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Studies of Hemoglobin Denaturation and Heinz Body Formation in the Unstable Hemoglobins

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Studies of Hemoglobin Denaturation and Heinz Body Formation in the Unstable Hemoglobins Studies of Hemoglobin Denaturation and Heinz Body Formation in the Unstable Hemoglobins Christine C. Winterbourn, R. W. Carrell J Clin Invest. 1974;54(3):678-689. https://doi.org/10.1172/JCI107806. Research Article The sequential changes that occur during the precipitation on mild heating of the unstable hemoglobins, Hb Christchurch, Hb Sydney, Hb Köln, and Hb A, were examined with particular attention to the possibility of an accompanying oxidative process. Hb Christchurch, Hb Sydney, and Hb A precipitated with equal amounts of α- and β-chains and full heme complement. Hb Köln, however, was one-half hemedepleted and showed a slight excess of precipitated β-chains. In all cases the spectrum of the precipitated material was typical of a hemichrome. There was no evidence that sulfhydryl oxidation contributed to the precipitation process. Reduced glutathione was unable to protect the hemoglobin against precipitation, and mixed disulfide formation between the precipitating hemoglobin and glutathione was insignificant, even in the presence of excess glutathione. No blockade of β93 cysteines could be demonstrated in the unstable hemoglobins. Precipitation of oxyhemoglobin and carboxyhemoglobin in all cases gave nonspecific oxidation of approximately two of the six hemoglobin sulfhydryl groups to give intra- and intermolecular disulfide bonds. Single α- and β-chains, plus polymers of up to five or six chains linked by disulfide bridges, were demonstrated by polyacrylamide gel electrophoresis. This disulfide oxidation was not observed with deoxy- or methemoglobin and did not appear to influence the rate of precipitation. These findings fit the theoretical prediction that autoxidation of oxy- and carboxyhemoglobin is […] Find the latest version: https://jci.me/107806/pdf Studies of Hemoglobin Denaturation and Heinz Body Formation in the Unstable Hemoglobills CHRISTINE C. WINTERBOURN and R. W. CARRELL From the Department of Clinical Biochemistry, Christchurch Hospital, Christchurch, New Zealand A B S T R A C T The sequential changes that occur dur- that the usual precipitating event is altered bonding at ing the precipitation on mild heating of the unstable the heme to give the formation of hemichromes. There is hemoglobins, Hb Christchurch, Hb Sydney, Hb K6ln, no evidence of an accompanying oxidative process that and Hb A, were examined with particular attention to could pose a threat to the integrity of the red cell. the possibility of an accompanying oxidative process. Hb Christchurch, Hb Sydney, and Hb A precipitated with equal amounts of a- and A-chains and full heme INTRODUCTION complement. Hb K6ln, however, was one-half heme- The intracellular precipitation of hemoglobin to form depleted and showed a slight excess of precipitated Heinz bodies occurs in hemolytic anemias associated 13-chains. In all cases the spectrum of the precipitated with the unstable hemoglobins. The defect in these un- material was typical of a hemichrome. There was no stable hemoglobins usually involves important internal evidence that sulfhydryl oxidation contributed to the bonding amino acids, particularly those forming bonds precipitation process. Reduced glutathione was unable to with the heme group. The reason for the instability of protect the hemoglobin against precipitation, and mixed the hemoglobin is therefore quite well understood at disulfide formation between the precipitating hemoglobin the molecular level, but there is still a lack of knowledge and glutathione was insignificant, even in the presence of the changes occurring during precipitation and the of excess glutathione. No blockade of 193 cysteines could ultimate cause of hemolysis (1-3). be demonstrated in the unstable hemoglobins. The similarity to events observed in the oxidative Precipitation of oxyhemoglobin and carboxyhemo- hemolytic anemias has led to proposals that the precipi- globin in all cases gave nonspecific oxidation of ap- tation of the unstable hemoglobins is accompanied by proximately two of the six