of other nitroimidazole radical anions. Further, one-electron reduction of ArNO2 ultimately leads to production of halide ion (X-); G(X-) = 1.2 to 2.2. In the presence of either the nitroxyl free radical, norpseudopelletierine-N-oxyl (NPPN), or oxygen the yield of X- is reduced and 'residual' yields of X- were observed, G(X-) = 0.08 to 0.43. From the results it is suggested that less than or equal to 10 per cent of the yield of reducing species results in the production of X- and an imidazolyl-type radical and that the majority of the yield of X- results from subsequent reactions of ArNO.2- (e.g. bimolecular reactions).

Halogens↗
PubMedDate not supplied

Purification and characterization of hedgehog liver metallothioneins.

Two forms of liver metallothioneins (MTs) were purified from hedgehog exposed to zinc, using gel filtration on Sephacryl S-100 and DEAE Sepharose Fast Flow chromatography. The peptide chain weight of both MT-1 and MT-2 was found to be about 10,000, as determined by high performance liquid chromatography. This value was higher than that calculated from amino acid analysis. The amino acid composition of hedgehog liver MT-1 and MT-2 resembles that of liver to MTs from rabbit and other species. Their distinctive features include an extremely high cysteine content, about 33% of all the amino acid residues, and an absence of aromatic amino acids and histidine. In addition, a rapid method for the determination of MTs during animal tissue purification has been established. The samples were directly added in an ammoniacal solution of a Co(II) salt for recording linear sweep polarograms. By comparison with the commonly used metal determination method, our method is direct, rapid, credible and suitable for all the MTs or MT-like samples.

Amino Acids↗
PubMedDate not supplied

Pharmacologic treatment of otitis media and sinusitis in pediatrics.

Otitis media and sinusitis are common diseases of childhood whose treatment is essential to long-term health. This article presents an update on the microorganisms involved in these two conditions and the selection and appropriate use of antimicrobial drugs for treatment. The issues of prophylaxis of recurrent otitis media and potential vaccines are discussed. In addition, approaches to increase patient compliance are presented, and the role of the nurse in educating parents about the condition and its treatment is discussed.

Anti-Bacterial Agents↗