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Biomedical subjects

C Walsh

Publications and source records attributed to C Walsh.

At least 163 records · Page 9Linked to original sources
PubMed1986

Cytochrome P-450 isozymes from the marine teleost Stenotomus chrysops: their roles in steroid hydroxylation and the influence of cytochrome b5.

Two new cytochrome P-450 forms were purified from liver microsomes of the marine fish Stenotomus chrysops (scup). Cytochrome P-450A (Mr = 52.5K) had a CO-ligated, reduced difference spectrum lambda max at 447.5 nm, and reconstituted modest benzo[a]pyrene hydroxylase activity (0.16 nmol/min/nmol P-450) and ethoxycoumarin O-deethylase activity (0.42 nmol/min/nmol P-450). Cytochrome P-450A reconstituted under optimal conditions catalyzed hydroxylation of testosterone almost exclusively at the 6 beta position (0.8 nmol/min/nmol P-450) and also catalyzed 2-hydroxylation of estradiol. Cytochrome P-450A is active toward steroid substrates and we propose that it is a major contributor to microsomal testosterone 6 beta-hydroxylase activity. Cytochrome P-450A had a requirement for conspecific (scup) NADPH-cytochrome P-450 reductase and all reconstituted activities examined were stimulated by the addition of purified scup cytochrome b5. Cytochrome P-450B (Mr = 45.9K) had a CO-ligated, reduced difference spectrum lambda max at 449.5 nm and displayed low rates of reconstituted catalytic activities. However, cytochrome P-450B oxidized testosterone at several different sites including the 15 alpha position (0.07 nmol/min/nmol P-450). Both cytochromes P-450A and P-450B were distinct from the major benzo[a]pyrene hydroxylating form, cytochrome P-450E, by the criteria of spectroscopic properties, substrate profiles, minimum molecular weights on NaDodSO4-polyacrylamide gels, peptide mapping and lack of cross-reaction with antibody raised against cytochrome P-450E. Cytochrome P-450E shares epitopes with rat cytochrome P-450c indicating it is the equivalent enzyme, but possible homology between scup cytochromes P-450A or P-450B and known P-450 isozymes in other vertebrate groups is uncertain, although functional analogs exist.

Animals↗
PubMed1986

Age-related fiber order in the ferret's optic nerve and optic chiasm.

Although the mammalian optic tract shows a grouping of fibers by age, with newer fibers nearer the pial surface, the possible rules for fiber ordering in the mammalian optic nerve have not been well defined. In this study, preferential labeling of the older retinal fibers in the ferret, a close relative of the cat, shows that the age-related fiber order in the ferret's optic tract reflects a systematic sorting of fibers by age that occurs in the optic nerve, and that is maintained through the optic chiasm. The older retinofugal fibers, dispersed throughout the nerve near the retina, come to be limited to the perimeter of the nerve as it passes through the optic foramen, while newer fibers come to lie nearest the center of the nerve. These newest fibers approach the ventral surface of the brain nearer the optic chiasm. In the chiasm, as in the tract, the oldest fibers lie furthest from the pial surface of the brain, while newer fibers lie nearer the surface. The age-related fiber ordering in the ferret's optic nerve, with the newest fibers initially being furthest from the surface at the optic foramen, differs from age-related orderings seen in nonmammalian vertebrates, where the newest fibers are always nearest the surface. The changing patterns of fiber ordering along the ferret's optic nerve may relate to changes in the underlying glial structure of the developing nerve.

Age Factors↗
PubMed1985

Factor 390 chromophores: phosphodiester between AMP or GMP and methanogen factor 420.

Two chromophores with absorbance maxima at 390 nm (factors 390) have been isolated from oxidized cells of Methanobacterium thermoautotrophicum delta H. The isolation procedure included anion-exchange chromatography of the soluble cofactor pool followed by reverse-phase chromatography. The factor 390 species are novel derivatives of methanogen coenzyme factor 420 in which the 5-deazaflavin 8-hydroxy group is in a phosphodiester linkage to adenosine 5'-phosphate or guanosine 5'-phosphate. The structural assignments were based, in part, on the UV-visible and 1H NMR spectra. In addition, the results from amino acid analysis, phosphate determination, 31P NMR spectroscopy, and fast atom bombardment mass spectrometry were consistent with the proposed structures. Confirmation of the factor 390 structures was made following phosphodiesterase release of the nucleotide monophosphates from factor 420. The nucleotide monophosphates were identified as AMP and GMP by UV-visible spectra and based on elution position by using reverse-phase and anion-exchange high-performance liquid chromatography. The presence of AMP was further demonstrated by using adenylate-5'-phosphate kinase which induced a spectral shift during conversion of the sample to IMP. In addition, the presence of GMP was established by a specific enzymatic assay.

