Time-resolved CARS measurements of vibrational decoherence of I₂ isolated in matrix Ar

Time-resolved coherent anti-Stokes Raman scattering is applied to prepare and interrogate vibrational coherences on the ground electronic surface of molecular iodine isolated in Ar matrices. The coherence decay time shows a linear dependence on vibrational quantum numbers, for v = 3–15. The temperature dependence of decoherence rates is negligible for v < 7, in the experimental range T = 18–32 K. For a v = 13, 14 superposition, the temperature dependence indicates dephasing by a 66 cm–¹ pseudo-local phonon, just outside the Debye edge of the solid. The accuracy of the data is limited due to two-photon induced dissociation of the molecule, which process is characterized using polarized fields. The T → 0 limit of dephasing is discussed

Time-resolved CARS measurements of the vibrational decoherence of I2 isolated in an Ar matrix

Time-resolved coherent anti-Stokes Raman scattering is applied to prepare and interrogate vibrational coherences on the ground electronic surface of molecular iodine isolated in Ar matrices. The coherence decay time shows a linear dependence on vibrational quantum numbers for v=3-15. The temperature dependence of decoherence rates is negligible for v&lt;7 in the experimental range T=18-32 K. For a v=13, 14 superposition, the temperature dependence indicates dephasing by a 66 cm(-1) pseudo-local phonon, just outside the Debye edge of the solid. The accuracy of the data is limited due to two-photon induced dissociation of the molecule, a process which is characterized using polarized fields. The T--&gt;0 limit of dephasing is discussed. (C) 2003 American Institute of Physics

Introduction of a new respiratory mechanism into human hemoglobin

Previous studies on bovine hemoglobin (HbBv) have suggested amino acid substitutions, which might introduce into human hemoglobin (HbA) functional characteristics of HbBv, namely a low intrinsic oxygen affinity regulated by Cl(-). Accordingly, we have constructed and characterized a multiple mutant, PB5, [beta(V1M + H2 Delta + T4I + P5A + A76K)] replacing four amino acid residues of HbA with those present at structurally analogous positions in HbBv, plus an additional substitution, beta T4I, which does not occur in either HbBv or HbA. This 'pseudobovine' hemoglobin has oxygen binding properties very similar to those of HbBv: the P(50) of HbA, PB5 and HbBv in the absence of Cl(-) are 1.6, 4.6 and 4.8 torr, respectively, and in 100 mM Cl(-) are 3.7, 10.5 and 12 torr, respectively. Moreover, PB5 has 3-fold slower autoxidation rate compared to HbA and HbBv. These are desirable characteristics for a human hemoglobin to be considered for use as a clinical artificial oxygen carrier. Although the functional properties of PB5 and HbBv are similar, van't Hoff plots indicate that the two hemoglobins interact differently with water, suggesting that factors regulating the R to T equilibrium are not the same in the two proteins. A further indication that PB5 is not a functional mimic of HbBv derives from PB5(control), a human hemoglobin with the same substitutions as PB5, except the beta T4I replacement. PB5(control) has a high oxygen affinity (P(50)=2.3 torr) in the absence of Cl(-), but retains the Cl(-) effect of PB5. The Cl(-) regulation of oxygen affinity in PB5 involves lysine residues at beta 8 and beta 76. PB4, which has the same substitutions as PB5 except beta A76K, and PB6, which has all the substitutions of PB5 plus beta K8Q, both have a low intrinsic oxygen affinity, like HbBv and PB5, but exhibit a decreased sensitivity to Cl(-). Since HbBv has lysine residues at both beta 8 and beta 76, these results imply that Cl(-) regulation in HbBv likewise involves these two residues. The mechanism responsible for the low intrinsic oxygen affinity of HbBv remains unclear. It is suggested that residues peculiar to HbBv at the alpha(1)beta(1) interface may play a role

Allosteric modulation by tertiary structure in mammalian hemoglobins. Introduction of the functional characteristics of bovine hemoglobin into human hemoglobin by five amino acid substitutions.

Bovine erythrocytes do not contain 2,3-diphosphoglycerate, the principal allosteric effector of human hemoglobin. Bovine hemoglobin has a lower oxygen affinity than human hemoglobin and is regulated by physiological concentrations of chloride (Fronticelli, C., Bucci, E., and Razynska, A. (1988) J. Mol. Biol. 202, 343-348). It has been proposed that the chloride regulation in bovine hemoglobin is introduced by particular amino acid residues located in the amino-terminal region of the A helix and in the E helix of the beta subunits (Fronticelli, C. (1990) Biophys. Chem. 37, 141-146). In accordance with this proposal we have constructed two mutant human hemoglobins, beta(V1M+H2deleted+T4I+P5A) and beta(V1M+H2deleted+T4I+P5A+A76K). These are the residues present at the proposed locations in bovine hemoglobin except for isoleucine at position 4. Oxygen binding studies demonstrate that these mutations have introduced into human hemoglobin the low oxygen affinity and chloride sensitivity of bovine hemoglobin and reveal the presence of a previously unrecognized allosteric mechanism of oxygen affinity regulation where all the interactions responsible for the lowered affinity and chloride binding appear to be confined to individual beta subunits

Regulation of COX2 expression in mouse mammary tumor cells controls bone metastasis and PGE2-induction of regulatory T cell migration.

BACKGROUND: The targeting of the immune system through immunotherapies to prevent tumor tolerance and immune suppression are at the front lines of breast cancer treatment and research. Human and laboratory studies have attributed breast cancer progression and metastasis to secondary organs such as the bone, to a number of factors, including elevated levels of prostaglandin E2 (PGE2) and the enzyme responsible for its production, cyclooxygenase 2 (COX2). Due to the strong connection of COX2 with immune function, we focused on understanding how variance in COX2 expression manipulates the immune profile in a syngeneic, and immune-competent, mouse model of breast cancer. Though there have been correlative findings linking elevated levels of COX2 and Tregs in other cancer models, we sought to elucidate the mechanisms by which these immuno-suppressive cells are recruited to breast tumor and the means by which they promote tumor tolerance. METHODOLOGY/PRINCIPAL FINDINGS: To elucidate the mechanisms by which exacerbated COX2 expression potentiates metastasis we genetically manipulated non-metastatic mammary tumor cells (TM40D) to over-express COX2 (TM40D-COX2). Over-expression of COX2 in this mouse breast cancer model resulted in an increase in bone metastasis (an observation that was ablated following suppression of COX2 expression) in addition to an exacerbated Treg recruitment in the primary tumor. Interestingly, other immune-suppressive leukocytes, such as myeloid derived suppressor cells, were not altered in the primary tumor or the circulation. Elevated levels of PGE2 by tumor cells can directly recruit CD4+CD25+ cells through interactions with their EP2 and/or EP4 receptors, an effect that was blocked using anti-PGE2 antibody. Furthermore, increased Treg recruitment to the primary tumor contributed to the greater levels of apoptotic CD8+ T cells in the TM40D-COX2 tumors. CONCLUSION/SIGNIFICANCE: Due to the systemic effects of COX2 inhibitors, we propose targeting specific EP receptors as therapeutic interventions to breast cancer progression