Evidence of the Direct Involvement of the Substrate TCP Radical in Functional Switching from Oxyferrous O2 Carrier to Ferric Peroxidase in the Dual-Function Hemoglobin/Dehaloperoxidase from Amphitrite ornata

Biochemistry ◽  
2014 ◽  
Vol 53 (30) ◽  
pp. 4956-4969 ◽  
Author(s):  
Shengfang Sun ◽  
Masanori Sono ◽  
Jing Du ◽  
John H. Dawson
Keyword(s):  
Dual Function ◽  
Direct Involvement ◽  
Amphitrite Ornata ◽  
Functional Switching

Structures of K42N and K42Y sperm whale myoglobins point to an inhibitory role of distal water in peroxidase activity

2014 ◽  
Vol 70 (11) ◽  
pp. 2833-2839 ◽  
Author(s):  
Chunxue Wang ◽  
Leslie L. Lovelace ◽  
Shengfang Sun ◽  
John H. Dawson ◽  
Lukasz Lebioda
Keyword(s):  
Peroxidase Activity ◽  
Physiological Role ◽  
Sperm Whale ◽  
Reaction Rates ◽  
Heme Iron ◽  
Oxygen Storage ◽  
Dual Function ◽  
Amphitrite Ornata ◽  
Coordinated Water

Sperm whale myoglobin (Mb) functions as an oxygen-storage protein, but in the ferric state it possesses a weak peroxidase activity which enables it to carry out H2O2-dependent dehalogenation reactions. Hemoglobin/dehaloperoxidase fromAmphitrite ornata(DHP) is a dual-function protein represented by two isoproteins DHP A and DHP B; its peroxidase activity is at least ten times stronger than that of Mb and plays a physiological role. The `DHP A-like' K42Y Mb mutant (K42Y) and the `DHP B-like' K42N mutant (K42N) were engineered in sperm whale Mb to mimic the extended heme environments of DHP A and DHP B, respectively. The peroxidase reaction rates increased ∼3.5-fold and ∼5.5-fold in K42Y and K42NversusMb, respectively. The crystal structures of the K42Y and K42N mutants revealed that the substitutions at position 42 slightly elongate not only the distances between the distal His55 and the heme iron but also the hydrogen-bonding distances between His55 and the Fe-coordinated water. The enhanced peroxidase activity of K42Y and K42N thus might be attributed in part to the weaker binding of the axial water molecule that competes with hydrogen peroxide for the binding site at the heme in the ferric state. This is likely to be the mechanism by which the relationship `longer distal histidine to Fe distance – better peroxidase activity', which was previously proposed for heme proteins by Matsuiet al.(1999) (J. Biol. Chem.274, 2838–2844), works. Furthermore, positive cooperativity in K42N was observed when its dehaloperoxidase activity was measured as a function of the concentration of the substrate trichlorophenol. This serendipitously engineered cooperativity was rationalized by K42N dimerization through the formation of a dityrosine bond induced by excess H2O2.

THE BALANCE OF PROBABILITY: STATISTICS AND THE DIACHRONIC STUDY OF ANCIENT HEBREW

2017 ◽  
Vol 25 (2) ◽  
pp. 927-960
Author(s):  
Jarod Jacobs
Keyword(s):  
Dead Sea Scrolls ◽  
Dead Sea ◽  
Biblical Hebrew ◽  
Large Datasets ◽  
Dual Function ◽  
Statistical Tools ◽  
Masoretic Text ◽  
Linguistic Research ◽  
Recent Debate ◽  
Diachronic Study

In this article, I discuss three statistical tools that have proven pivotal in linguistic research, particularly those studies that seek to evaluate large datasets. These tools are the Gaussian Curve, significance tests, and hierarchical clustering. I present a brief description of these tools and their general uses. Then, I apply them to an analysis of the variations between the “biblical” DSS and our other witnesses, focusing upon variations involving particles. Finally, I engage the recent debate surrounding the diachronic study of Biblical Hebrew. This article serves a dual function. First, it presents statistical tools that are useful for many linguistic studies. Second, it develops an analysis of the he-locale, as it is used in the “biblical” Dead Sea Scrolls, Masoretic Text, and Samaritan Pentateuch. Through that analysis, this article highlights the value of inferential statistical tools as we attempt to better understand the Hebrew of our ancient witnesses.

Dual-Function, Light Switchable Cobalt Catalysis via Active Site Metamorphosis

2019 ◽  
Author(s):  
Enrico Bergamaschi ◽  
Frédéric Beltran ◽  
Christopher Teskey
Keyword(s):  
Visible Light ◽  
Active Site ◽  
Catalytic Site ◽  
Dual Function ◽  
Catalytic Systems ◽  
Hydride Complex ◽  
Dual Functional ◽  
Multiple Processes ◽  
Olefin Migration

<p></p><p></p><p>Switchable catalysis offers opportunities to control the rate or selectivity of a reaction <i>via</i> a stimulus such as pH or light. However, few examples of switchable catalytic systems that can facilitate multiple processes exist. Here we report a rare example of such dual-functional, switchable catalysis. Featuring an easily prepared, bench-stable cobalt(I) hydride complex in conjunction with pinacolborane, we can completely alter the reaction outcome between two widely employed transformations – olefin migration and hydroboration – with visible light as the sole trigger. This dichotomy arises from ligand photodissociation which leads to metamorphosis of the active catalytic site, resulting in divergent mechanistic pathways.</p><p></p><p></p>

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