ISSN:
1432-1017
Keywords:
Hemerythrin
;
Oxygenation
;
Lingula unguis
;
Stopped-flow
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Physics
Notes:
Abstract O2-jump experiments with an improved stopped-flow apparatus have been used to study oxygenation and deoxygenation processes in Lingula unguis hemerythrin. With an O2 electrode set in the observation cell, O2 concentration conld be obtained directly. The reliability of this method has been compared with other conventional methods. O2-jump (up and down) experiments were carried out with L. unguis hemerythrin at pH 6.8 (non-cooperative pH) and at pH 7.6 (cooperative pH). At pH 6.8, both O2-jump (up) and O2-jump (down) experiments showed single exponential processes which were consistent with the following scheme: $${\text{Hr + O}}_{\text{2}} \mathop \rightleftharpoons \limits_{{\text{k}}_{{\text{off}}} }^{{\text{k}}_{{\text{on}}} } {\text{HrO}}_{\text{2}} $$ . The value of k on was estimated to be (4.4 ± 0.5) × 105 M−1 s −1, and k off was (15 ± 5) s−1. These values are consistent with those obtained by the temperature-jump method (Zimmer et al. 1986). At pH 7.6, O2-jump (up) experiments showed two relaxation processes, whereas O2-jump (down) experiments showed a single exponential process. The faster process in the O2-jump (up) experiments could be attributed to the same process as that seen in the temperature-jump experiments (Zimmer et al. 1986). The slower process in the O2-jump (up) experiments corresponds to the process obtained in the O2-jump (down) experiments. The results are discussed in terms of a state with intermediate affinity in O2-binding and with the possible existence of a slow step in O2-binding.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00185415
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