Adenosine Monophosphate↗
PubMed1985

Purification of an alanine racemase from Streptococcus faecalis and analysis of its inactivation by (1-aminoethyl)phosphonic acid enantiomers.

An alanine racemase has been purified some 30 000-fold almost to homogeneity from Gram-positive Streptococcus faecalis NCIB 6459; the enzyme has been purified to the same extent (4000-fold) from an O-carbamyl-D-serine-resistant mutant with a 7-fold higher enzyme level in crude extract. The racemase has one pyridoxal phosphate molecule per 42-kDa subunit, has a Vmax of 3570 units/mg and a Km of 7.8 mM in the L to D direction, and has a Vmax of 1210 units/mg and a Km of 2.2 mM in the D to L direction. The Keq is 0.8 and kcat/Km values are ca. 3 X 10(5) M-1 s-1. The purified enzyme is inhibited in a time-dependent manner by both L- and D-(l-aminoethyl)phosphonates (Ala-P), confirming observations of Atherton et al. in crude extracts of this organism [Atherton, F. R., Hall, M. J., Hassal, C. H., Holmes, S. W., Lambert, R. W., Lloyd, W. J., & Ringrose, P. S. (1980) Antimicrob. Agents Chemother. 18, 897]. Studies with [1-2H]-, [1-3H]-, and [1,2-14C]Ala-P rule out enzymic activation and processing as the basis for irreversible inhibition. Thus, enzyme after exposure to [14C]Ala-P or [alpha-3H]Ala-P and gel filtration contains stoichiometric amounts of radioactive label, but denaturation quantitatively releases intact Ala-P into solution as revealed by high-performance liquid chromatography and cocrystallization with authentic material. The Ala-P isomers are slow binding inhibitors of this racemase as is the alpha,alpha'-dimethyl analogue but not the D or L isomers of the corresponding phosphinate.(ABSTRACT TRUNCATED AT 250 WORDS)

Alanine Racemase↗
PubMed1985

Thrombocytopenia in homosexual patients. Prognosis, response to therapy, and prevalence of antibody to the retrovirus associated with the acquired immunodeficiency syndrome.

Thirty-three homosexual patients with thrombocytopenia (mean [+/- SE] platelet count, 50 000 +/- 7000/mm3; range, 7 to 135 000/mm3) have been followed for a mean period of 20 +/- 2 months. Six patients have developed the acquired immunodeficiency syndrome 1 to 37 months after the diagnosis of thrombocytopenia. Six patients spontaneously reverted to normal platelet counts 5 to 27 months (median, 10 months) after the diagnosis of thrombocytopenia, in the absence of splenectomy and while not receiving corticosteroids. Sixteen of seventeen patients had a moderate to excellent response while on corticosteroid treatment. Ten of ten patients had an excellent response to splenectomy which has persisted. Fifteen patients did not require treatment for their thrombocytopenia. Thirteen of fourteen patients had antibody against the retrovirus associated with the acquired immunodeficiency syndrome, as did 4 of 12 homosexual controls without thrombocytopenia. Thrombocytopenia in homosexuals is part of the complex related to the acquired immunodeficiency syndrome.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Age-related fiber order in the optic tract of the ferret.

In the ferret's optic tract, the position of retinofugal fibers has been related to their relative age by preferentially labeling the oldest fibers. It has been found that fiber order perpendicular to the pial surface represents the sequence of axon arrivals in the optic tract, the fibers furthest from the pia being the oldest. Immature ferrets, less than 34 days post-conception (E34), were given intravitreal injections of lectin-bound horseradish peroxidase or of 3H-amino acids. After survival times of 24 hr or less, the contralateral optic tract was uniformly labeled, whereas with longer survival times unlabeled zones were seen next to the pial border. These unlabeled zones were largest after injections into the youngest animals but were never seen when injections were made after E34, no matter what the survival time. The unlabeled zones were seen in the tracts of animals having unlabeled regions in the periphery of the retina. The unlabeled retinal ganglion cells are interpreted as ganglion cells formed after the injection was made, and unlabeled axons next to the pia in the tract are interpreted as the axons of these youngest cells. Some irregularities in the layered arrangement of the tract are described, and the fiber order in the tract is contrasted with that in the optic nerve behind the eye. It is shown that tract order is partially independent of order in the intraorbital part of the optic nerve. Between the retina and the optic tract, a sorting of fibers occurs not only in terms of the pattern of decussation, but also in terms of fiber age.

Aging↗
PubMed1985

The topography of ganglion cell production in the cat's retina.

