Progressive fixation of morphological polarity in the developing retina

Fixation of morphological polarity may not be an all-or-none event. The optic fissure of the chick retina normally lies ventrally. When optic vesicles were rotated 180°, the fissures later appeared ventral provided the operations were performed prior to Hamburger-Hamilton stage 12. Operations beyond stage 12 resulted in dorsal fissures. The lengths of the fissures varied in a manner indicating a gradual rather than abrupt change from ventral to dorsal with progressive stages of operation.     

Isolation and characterization of Populus isoperoxidases involved in the last step of lignin formation

Peroxidases (EC 1.11.1.7) from Populus x euramericana were investigated during the dormant and growing seasons using histochemical and biochemical methods. The activities of syringaldazine oxidase and p-paraphenylenediamine-pyrocatechol oxidase in sections of branches were maximal during spring in both phloem and young xylem. Cytoplasmic and cell-wall peroxidase activities from different lignified tissues were estimated in vitro. Pronounced differences were noticed between fractions isolated during spring and winter. Gel electrophoresis showed the presence of an anionic fast-migrating isoperoxidase group with a high syringaldazine-oxidase activity. The isoenzymes of this group were different in winter and in spring. The properties of these isoperoxidases (kinetic constants, pH optimum, resistance to heat) were investigated after isolation by ion-exchange chromatography.Abbreviations PPD-PC p-phenylenediamine-pyrocatechol - syr-oxidase syringaldazine-oxidase     

Radiation survival of vascular smooth muscle cells as a function of age

Late damage to normal tissues is an important consideration in determining the dose of radiation which can be delivered to a given target volume in clinical radiation therapy. The response of large blood vessels to radiation injury is undoubtedly complex and is influenced by (1) the cellular composition of the vessel wall, (2) the slow turnover of vascular cells, and (3) vascular repair mechanisms. As a first order model for radiation effects in large vessels, we have studied the radiobiologic properties of cultured vascular smooth muscle cells. We have measured survival curves and repair of sublethal radiation damage in exponentially growing cultures of rat aortic smooth muscle cells as a function of animal age and site of origin (thoracic versus abdominal aorta). Radiation survival parameters (utilizing two different mathematical models for the survival curve) and repair of sublethal damage did not appear to vary significantly as a function of animal age (3-23 months) or site or origin.     

Strain differences in the immune response of mice to homologous sperm-specific lactate dehydrogenase (LDH-C4).

The sperm-specific isozyme of murine lactate dehydrogenase (LDH-C4) was injected into female mice of various strains. Two regulatory phenotypes characterize the resultant immunity to LDH-C4: one is manifested by high, intermediate or low levels of response, the other by the immediate or delayed maturation of peak titer. The response of several strains can be classified as high (SWR, SJL, BABL/c, C3H/He) and intermediate to low (A, CBA, DBA/2, DBA/1, C57BL/6) according to the level of antibody production and cell mediated immunity. BALB/c, SJL and SWR strains are immediate responders while DBA/2 and C3H/He mice are clearly delayed responders. Maturation and magnitude of response do not appear to be related. Both the antibody and cell mediated responses are T-dependent, but are not obviously associated with Ig allotype or H-2 regulation.     

Effect of neocarzinostatin-induced strand scission on the template activity of DNA for DNA polymerase I.

Neocarzinostatin (NCS), an antitumor protein antibiotic that causes strand scissions of DNA both in vitro and in vivo, is shown to lower the template activity of DNA for DNA polymerase Iin vitro. There is a correlation between the extent of strand scission and the degree of inhibition, maximal inhibition of the polymerase reaction being obtained under conditions promoting maximal strand scission. These effects can be related to the concentrations of NCS and of 2-mercaptoethanol and are maximized by pretreatment of the DNA with drug. Results from polymerase assays in which the amount of drug-treated DNA template was varied at a constant level of the enzyme suggest that the sites associated with NCS-induced breaks are nonfunctional in DNA synthesis but bind DNA polymerase I. The binding of the enzyme to the inactive sites is further confirmed using [203 Hg] polymerase. It is shown that the lowering of the template activity of DNA by NCS under conditions of strand scission is due to the generation of a large number of inactive sites that block, competitively, the binding of DNA polymerase to the active sites on the template. Furthermore, the inhibition of DNA synthesis, which depends on the extent of strand breakage and on the relative amounts of template and enzyme, can be reversed by increasing the levels of template or polymerase. The finding that DNA synthesis directed by poly [d(A-T)] is much more sensitive to NCS than that primed by poly [d(G-C)] suggests that the drug preferentially interacts at regions containing adenine and/or thymine residues.     

