Hydration-dependent conformational states of hemoglobin. Equilibrium and kinetic behavior.
The equilibrium and kinetics of methemoglobin conversion to hemichrome induced by dehydration were investigated by visible absorption spectroscopy. Below about 0.20 g water per g hemoglobin only hemichrome was present in the sample; above this value, an increasing proportion of methemoglobin appeared with the increase in hydration. The transition between the two derivatives showed a time-dependent biphasic behavior and was observed to be reversible. The rates obtained for the transition of methemoglobin to hemichrome were 0.31 and 1.93 min-1 and for hemichrome to methemoglobin 0.05 and 0.47 min-1. We suggest that hemichrome is a reversible conformational state of hemoglobin and that the two rates observed for the transition between the two derivatives reflect the alpha- and beta-chains of hemoglobin.
Instituto de Biociências, Letras e Ciências Exatas, UNESP, S. José do Rio Preto, Brazil.
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Colombo
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Sanches
D003890:Desiccation; D006420:Hemeproteins / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008706:Methemoglobin / Q000737:chemistry*; D011487:Protein Conformation / Q000187:drug effects; D013053:Spectrophotometry; D014867:Water / Q000494:pharmacology*
D006420:Hemeproteins; C001332:hemichrome; D014867:Water; D008706:Methemoglobin