The ganglion cells of the cat's retina form several classes distinguishable in terms of soma size, axon diameter, dendritic morphology, physiological properties, and central connections. Labeling with [3H]thymidine shows that the ganglion cells which survive in the adult are produced as several temporally shifted, overlapping waves: medium-sized cells are produced before large cells, whereas the smallest ganglion cells are produced throughout the period of ganglion cell generation (Walsh, C., E. H. Polley, T. L. Hickey, and R. W. Guillery (1983) Nature 302: 611-614). Large cells and medium-sized cells show the same distinctive pattern of production, forming rough spirals around the area centralis. The oldest cells tend to lie superior and nasal to the area centralis, whereas cells in the inferior nasal retina and inferior temporal retina are, in general, progressively younger. Within each retinal quadrant, cells nearer the area centralis tend to be older than cells in the periphery, but there is substantial overlap. The retinal raphe divides the superior temporal quadrant into two zones with different patterns of cell addition. Superior temporal retina near the vertical meridian adds cells only slightly later than superior nasal retina, whereas superior temporal retina near the horizontal meridian adds cells very late, contemporaneously with inferior temporal retina. The broader wave of production of smaller ganglion cells seems to follow this same spiral pattern at its beginning and end. The presence of the area centralis as a nodal point about which ganglion cell production in the retinal quadrants pivots suggests that the area centralis is already an important retinal landmark even at the earliest stages of retinal development. This sequence of ganglion cell production differs markedly from that seen in the retinae of nonmammalian vertebrates, where new ganglion cells are added as concentric rings to the retinal periphery, and also bears no simple relationship to the cat's retinal decussation line. However, it can be related in a straightforward manner to the organization of axons in the cat's optic tract, suggesting that the fiber order in the tract represents a grouping of fibers by age.

Animals↗
PubMed1984

An alternative 7-ethoxyresorufin O-deethylase activity assay: a continuous visible spectrophotometric method for measurement of cytochrome P-450 monooxygenase activity.

A procedure to directly measure the cytochrome P-450-dependent 7-ethoxyresorufin O-deethylase activity with a visible spectrophotometer is described and compared to the standard fluorometric method. The two assays yielded identical results with both beta-naphthoflavone-treated mammalian (rat) and fish (scup, Stenotomus chrysops) liver microsomes. The assay takes advantage of a clean distinction in visible absorption spectra obtained for highly purified 7-ethoxyresorufin (substrate) and resorufin (enzymatic product). The purification and characterization of resorufin, the enzymatic product, are detailed, and its extinction coefficient (epsilon 572 = 73 mM-1 cm-1) provides for an accurate quantitation of enzyme activity. The large visible extinction coefficient of the product chromophore provides a high sensitivity for low-activity samples. The application of this enzyme assay in a visible spectrophotometer, along with the considerable evidence that a single aromatic hydrocarbon-inducible cytochrome P-450 isozyme is responsible for the catalysis, enhances the utility of this substrate in microsomal monooxygenase assays. The utility of the visible assay is further demonstrated by the simple determinations of the coupling ratio for 7-ethoxyresorufin oxidation in scup liver microsomes and the K1 for 7,8-benzoflavone and phenylimidazole inhibition of the enzymatic reaction.

Animals↗
PubMed1984

A technique for flat embedding and en face sectioning of the mammalian retina for autoradiography.

A method of tissue preparation is described which allows analysis of large areas of the mammalian retina in relatively few 2-5 micrometers sections, and which permits [3H]autoradiography with good resolution and low background. In contrast to standard methods of paraffin embedding and radial sectioning, we have embedded flattened retinas in glycol methacrylate resin and cut sections parallel to the plane of the retinal layers, i.e. en face. As previously shown (Sidman, 1970; Carter-Dawson and LaVail, 1979a, b), methacrylate embedding results in excellent cellular preservation and allows relatively thin sectioning appropriate for [3H]autoradiography and demonstration of cytological detail. Sectioning en face reduces the number of tissue sections required to survey large areas of the retina, and allows reconstruction of the topography of each retinal layer from serial sections. Thus, studies of retinal topography using [3H]autoradiography can now be more easily compared to studies of retinal topography using the whole-mount technique (see Stone, 1981).

Animals↗
PubMed1984

Synthesis and assembly of the cytoskeleton of Naegleria gruberi flagellates.

When Naegleria gruberi flagellates were extracted with nonionic detergent and stained by the indirect immunofluorescence method with AA-4.3 (a monoclonal antibody against Naegleria beta-tubulin), flagella and a network of cytoskeletal microtubules (CSMT) were seen. When Naegleria amebae were examined in the same way, no cytoplasmic tubulin-containing structures were seen. Formation of the flagellate cytoskeleton was followed during the differentiation of amebae into flagellates by staining cells with AA-4.3. The first tubulin containing structures were a few cytoplasmic microtubules that formed at the time amebae rounded up into spherical cells. The formation of these microtubules was followed by the appearance of basal bodies and flagella and then by the formation of the CSMT. The CSMT formed before the cells assumed the flagellate shape. In flagellate shaped cells the CSMT radiate from the base of the flagella and follow a curving path the full length of the cell. Protein synthetic requirements for the formation of CSMT were examined by transferring cells to cycloheximide at various times after initiation. One-half the population completed the protein synthesis essential for formation of CSMT 61 min after initiation of the differentiation. This is 10 min after the time when protein synthesis for formation of flagella is completed and 10-15 min before the time when the protein synthesis necessary for formation of the flagellate shape is completed.

