title: Requirement for reduced, unliganded hemoprotein for the hemoglobin- and myoglobin-mediated biotransformation of glyceryl trinitrate.
abstract: The biotransformation of glyceryl trinitrate (GTN) by hemoglobin (Hb) and myoglobin (Mb) was assessed using solutions of various forms of the hemoproteins, viz., the oxy-, deoxy-, carbonmonoxy- and met-forms. After incubation with these, GTN loss was observed only with the deoxy-forms of Hb and Mb. The stoichiometry and products of [14C]GTN biotransformation by deoxy-Hb and deoxy-Mb were determined by measuring the formation of [14C]glyceryl dinitrate [14C]GDN), met-Hb (or met-Mb) and inorganic nitrite anion. Biotransformation of GTN involved the oxidation of 2 mol of heme iron (II) per mol of GTN biotransformed to GDN and inorganic nitrite anion. In addition to the formation of GDN, 1 to 2.5% of the radioactivity could not be extracted from the incubation samples. The ratio of 1,2-GDN/1,3-GDN formed during incubation of deoxy-Hb with GTN was 11:1, which indicated a high degree of regioselectivity for the denitration of the nitrate ester group in position 1 or position 3 of GTN. The metabolite ratio obtained for deoxy-Mb incubation with GTN (1,2-GDN/1,3-GDN,3:1) was less than that for deoxy-Hb, which indicated less regioselectivity for the deoxy-Mb-mediated denitration reaction. This could reflect differences in the topography of the heme pocket of the two hemoproteins and steric differences in the GTN-hemoprotein interaction.
mesh_terms: D001711:Biotransformation; D006207:Half-Life; D006454:Hemoglobins / Q000378:metabolism*; D008706:Methemoglobin / Q000378:metabolism; D008786:Metmyoglobin / Q000378:metabolism; D009211:Myoglobin / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D005996:Nitroglycerin / Q000031:analogs & derivatives / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D006454:Hemoglobins; D009211:Myoglobin; D009573:Nitrites; D008786:Metmyoglobin; C014509:dinitroglycerol; C100003:deoxyhemoglobin; D008706:Methemoglobin; D005996:Nitroglycerin