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Biomedical subjects

J Leong

Publications and source records attributed to J Leong.

At least 55 records · Page 3Linked to original sources
PubMed1984

What's so special about special care?

Special care units are the most advanced, intensive, technological, and costly of hospital services. They also have proliferated rapidly. Yet little is understood about the definition, prevalence, genesis, costs, or benefits of SCUs. This paper defines and examines the many forces that have promoted the growth of special care, including hospital cost containment policies, fee-for-service reimbursement, medical ethics, standards of care, and manpower, and the much less numerous forces that have inhibited its spread. It is concluded that a sound appreciation of the dynamics of SCUs will be crucial to guiding future policy decisions as the nation's population ages and as hospitals continue to improve their capability to care for critically ill patients.

Attitude of Health Personnel↗
PubMed1982

An improved method for preparation of semen for artificial insemination by husband.

An improved method of semen preparation for artificial insemination, which involves filtration on an albumin column followed by resuspension in fasting blood serum, is described. The proportion of motile sperms, the quality of motility, motility index, and life span of the sperms in vitro are improved. Six pregnancies have resulted from the use of this method.

Female↗
PubMed1982

Production of deferriferrioxamines B and E from a ferroverdin-producing Streptomyces species.

When Streptomyces sp. strain Wak. A-305 is cultured in iron (III)- or cobalt (II)-containing media, tris(p-vinylphenyl-4-hydroxy-3-nitrosobenzoato-N3, O4)ferrate(II) (ferroverdin) or the analogous tris-cobalt(III) complex, respectively, is produced intracellularly. In contrast, when cultured in transition metal ion-limiting media. Streptomyces sp. strain Wak. A-305 did not produce p-vinylphenyl 4-hydroxy-3-nitrosobenzoate (deferroferroverdin). Instead, deferriferrioxamines B and E, which have been characterized from other streptomycetes, were isolated extracellularly and may act as siderophores in this organism.U

Chlorides↗
PubMed1981

Structure of ferric pseudobactin, a siderophore from a plant growth promoting Pseudomonas.

Both plant growth promoting Pseudomonas B10 and its yellow-green, fluorescent iron transfer agent (siderophore) pseudobactin enhance the growth of the potato and control certain phytopathogenic microorganisms. The structure of the little compound has been determined by single-crystal X-ray diffraction methods using counter data. The structure consisted of a linear hexapeptide, L-Lys-D-threo-beta-OH-Asp-L-Ala-D-allo-Thr-L-Ala-D-N delta-OH-Orn, in which the N delta-OH nitrogen of the ornithine was cyclized with the C-terminal carboxyl group, and the N epsilon-amino group of the lysine was linked via an amide bond to a fluorescent quinoline derivative. The iron-chelating groups consisted of a hydroxamate group derived from N delta-hydroxyornithine, an alpha-hydroxy acid derived from beta-hydroxyaspartic acid, and an o-dihydroxy aromatic group derived from the quinoline moiety. The combination of metal-chelating ligands and the alternating L- and D-amino acids was unusual. The little compound crystallized as a single coordination isomer with the lambda absolute configuration. The present study is the first structural determination of a fluorescent siderophore. In the crystal structure, ferric pseudobactin formed a dimer, which constituted the asymmetric unit. The asymmetric unit also contained 26 water molecules. The molecules in the dimer were related by a pseudo-2-fold symmetry axis. Red-brown crystals of ferric pseudobactin (C42H57N12O16Fe . 13H2O), obtained from pyridine-acetic acid buffer solution equilibrated with water, conformed to space group I2 with a = 29.006 (23) A, b = 14.511 (13) A, c = 28.791 (21) A, and beta = 96.06 (5) degrees at -135 (2) degrees C. For eight molecules per unit cell, the calculated density was 1.38 g/cm3; the observed density was 1.40 g/cm3. The structure was refined by least-squares methods with anisotropic thermal parameters for all nonhydrogen atoms to a final R factor of 0.08 (8989 observed reflections).

Amino Acid Sequence↗
PubMed1981

Structure of pseudobactin A, a second siderophore from plant growth promoting Pseudomonas B10.

The structure of nonfluorescent pseudobactin A, one of two extracellular siderophores (microbial iron transport agents) produced by the plant growth promoting bacterium Pseudomonas B10, was determined by comparison of its 1H and 13C NMR spectra with those of yellow-green, fluorescent pseudobactin, the other siderophore. The molecular and crystal structure of ferric pseudobactin is reported in the preceding paper in this issue [Teintze, M., Hossain, M. B., Barnes, C. L., Leong J., & van der Helm, D. (1981) Biochemistry (preceding paper in this issue)]. The only structural difference between pseudobactin and pseudobactin A was that the latter was saturated at carbons 3 and 4 of the quinoline derivative, whereas pseudobactin is unsaturated at these positions. A mechanism is proposed for the observed conversion of pseudobactin A into pseudobactin in aqueous solution.

Amino Acid Sequence↗
PubMed1981

Mode of antibiotic action of 4-hydroxy-3-nitrosobenzaldehyde from Streptomyces viridans.

