Biomedical subjects

G M Lazarus

Publications and source records attributed to G M Lazarus.

11 recordsLinked to original sources

PubMed2001

Gender-specific medicine in pediatrics.

As pediatricians have always known, boys and girls are different. Many pediatric diseases and syndromes are either more common or more severe in one sex than in the other. Puberty brings about emotional and physical changes that are obviously very different in males and females. In addition, certain "adult" conditions with gender differences, such as osteoporosis and long QT syndrome, may be present or preventable in the early years. Physicians should strive to understand these differences so that they can tailor medicine and other therapies to specifically meet the needs of each gender.

Disease↗

PubMed1992

DNA topoisomerase I from calf thymus mitochondria is associated with a DNA binding, inner membrane protein.

During purification of the type I DNA topoisomerase from calf thymus mitochondria, two polypeptides, p78 and p63, cofractionate with the enzymatic activity (Lazarus et al., (1987) Biochemistry 26, 6195-6203). The two polypeptides are released from a mitochondrial inner membrane preparation by nonionic detergent lysis and both adsorb strongly to a single-stranded DNA agarose column. We have attempted to characterize the relationship between these two polypeptides and have found the following: (i) the mitochondrial topoisomerase is active in free (monomer) and associated (heterodimer) form; (ii) the catalytic activity resides solely in p78, as adjudged by both the covalent linkage of the enzyme to substrate DNA and the ability of the enzyme to relax supercoils; (iii) at low ionic strength the enzyme is active in monomer form with p78 alone being sufficient for activity; (iv) in high salt, the high molecular weight species is a 140-kDa heterodimer composed of one p78 and one p63; and (v) the two polypeptides are not structurally related as digestion with V8 protease results in distinct proteolytic fragment patterns. These results suggest that p63 may have an important role in the metabolism of the mitochondrial topoisomerase.

Animals↗

PubMed1989

Recombinant HIV-1 reverse transcriptase: purification, primary structure, and polymerase/ribonuclease H activities.

Recombinant HIV-1 reverse transcriptase (RT) was stably overproduced as a soluble protein in Escherichia coli using a double-plasmid expression system in which an RT precursor protein was expressed and processed in vivo by HIV-1 protease produced in trans. The RT thus produced consisted of an equimolar mixture of two polypeptides, p66 and p51, which were copurified to greater than 90% homogeneity and were found to share a common NH2 terminus as judged by sequence analysis of the polypeptide mixture. The observed sequence confirmed correct in vivo cleavage by protease at the protease-RT polyprotein junction to yield an NH2 terminus identical to that of genuine viral RT (M. M. Lightfoote et al. (1986) J. Virol. 60, 771-775; F. diMarzo Veronese et al. (1986) Science 231, 1289-1291). The bacterially expressed RT had a specific activity similar to that of viral RT and inhibition studies with phosphonoformate confirmed that it was indistinguishable from the viral enzyme with respect to sensitivity to this inhibitor. Polymerase activated gel analysis of the mixture indicated that p66 was associated with a higher level of RT activity than p51. RNase H activated gel analysis suggested that the purified preparation of recombinant RT was free of endogenous E. coli RNase H, and that the RNase H activity of RT was exclusively associated with the p66 polypeptide, supporting the hypothesis that the RNase H domain is located in the COOH-terminal region of the molecule.

Amino Acids↗

PubMed1987

Purification and characterization of a type I DNA topoisomerase from calf thymus mitochondria.

A type I topoisomerase has been purified more than 4000-fold from calf thymus mitochondria. The enzyme is membrane associated and is effectively solubilized by 1% Triton X-100 treatment of purified mitochondrial inner membranes. This ATP-independent enzyme relaxes positively and negatively supercoiled DNA with delta LK = 1. At low ionic strength, the native enzyme appears to be a monomer (sedimentation coefficient of 4.3 S and Stokes radius of 34 A), but it can form a weakly associated dimer at higher salt concentrations (sedimentation coefficient of 7.0 S and Stokes radius of 47.5 A). The mitochondrial type I topoisomerase is distinguishable from the nuclear enzyme by its (1) pH profile, (2) thermal stability, (3) response to dimethyl sulfoxide and Berenil, and (4) molecular weight. The mitochondrial enzyme is inhibited by elevated concentrations of the bacterial DNA gyrase inhibitor novobiocin, but not nalidixic or oxolinic acids. Sensitivity to N-ethylmaleimide indicates the importance of cysteine for catalytic activity. It is estimated that there are at least five copies of topoisomerase I per mammalian mitochondrion or a minimum of one to two per mitochondrial genome. In a manner similar to that observed with leukemia (nuclear and mitochondrial), calf thymus (nuclear), and HeLa (nuclear) cell type I topoisomerase, the calf thymus mitochondrial enzyme is inhibited by physiological concentrations of ATP.

Animals↗

PubMed1985

The presence of two mitochondrial DNA topoisomerases in human acute leukemia cells.

We have undertaken a study of DNA topoisomerases in mitochondria from human acute leukemia cells. Two activities have been detected in these organelles. One of the enzymes is presumably a type II topoisomerase, i.e., in ATP-dependent reactions it can catenate closed circular plasmid DNA, and decatenate closed circular kinetoplast DNA. A second topoisomerase is presumably a type I enzyme since, it can relax positive as well as negative supercoils in an ATP-independent reaction, it is unable to catenate plasmid DNA or decatenate kinetoplast DNA, and it is inhibited, rather than stimulated, by ATP.

Acute Disease↗

PubMed1984

Isolation of a mitochondrial DNA topoisomerase from human leukemia cells.

Mitochondria from human acute lymphoblastic leukemia cells contain an ATP-independent DNA topoisomerase which can relax negative and positive supercoils. This enzyme has been purified 200-fold by carboxymethyl-cellulose or double stranded DNA-cellulose chromatography. In contrast to the molecular weights reported for mitochondrial topoisomerases in other systems, the native leukemia enzyme has a molecular weight of 132,000 daltons as determined by gel permeation chromatography in buffer containing 0.4 M KC1. It also exhibits a sedimentation coefficient of 7.1 S when centrifuged through a 10-30% glycerol gradient in this high salt buffer. The enzyme is presumably a type I topoisomerase analogous to those found in rat liver and Xenopus laevis mitochondria.

Chromatography↗

PubMed1979