Inhibition of chloramphenicol binding to Escherichia coli 70S ribosomes by 2'(3')-O-aminoacyl-dinucleoside phosphates derived from the aminoacyl-tRNA acceptor terminus.

The effect of 2' and 3'-O-aminoacyl-dinucleoside phosphates cytidylyl(3'-5')-2'(3')-O-L-phenyl-alanyladenosine (I), cytidylyl(3'-5')-3'-deoxy-2'-O-L-phenylalanyladenosine (IIa), cytidylyl(3'-5')-2'-deoxy-3'-O-L-phenylalanyladenosine (IIIa), cytidylyl(3'-5')-3'-deoxy-2'-O-glycyladenosine (IIb), cytidylyl(3'-5')-2'-deoxy-3'-O-glycyladenosine (IIIb), cytidylyl(3'-5')-3'-deoxy-2'-O-L-leucyladenosine (IIc), cytidylyl(3'-5')-2'-deoxy-3'-O-L-leucyladenosine (IIIc), cytidylyl(3'-5')-3'-O-L-phenylalanyladenosine (IIId) as analogs of the 2'(3')-aminoacyl-tRNA termini, on chloramphenicol binding to 70S Excherichia coli ribosomes was investigated. The association constants (Kb) of the investigated compounds were determined by the equilibrium dialysis method. Based on the constancy of Kb over the range of inhibitor concentration, it was determined that the binding site of the 2' isomers IIa-IIc overlaps with the chloramphenicol site, whereas the variability of Kb for the 3' isomers IIIb, IIIc and especially IIIa seems to indicate that they do not achieve a complete fit. The consistently higher values of the Kb values for the 3' isomers IIIa-IIIc relative to that of the 2' isomers IIa-IIc also indicate a stabilization of the binding of the former due to a specific interaction between its amino acid portion and a ribosomal site.     

Activation and inactivation of neocarzinostatin-induced cleavage of DNA.

The possible role of free radicals in the mechanism of neocarzinostatin (NCS) action was studied. While mercaptene markedly stimulate the ability of NCS to degrade DNA, they also rapidly inactivate the antibiotic in a preincubation and at higher concentration inhibit the degradation reaction. The radiation protector S,2-aminoethylisothiuronium bromide-HBr is the most potent compound tested. Scavengers of diffusible OH radicals, O2- or H2O2 do not result in significant inhibition of the oxygen-dependent cleavage of DNA by NCS; in fact, alcohols and other organic solvents stimulate the reaction several-fold. By contrast, the potent peroxyl free radical scavenger, alpha-tocopherol, blocks the reaction 50% at 50 micron.     

Daily variation in circulating lymphocyte counts, T and B proportions and responsiveness to phytohemagglutinin.

Peripheral blood was obtained from six healthy individuals over five consecutive days under uniform conditions and the total lymphocyte counts, T and B proportions, and response to phythohemagglutinin (PHA) were determined. The daily variation in T lymphocytes as measured by the spontaneous sheep erythrocyte (SRBC) assay was much greater when total T concentrations rather than T percentages were compared. There was considerable daily variation in PHA responsiveness and in the percentages of cells bearing Fc and C3 receptors and surface immunoglobulin (SIg). Cryopreservation did not affect the proportions of T and B lymphocytes although it resulted in a significant enhancement of PHA responsiveness following the freeze-thaw procedure. The significance of these results is discussed.