title: Atypical profiles and modulations of heme-enzymes catalyzed outcomes by low amounts of diverse additives suggest diffusible radicals' obligatory involvement in such redox reactions.
abstract: BACKGROUND
  Peroxidations mediated by heme-enzymes have been traditionally studied under a single-site (heme distal pocket), non-sequential (ping-pong), two-substrates binding scheme of Michaelis-Menten paradigm. We had reported unusual modulations of peroxidase and P450 reaction outcomes and explained it invoking diffusible reactive species [Manoj, 2006; Manoj et al., 2010; Andrew et al., 2011, Parashar et al., 2014 & Venkatachalam et al., 2016].
  
  
  METHODS
  A systematic investigation of specific product formation rates was undertaken to probe the hypothesis that involvement of diffusible reactive species could explain undefined substrate specificities and maverick modulations (sponsored by additives) of heme-enzymes.
  
  
  RESULTS
  When the rate of specific product formation was studied as a function of reactants' concentration or environmental conditions, we noted marked deviations from normal profiles. We report that heme-enzyme mediated peroxidations of various substrates are inhibited (or activated) by sub-equivalent concentrations of diverse redox-active additives and this is owing to multiple redox equilibriums in the milieu. At low enzyme and peroxide concentrations, the enzyme is seen to recycle via a one-electron (oxidase) cycle, which does not require the substrate to access the heme centre. Schemes are provided that explain the complex mechanistic cycle, kinetics & stoichiometry.
  
  
  CONCLUSIONS
  It is not obligatory for an inhibitor or substrate to interact with the heme centre for influencing overall catalysis. Roles of diffusible reactive species explain catalytic outcomes at low enzyme and reactant concentrations.
  
  
  CONCLUSIONS
  The current work highlights the scope/importance of redox enzyme reactions that could occur "out of the active site" in biological or in situ systems.
authors.affiliation: Satyamjayatu: The Science & Ethics Foundation, Kulappully, Shoranur-2, Kerala 679122, India; Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India; REDOx Lab, PSG Institute of Advanced Studies, Coimbatore, Tamil Nadu 641004, India; School of Chemical and Bio Technology, SASTRA University, Thanjavur, Tamil Nadu 613401, India; Late Lowell P. Hager's Lab, Department of Biochemistry, University of Illinois (U-C), 600, S Mathews Avenue, Urbana, IL 61801, USA. Electronic address: satyamjayatu@yahoo.com.
authors.forename: Kelath Murali
authors.initials: KM
authors.lastname: Manoj
authors.affiliation: Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India.
authors.forename: Abhinav
authors.initials: A
authors.lastname: Parashar
authors.affiliation: REDOx Lab, PSG Institute of Advanced Studies, Coimbatore, Tamil Nadu 641004, India.
authors.forename: Avanthika
authors.initials: A
authors.lastname: Venkatachalam
authors.affiliation: Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India.
authors.forename: Sahil
authors.initials: S
authors.lastname: Goyal
authors.affiliation: Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India.
authors.lastname: Satyalipsu
authors.affiliation: School of Chemical and Bio Technology, SASTRA University, Thanjavur, Tamil Nadu 613401, India.
authors.forename: Preeti Gunjan
authors.initials: PG
authors.lastname: Singh
authors.affiliation: Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India.
authors.forename: Sudeep K
authors.initials: SK
authors.lastname: Gade
authors.affiliation: Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India.
authors.forename: Kalaiselvi
authors.initials: K
authors.lastname: Periyasami
authors.affiliation: Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India; Department of Biosciences & Bioengineering, IIT-Bombay, Powai, Mumbai, Maharashtra 400076, India.
authors.forename: Reeba Susan
authors.initials: RS
authors.lastname: Jacob
authors.affiliation: Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India.
authors.forename: Debosmita
authors.initials: D
authors.lastname: Sardar
authors.affiliation: Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India.
authors.forename: Shanikant
authors.initials: S
authors.lastname: Singh
authors.affiliation: Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India.
authors.forename: Rajan
authors.initials: R
authors.lastname: Kumar
authors.affiliation: CIDR-MCBL, Indian Institute of Science, Bengaluru, Karnataka 560012, India; Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu 632014, India. Electronic address: dnlndrwster@gmail.com.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Gideon
mesh_terms: D001203:Ascomycota / Q000201:enzymology*; D002384:Catalysis; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D005656:Fungal Proteins / Q000737:chemistry*; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000737:chemistry*
chemical_list: D005656:Fungal Proteins; D003577:Cytochrome P-450 Enzyme System; D009195:Peroxidase
keywords: Heme-enzymes; Modulation; P450; Peroxidase; Redox reaction