title: Picosecond photodissociation and subsequent recombination processes in carbon monoxide hemoglobin.
abstract: Excitation of HbCO by a single 6-psec 530-nm pulse results in photodissociation with a first-order constant of 0.89 X 10(11) sec-1. The kinetics of photodissociation, monitored by following absorbance changes in the Soret band at 440 nm, are interpreted as corresponding to predissociation followed by a corssing into a dissociative state. Subsequent recombination of CO with the porphyrin system and protein structural transformations were monitored by use of a continuous He-Cd laser beam spatially coincident with the photolysis and Soret interrogation beams at the sample. We find that the latter events take place in three distinct time regions, depending on exciation pulse energy and repetition rate. Exictation of HbCO with a single pulse (0.8--5 mJ) results in a relaxation to the ground state with an associative first-order constant of 5 X 10(3) sec-1. With a 100-pulse train (approximately 7.5 mJ), a new decay grows with a rate constant of 63 sec-1. For a pulse-train energy of 12 mJ or higher, a delay occurs at the onset of the second (slower) recombination.
mesh_terms: D002248:Carbon Monoxide; D006454:Hemoglobins; D007700:Kinetics; D011485:Protein Binding; D011487:Protein Conformation; D013057:Spectrum Analysis
chemical_list: D006454:Hemoglobins; D002248:Carbon Monoxide
references.citation: J Mol Biol. 1965 May;12:88-118
references.pmid: 14343300
references.citation: Biochem J. 1959 Feb;71(2):293-303
references.pmid: 13628568
references.citation: J Physiol. 1956 Oct 29;134(1):123-34
references.pmid: 13377315
references.citation: Eur J Biochem. 1975 Apr 1;52(3):589-93
references.pmid: 19242
references.citation: J Biol Chem. 1967 Oct 25;242(20):4678-81
references.pmid: 6061413
references.citation: Nature. 1970 Nov 21;228(5273):726-39
references.pmid: 5528785
references.citation: Science. 1975 Mar 7;187(4179):836-8
references.pmid: 1114327
references.citation: J Biol Chem. 1976 Mar 25;251(6):1533-42
references.pmid: 3499
references.citation: Prog Biophys Mol Biol. 1975;29(3):225-320
references.pmid: 738
references.citation: Proc Natl Acad Sci U S A. 1974 Feb;71(2):558-62
references.pmid: 4521822
references.citation: Biochemistry. 1974 Jul 16;13(15):3111-7
references.pmid: 4841058
references.citation: Biochem Biophys Res Commun. 1972 Apr 14;47(1):187-93
references.pmid: 5063633
references.citation: J Biol Chem. 1972 Jan 10;247(1):319-21
references.pmid: 5019948
references.citation: Eur J Biochem. 1972 Feb;25(3):491-7
references.pmid: 5043317
references.citation: Science. 1976 Jul 2;193(4247):50-1
references.pmid: 935853
references.citation: Biochemistry. 1975 Dec 2;14(24):5355-73
references.pmid: 1191643
references.citation: J Biol Chem. 1975 Jan 25;250(2):790-2
references.pmid: 1112790
references.citation: Anal Biochem. 1975 May 12;65(1-2):445-8
references.pmid: 1130690
references.citation: J Biol Chem. 1969 Sep 10;244(17):4664-7
references.pmid: 5808509
references.citation: J Mol Biol. 1967 Aug 28;28(1):117-56
references.pmid: 6051747