Amoeba↗
PubMed1983

An aryl hydrocarbon hydroxylating hepatic cytochrome P-450 from the marine fish Stenotomus chrysops.

Hepatic microsomal cytochrome P-450 from the untreated coastal marine fish scup, Stenotomus chrysops, was solubilized and resolved into five fractions by ion-exchange chromatography. The major fraction, cytochrome P-450E (Mr = 54,300), was further purified to a specific content of 11.7 nmol heme/mg protein and contained a chromophore absorbing at 447 nm in the CO-ligated, reduced difference spectrum. NH2-terminal sequence analysis of cytochrome P-450E by Edman degradation revealed no homology with any known cytochrome P-450 isozyme in the first nine residues. S. chrysops liver NADPH-cytochrome P-450 reductase, purified 225-fold (Mr = 82,600), had a specific activity of 45-60 U/mg with cytochrome c, contained both FAD and FMN, and was isolated as the one-electron reduced semiquinone. Purified cytochrome P-450E metabolized several substrates including 7-ethoxycoumarin, acetanilide, and benzo[a]pyrene when reconstituted with lipid and hepatic NADPH-cytochrome P-450 reductase from either S. chrysops or rat. The purified, reconstituted monooxygenase system was sensitive to inhibition by 100 microM 7,8-benzoflavone, and analysis of products in reconstitutions with purified rat epoxide hydrolase indicated a preference for oxidation on the benzo-ring of benzo[a]pyrene consistent with the primary features of benzo[a]pyrene metabolism in microsomes. Cytochrome P-450E is identical to the major microsomal aromatic hydrocarbon-inducible cytochrome P-450 by the criteria of molecular weight, optical properties, and catalytic profile. It is suggested that substantial quantities of this aromatic hydrocarbon-inducible isozyme exist in the hepatic microsomes of some untreated S. chrysops. The characterization of this aryl hydrocarbon hydroxylase extends our understanding of the metabolism patterns observed in hepatic microsomes isolated from untreated fish.

Amino Acid Sequence↗
PubMed1983

Regioselectivity and stereoselectivity of androgen hydroxylations catalyzed by cytochrome P-450 isozymes purified from phenobarbital-induced rat liver.

The regioselectivity and stereoselectivity of androgen hydroxylations catalyzed by five isozymes of cytochrome P-450 purified from phenobarbital-induced rat liver were studied in a reconstituted monooxygenase system using testosterone (T) and androst-4-ene-3,17-dione (delta 4-A) as substrates. P-450 PB-3, an isozyme exhibiting low catalytic activity with many xenobiotic substrates, catalyzed efficient (turnover = 15.7 to 18.5 min-1 P-450-1 at 25 microM substrate) and highly stereoselective B-ring hydroxylations of both steroid substrates, with the corresponding 7 alpha- and 6 alpha-hydroxy alcohols formed in ratios of approximately 20 to 30:1, respectively. P-450 PB-2c metabolized testosterone to a mixture of 16 alpha OH-T, 2 alpha OH-T, and delta 4-A (product ratio = 1.0/0.78/0.33; turnover = 10.2 min-1 P-450-1). PB-2c is present in significantly larger amounts in mature male rats as compared to immature males, and probably catalyzes the male-specific testosterone 16 alpha-hydroxylase activity known to be induced at puberty and subject to endocrine control. P-450 PB-4, the major phenobarbital-induced isozyme in rat liver, catalyzed efficient D-ring hydroxylations, yielding 16 beta OH- delta 4-A as the predominant product with delta 4-A as substrate (turnover = 12.0 min-1 P-450-1) and a mixture of 16 beta OH-T, 16 alpha OH-T, and delta 4-A (the latter compound presumably formed via 17 alpha hydroxylation) with testosterone as substrate (turnover = 5.2 min-1 P-450-1). P-450 isozymes PB-1 and PB-5 hydroxylated both steroids with essentially the same regioselectivity as PB-4 but at only 5 to 10% the catalytic rate. Cytochrome b5 stimulated most of these steroid hydroxylations up to 2-fold with no change in regio- or stereoselectivity. The identification of specific steroid metabolites as diagnostic of particular P-450 isozymes should be useful for the assessment of isozymic contributions to microsomal activities and, in addition, facilitate comparisons of P-450 isozymes isolated in different laboratories.

Androgens↗