Nitric oxide synthases (NOSs) catalyze the formation of nitric oxide from L-arginine. We purified the heme containing, tetrahydrobiopterin-free, oxygenase domain of rat neuronal nitric oxide synthase (nNOSox) overexpressed in Escherichia coli. We found catalase activity in nNOSox. This is significant because H2O2 may also be a product of nitric oxide synthases. We found H2O2 assisted product formation from N-hydroxy-L-arginine and even from L-arginine both in the presence and in absence of tetrahydrobiopterin. We propose how heme moiety of the oxygenase domain alone is sufficient to carry out both steps of the NOS catalysis. © 2000 Federation of European Biochemical Societies.

S ADHIKARI

S RAY

R GACHHUI

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Catalase activity of oxygenase domain of rat neuronal nitric oxide synthase. Evidence for product formation from L-arginine.

FEBS Letters

Calmodulin (CAM) binding activates neuronal nitric-oxide synthase (nNOS) catalytic functions and also upregulates electron transfer into its flavin and heme centers. Here, we utilized seven tight binding CaM-troponin C chimeras, which, variably activate nNOS NO synthesis to examine the relationship between CaM domain structure, activation of catalytic functions, and control of internal electron transfer at two points within nNOS. Chimeras that were singly substituted with troponin C domains 4, 3, 2, or 1 were increasingly unable to activate NO synthesis, but all caused some activation of cytochrome c reduction compared with CaM-free nNOS. The magnitude by which each chimera activated NO synthesis was approximately proportional to the rate of heme iron reduction supported by each chimera, which varied from 0% to ~8% compared with native CaM and remained coupled to NO synthesis in all cases. In contrast, chimera activation of cytochrome c reduction was not always associated with accelerated reduction of nNOS flavins, and certain chimeras activated cytochrome c reduction without triggering heme iron reduction. We conclude: 1) CaM effects on electron transfer at two points within nNOS can be functionally separated. 2) CaM controls NO synthesis by governing heme iron reduction, but enhances reductase activity by two mechanisms, only one of which is associated with an increased rate of flavin reduction.

Fulltext

Journal of Biological Chemistry

Neuronal nitric-oxide synthase interaction with calmodulin- troponin C chimeras

Spectrophotometric and spectrofluorimetric studies reveal that an interaction occurs between hemoglobin and hematoporphyrin, a photosensitizing drug used in photodynamic therapy. Two concentration ranges of hematoporphyrin, 0.4-0.9 μM and 1.8-3.6 μM, representing significantly monomeric and aggregated (dimeric) state, respectively, have been used in the binding studies. The binding affinity constant (K) decreases, while the possible number of binding sites (p) increases as the concentration range of the porphyrin is increased. The nature of interaction has been studied by fluorescence quenching titration method under different ionic strengths and temperature conditions. It appears to be predominantly electrostatic and enthalpy-driven in the lower range of porphyrin concentration. However, the interaction follows mostly hydrophobic and entropy-driven modality in the higher concentration range of the ligand. The porphyrin-hemoglobin interaction results in release of oxygen from the protein. The extent of oxygen release depends on the stoichiometric ratio of hematoporphyrin:hemoglobin.

Journal of Photochemistry and Photobiology B: Biology

Studies on the interaction of hematoporphyrin with hemoglobin

Methods in Enzymology Analytical Ultracentrifugation

Author Index

SpringerReference

Meselson-Radding Model Of Recombination (1975 Proc Natl Acad Sci USA 72:358)

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Sigma‐Aldrich Corp.

Catalase activity of oxygenase domain of rat neuronal nitric oxide synthase. Evidence for product formation from L-arginine

Journal	Data powered by TypesetFEBS Letters
Publisher	Data powered by TypesetELSEVIER SCIENCE BV
ISSN	0014-5793