The role of the medium in long-range electron transfer

 The role of the polypeptide matrix in electron transfer processes in proteins has been studied in two distinct systems: first in a protein where the induced ET is artificial, and second as part of the catalytic cycle of an enzyme. Azurins are structurally well-characterized blue single-copper proteins consisting of a rigid β-sheet polypeptide matrix. We have determined rate constants and activation parameters for intramolecular long-range electron transfer between the disulfide radical anions (generated by pulse radiolysis) and the copper(II) centre as a function of driving force and nature of the intervening medium in a large number of wild-type and single-site-mutated proteins. In ascorbate oxidase, for which the three-dimensional structure is equally well characterized, the internal ET from the type-I Cu(I) to the trinuclear Cu(II) centre has been studied. We find that the results correlate well with distance through well-defined pathways using a through-bond electron tunnelling mechanism. Received: 2 January 1997 / Accepted: 6 February 1997     

Characterization by cytofluorometry of the different types of adenohypophyseal cells in the rat

The different antehypophysical cell types which synthetize and release somatotroph (GH), corticothroph (ACTH), gonadotroph (LH-FSH) and lactotroph (PRL) hormones were analysed. The experiments were performed on hypophyses from five groups of animals: adult males, 14 days-old female, adult females, gestating adult females and lactating adult females. The cells were analysed by immunofluorescence using flow cytometry. For each of the hormones studied, there was a characteristic spectral distribution of cells. The evolution of cell size and granular content with respect to sex and physiological state of each group was studied by the analysis of diffused light. Small, slightly granular cells represented 50% of the cell population in males and 14 day-old females but only 8% in gestating or lactating females. The study of the cell cycle showed the presence of dividing cells in the population of large, granular cells from gestating and from lactating females. No features of cell division were observed in the population of small, slightly granular cells. This study indicates the potential value of multiparametric analysis in the separation of pure sub-populations of antehypophysial cells.     

Expression of class I histocompatibility antigens in neuroectodermal tumors is independent of the expression of a transfected neuroblastoma myc gene

We have evaluated the relationship between the neuronal myc gene (NMYC) and class I major histocompatibility complex (MHC) expression in human neuroblastoma (NB) tumor cell lines. Class I MHC surface Ag expression in NB cell lines varied from nearly undetectable to levels nearly as high as in a lymphoblastoid cell line. Class I MHC mRNA levels in NMYC-amplified NB cell lines were lower than levels observed in single copy NMYC NB cell lines. However, considerable variation in class I MHC surface Ag and mRNA expression was evident in NMYC-amplified cell lines. To determine directly whether NMYC might modulate class I MHC expression in NB, we transfected a plasmid containing a recombinant NMYC gene into two tumor cell lines derived from a NB and a related neuroepithelioma tumor. Constitutive overexpression of the recombinant NMYC gene produced no consistent change in class I MHC surface Ag or mRNA levels. To determine whether class I MHC expression might be developmentally regulated in adrenal medullary cells, the precursor cells of adrenal NB tumors, beta 2-microglobulin expression was measured in fetal and adult adrenal glands. beta 2-Microglobulin expression was not evident in the neuroblasts of a 24-wk-old fetal adrenal gland, whereas beta 2-microglobulin expression was present in the adult adrenal medulla. These data suggest that variation in class I MHC expression among NB cells may reflect the developmental stage at which neuroblasts were arrested during tumorigenesis.     

Plasminogen activator is an apparent lymphocyte mitogen

Culture fluids of avian sarcoma virus (ASV)-transformed but not normal chicken embryo cells frequently elicited a mitogenic response in normal avian and murine lymphocytes. We examined the possibility that plasminogen activator (PA) might be responsible for the observed mitogenic effect. PA activity, present in culture medium, was correlated positively with lymphocyte mitogenic capacity. Treatment of cells with phorbol myristate acetate, which elevates PA levels, increased mitogenesis. Similar treatment with dexamethasone, which inhibits PA biosynthesis and/or secretion, reduced lymphocyte mitogenic activity. Addition to culture fluids of either benzamidine or diisopropylfluorophosphate, both specific PA inhibitors, blocked lymphocyte proliferative responsiveness to culture fluids. In contrast, neither epsilon-amino-caproic acid nor trasylol, which inhibits plasmin esterase activity but not PA, abrogated lymphocyte responsiveness. Furthermore, purified urokinase, an enzyme of similar substrate specificity to PA, had lymphocyte stimulatory activity. These results strongly suggest that PA can function as a lymphocyte mitogen.     

The effects of prolonged deep freezing on the biomechanical properties of osteochondral allografts

Musculo-skeletal allografts sterilized and deep frozen are among the most common human tissue to be preserved and utilized in modern medicine. The effects of a long deep freezing period on cortical bone has already been evaluated and found to be insignificant. However, there are no reports about the influences of a protracted deep freezing period on osteochondral allografts. One hundred osteochondral cylinders were taken from a fresh specimen and humeral heads of 1 year, 2 years, 3 years and 4 year old bones. Twenty chips from each period, with a minimum of 3 chips per humeral head. Each was mechanically tested by 3 point compression. The fresh osteochondral allografts were significantly mechanically better than the deep frozen osteochondral allografts. There was no statistical significant time dependent difference between the deep frozen groups in relation to the freezing period. Therefore, we conclude that, from the mechanical point of view deep freezing of osteochondral allografts over a period of 4 years, is safe without further deterioration of the biomechanical properties of the osteochondral allografts.