Kinetics of carboxymyoglobin and oxymyoglobin studied by picosecond spectroscopy.
Picosecond studies of carboxymyoglobin (MbCO) and oxymyoglobin (MbO2) reveal that excitation at 530 nm induces photodissociation at less than 8 ps. The kinetic and structural changes were monitored by following absorbance changes at selected wave-lengths in the Soret (B) band and in the Q band. Within the 10 ps-0.45 ns period of time over which our experiments were conducted, the absorbance changes in the Soret and Q bands for MbCO and MbO2 correspond to the conventional long-term, steady-state deoxymyoglobin difference spectra (Mb-MbCO and Mb-MbO2), as determined by comparison of isosbestic, maximum, and minimum points. In addition, MbCO exhibits a decay to a steady state in the Soret band (monitored at 440 nm). The onset of the decay immediately follows photodissociation and has a rate of (8 +/- 3) X 10(9) s-1 (tau = 125 +/- 50 ps). During the 10 ps-0.45 ns observation window, relaxation is not seen for MbO2 in the Soret band, nor is relaxation observed in the Q band for either MbCO or MbO2. We conclude from these results that the steady state that we observed for MbCO and MbO2 is most likely the stable form of deoxymyoglobin, and the relaxational differences between MbCO and MbO2 observed in the Soret band indicate that the electronic destabilization after ligand detachment is very different for these molecules. We believe that these relaxational differences may be related to differences in tertiary structural changes, or due to the fact that the MbCO (S = 0) molecule passes through an intermediate spin Mb (S = 1) state before relaxing the the Mb (S = 2) state.
D000818:Animals; D002248:Carbon Monoxide / Q000378:metabolism; D007501:Iron; D007700:Kinetics; D009211:Myoglobin / Q000378:metabolism*; D011485:Protein Binding; D013053:Spectrophotometry; D013997:Time Factors; D014907:Whales
D009211:Myoglobin; C018013:carboxymyoglobin; C017595:oxymyoglobin; D002248:Carbon Monoxide; D007501:Iron
Proc Natl Acad Sci U S A. 1936 Apr;22(4):210-6
16577697
J Mol Biol. 1965 May;12:88-118
14343300
Nature. 1964 Apr 4;202:83-4
14166723
Nature. 1957 Dec 21;180(4599):1416-7
13493540
Proc Natl Acad Sci U S A. 1977 Jul;74(7):2612-3
268611
Proc Natl Acad Sci U S A. 1977 Apr;74(4):1315-9
266173
Proc Natl Acad Sci U S A. 1978 Feb;75(2):573-7
273220
Nature. 1970 Nov 21;228(5273):726-39
5528785
Nature. 1974 Jan 4;247(5435):62-4
4808946
Ann N Y Acad Sci. 1973;206:210-22
4356180
Annu Rev Biochem. 1975;44:209-32
237460
Proc Natl Acad Sci U S A. 1974 Feb;71(2):558-62
4521822
Proc Natl Acad Sci U S A. 1975 Jun;72(6):2335-9
1056005
Science. 1976 Jul 2;193(4247):50-1
935853
Anal Biochem. 1975 May 12;65(1-2):445-8
1130690
J Chem Phys. 1970 Aug 1;53(3):963-7
5432674
J Chem Phys. 1967 Nov 15;47(10):4166-72
6065104
Biochemistry. 1967 Apr;6(4):1216-22
6032466
J Mol Biol. 1966 Jul;18(3):385-404
5966294
Biochemistry. 1966 Jan;5(1):365-85
5938952