The free ligand, deferroviridomycin A, and its iron(II) complex, viridomycin A, were detected in culture supernatant fluids of Streptomyces viridans 1671 and were structurally characterized as 4-hydroxy-3-nitrosobenzaldehyde and tris(4-hydroxy-3-nitrosobenzaldehydato-N3,O4)ferrate(II), respectively. We investigated the antibiotic activity of the above compounds and of the chemically synthesized bis copper(II), tris cobalt(III), and tris nickel(II) complexes against Escherichia coli NIHJ, Salmonella typhimurium LT-2Z, Staphylococcus aureus 209P, Streptococcus faecium 10541, and Bacillus cereus, T. The free ligand and its kinetically labile copper(II) and nickel(II) complexes displayed activity against all of the above organisms, whereas the kinetically inert iron(II) and cobalt(III) complexes displayed activity only against S. aureus and B. cereus. The antibiotic activity of the substitutionally labile metal complexes was attributed to dissociation of the free ligand. The mode of antibiotic action of the free ligand against E. coli appears to be interference with the structural and functional integrity of the cell membrane.

Bacillus cereus↗
PubMed1980

Refluxing ureteroceles.

We report 4 cases of 3 different forms of ureteroceles to illustrate spontaneous reflux without any evidence of obstruction. The presence of reflux tends to support those concepts that ureterocele formation is not on an obstructive basis. The obstruction that is oftern associated with ureteroceles is probably caused by the same stimulus as that which created the ureterocele. Obstruction does not necessarily accompany every ureterocele and is not causative of its formation.

Adolescent↗
PubMed1980

Inactivation of poliovirus I (Brunhilde) single particles by chlorine in water.

Like the Mahoney strain, the Brunhilde strain of poliovirus aggregated slowly in dilute phosphate-carbonate buffer at pH 6 but not at all at or above pH 7. Infectivity decreased at rates approximately proportional to the concentration of free chlorine present at pH 6 over the entire range of 5 to 40 micrometer. The addition of 0.1 M NaCl to the buffer increased the rate about twofold, but this strain was still twice as resistant as the Mahoney strain. At pH 10, inactivation was much slower than at pH 6, but when 0.1 M NaCl was added, the rate was increased 31-fold, making the OCl- at pH 10 over three times more effective than HOCl at pH 6.

Buffers↗
PubMed1979

Antibiotic action of N-methylthioformohydroxamate metal complexes.

The antibiotic activity of metal complexes of N-methylthioformohydroxamic acid against gram-negative Escherichia coli NIHJ and gram-positive Staphylococcus aureus 209P was investigated. The kinetically labile, square-planar, divalent (Cu, Ni, and Pd) and octahedral, trivalent (Fe, Co, and Cr) complexes displayed activity, whereas the more inert platinum(II) or rhodium(III) complex displayed no activity, or activity only at elevated concentrations. The free ligand did not suppress the growth of the above organisms, and the sulfur atom of the ligand in its metal complexes appears crucial for activity. Uptake studies of radioactively labeled N-methylthioformohydroxamic acid, its nickel(II), platinum(II), iron(III), and rhodium(III) complexes were conducted in the Escherichia coli K-12 RW193 mutant, which is defective in the production of its native iron(III) transport agent, enterobactin. Uptake of (55)Fe or (63)Ni label from their metal complexes appeared to occur as free inorganic metal ions. The antibiotic activity of the iron(III) and nickel(II) complexes was not due merely to an enhanced accumulation of metal ions by the cell. Metal complexes of [(35)S]N-methylthioformohydroxamic acid enhanced the accumulation of (35)S label compared to that of the free ligand. The antibiotic activity and uptake data are discussed in terms of possible modes of action.

Anti-Bacterial Agents↗
PubMed1976

Mechanisms of siderophore iron transport in enteric bacteria.

Uptake of 55Fe- and 3H-labeled siderophores and their chronic analogues have been studied in Salmonella typhimurium LT-2 and Escherichia coli K-12. In S. typhimurium LT-2, at least two different mechanisms for siderophore iron transport may be operative. Uptake of 55Fe- and 3H-labeled ferrichrome and kinetically inert lambda-cis-chromic [3H]deferriferrichrome by the S. typhimurium LT-2 enb7 mutant, which is defective in the production of its native siderophore, enterobactin, appears to occur by two concurrent mechanisms. The first mechanism is postulated to involve either rapid uptake of iron released from the ferric complex by cellular reduction without penetration of the complex or ligand or dissociation of the complex and simultaneous uptake of both ligand and iron coupled with simultaneous expulsion of the ligand. The second mechanism appears to consist of slower uptake of the intact ferric complex.

Biological Transport, Active↗
PubMedDate not supplied

Human mast cell proteases hydrolyze neurotensin, kinetensin and Leu5-enkephalin.

Purified mast cell carboxypeptidase cleaved the C-terminal leucines from Leu5-enkephalin (Leu-ENK), neurotensin (NT), and kinetensin (KT), with Km values of 36, 16, and 15 microM, and kcat values of 44, 51, and 53 s-1, respectively. To better predict potential in vivo hydrolysis products generated by mast cell proteases, these peptides were incubated with released skin mast cell supernatants. Leu5-enkephalin was hydrolyzed only by carboxypeptidase. Kinetensin was cleaved by tryptase, chymase, and carboxypeptidase to yield KT(1-3), KT(1-7), KT(1-8), KT(4-7), and KT(4-8), the last two peptides by the concerted action of two of the proteases. NT(1-11) and NT(1-12) were generated from neurotensin by chymase and carboxypeptidase, respectively.

Amino Acid Sequence↗