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Results for “competition for substrate”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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38 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Identification of the cAMP response element that controls transcriptional activation of the insulin-like growth factor-I gene by prostaglandin E2 in osteoblasts

Insulin-like growth factor-I (IGF-I), a multifunctional growth factor, plays a key role in skeletal growth and can enhance bone cell replication and differentiation. We previously showed that prostaglandin E2 (PGE2) and other agents that increase cAMP activated IGF-I gene transcription in primary rat osteoblast cultures through promoter 1 (P1), the major IGF-I promoter, and found that transcriptional induction was mediated by protein kinase A. We now have identified a short segment of P1 that is essential for full hormonal regulation and have characterized inducible DNA-protein interactions involving this site. Transient transfections of IGF-I P1 reporter genes into primary rat osteoblasts showed that the 328-base pair untranslated region of exon 1 was required for a full 5.3-fold response to PGE2; mutation in a previously footprinted site, HS3D (base pairs +193 to +215), reduced induction by 65%. PGE2 stimulated nuclear protein binding to HS3D. Binding, as determined by gel mobility shift assay, was not seen in nuclear extracts from untreated osteoblast cultures, was detected within 2 h of PGE2 treatment, and was maximal by 4 h. This DNA-protein interaction was not observed in cytoplasmic extracts from PGE2-treated cultures, indicating nuclear localization of the protein kinase A-activated factor(s). Activation of this factor was not blocked by cycloheximide (Chx), and Chx did not impair stimulation of IGF-I gene expression by PGE2. In contrast, binding to a consensus cAMP response element (CRE; 5'-TGACGTCA-3') from the rat somatostatin gene was not modulated by PGE2 or Chx. Competition gel mobility shift analysis using mutated DNA probes identified 5'-CGCAATCG-3' as the minimal sequence needed for inducible binding. All modified IGF-I P1 promoterreporter genes with mutations within this CRE sequence also showed a diminished functional response to PGE2. These results identify the CRE within the 5'-untranslated region of IGF-I exon 1 that is required for hormonal activation of IGF-I gene transcription by cAMP in osteoblasts.

NASA Discipline Musculoskeletal↗
NASA NTRS2001

Fitting Vibrational Energy Parameters to Falloff Experiments: CH3 + CH3 + He (0.6-2 Torr 200-298 K)

There are many reported experiments and theoretical calculations for the combination of methyl free radicals diluted in a non-reactive 'deactivator. At high pressure the ethane (C2H6) combination product is the sole product; with decreasing pressure the chemically activated C2H6 will decompose. The falloff in the observed rate coefficient is the result of the competition between collisional stabilization of the chemically activated CA and unimolecular decomposition. The dependence of the rate coefficient on pressure, temperature and collision properties is complex and can not be calculated from first principles. The understanding of this system is not only of fundamental importance but is relevant to the recent detection of methyl free radicals in the atmospheres of Saturn - and Neptune. The temperatures of these outer planet atmospheres are in the 140-200 K region with total pressures (predominately H2 and He) less than 0.2 Torr. Experimentally determined rate coefficients have been reported for this reaction at T = 296-906 K and T = 200-408 K mostly with argon as the deactivator. At T = 200 K only the high pressure rate coefficient has been determined. Complete falloff curves over a wide temperature range (200-1600 K) with a variety of weak collider models used to simulate argon as the deactivator have also been reported by Klippenstein and Harding (KH). More recently we have reported the experimental rate coefficients in the falloff region with helium as the deactivator at 200 and 298 K. In this paper we have used the calculated falloff curves reported by KH for argon to determine the average energy transferred per collision for helium in our recently reported experiments. Collision rates were converted using Lennard Jones parameters; the temperature dependence of this conversion factor is noted. The helium experiments were consistent with a down of approximately 100 cm (exp-1); the temperature dependence was slight. The magnitude of down and its temperature dependence will be compared to other systems with similar substrate complexity and reaction energetics.

Tardy, Dwight C.↗