Crystal structure of constitutive endothelial nitric oxide synthase: a paradigm for pterin function involving a novel metal center

Article Abstract:

A high-resolution crystal structure of a constitutive endothelial nitric oxide synthase (eNOS) heme domain, alone and in combination with tetrahydrobiopterin (H4B), is presented. A catalytic role for H4B is evidenced by the similarity of the pterin-binding site in NOS with other pterin-using enzymes. Structural evidence for the ability of the substrate, L-arginine, to bind at the site of H4B is also presented. Based on the substrate's cofactory mimicry, a mechanism that involves the involvement of a pterin radical cation in the catalytic cycle leading to nitric oxide biosynthesis is identified.

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Constitutive expression of the CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) gene disrupts circadian rhythms and suppresses its own expression

Article Abstract:

Plants sense and respond to light by means of photoreceptors and circadian clocks. In the Arabidopsis, the CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) gene have been isolated. This gene encodes a transcription factor necessary for phytochrome responsiveness. Efforts to further investigate its role in circadian regulation revealed that the CCA1 possess several characteristics expected of the central oscillator. Its constitutive expression was found to affect a number of circadian-regulated processes. In addition, a feedback repression mechanism was observed for its circadian oscillation.

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Constitutive activation of Src family kinases in mouse embryos that lack Csk

Article Abstract:

C-Src kinase (csk), a cytoplasmic protein-tyrosine kinase, inhibits the kinase activity of Src family members by phosphorylating the negative regulatory tyrosine residue of Src. Csk-deficient embryos of mice exhibit characteristic abnormality in the development of neural tissues when the expression of p60 (super c-src) increases. An elevation in the kinase activity of p60 (super c-src) in csk-deficient embryos is due to a substantial reduction of phosphate on Tyr-527. Csk acts as anti-oncogene through its negative regulation of Src family kinases.

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