hemoglobin sulfhydryl groups oxidative changes. The oxidative hemolytic anemias to give intra- and intermolecular disulfide bonds. Single arise either from formation of excess oxidizing products a- and 1-chains, plus polymers of up to five or six chains (as with acetylphenylhydrazine administration) or from linked by disulfide bridges, were demonstrated by poly- breakdown of protective mechanisms against oxidants acrylamide gel electrophoresis. This disulfide oxidation (as in glucose-6-phosphate dehydrogenase deficiency). was not observed with deoxy- or methemoglobin and In either case, the end result is the same as with the un- did not appear to influence the rate of precipitation. stable hemoglobins; the precipitation of hemoglobin, These findings fit the theoretical prediction that autoxi- the formation of Heinz bodies, and hemolysis. In the dation of oxy- and carboxyhemoglobin is accompanied case of the oxidative hemolytic anemias, the presence by formation of a free radical, with the reactions of of free oxidants as well as precipitated hemoglobin this free radical being confined intramolecularly. could pose a direct threat to the cell membrane. Together, these results are in keeping with predictions Two proposals have been made that could explain based on the known structural abnormalities of the un- similar oxidative effects in the unstable hemoglobin stable hemoglobins, all of which result in greater mo- hemolytic anemias. Jacob (4) has put forward a gen- lecular flexibility. Our findings support the conclusion eral mechanism of Heinz body formation based on sulf- Received for publication 25 May 1973 and in revised form hydryl oxidation that has received support in other re- 14 January 1974. views (5, 6). He proposed that there is initial loss of 678 The Journal of Clinical Investigation Volume 54 September 1974-678-689 the heme groups from the affected chains, with oxidation The hemoglobin solution was passed through Sephadex G25 of specific (P93) sulfhydryl groups to give mixed di- before reaction to remove glutathione reductase substrates, and afterwards to remove excess sulfides with followed GSSG. Hb K6ln was glutathione, by precipitation of purified by column chromatography on DEAE Sephadex the abnormal chains to give Heinz bodies. He also by the method of Huisman and Dozy (9). proposed that a major contribution to the accompanying Heat precipitates of hemoglobin and various derivatives hemolysis is disturbance of the cell membrane by mixed were prepared by incubating 2%o hemolysates in pH 7.4 disulfide bond formation between membrane proteins phosphate buffer at 50'C (precipitation of unstable hemo- or 60'C and the Alternatively. globins) (precipitation of Hb A). Precipitates precipitated hemoglobin. Carrell were separated by centrifugation, washed twice with water, (7) has proposed that the defects in the unstable henio- and dissolved in 3% sodium dodecyl sulfate (SDS) immedi- globins could allow water to gain access to the oxy- ately before analysis. When removal of an early-precipi- genated heme iron, resulting in the formation of methe- tating nonhemoglobin protein was desired, hemolysates were moglobin and highly reactive superoxide ions. The end preincubated at 60°C for 15-30 min, and the initial pre- cipitate was discarded. At intervals during the precipitation result could be the release of superoxide with effects of unstable hemoglobins, supernates were examined for the analogous to those seen with acetylphenylhydrazine. In presence of a-chains by starch gel electrophoresis at pH the present study, we have looked for evidence of oxi- 8.6 (Tris-citrate/borate system) followed by staining with dative processes accompanying hemoglobin precipitation, o-tolidine (10). and also examined in detail the sequence of events pro- Protein was estimated by the Lowry modification of the by Folin-Ciocalteu method (11). Sulfhydryl groups were mea- posed Jacob. sured with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) as The molecular defects that cause unstable hemoglobins described by Ellman (12). Available sulfhydryl groups in to precipitate intracellularly to form Heinz bodies also hemoglobin were determined in pH 8.0 phosphate buffer, cause their accelerated precipitation on mild heating, and total sulfhydryl groups in the same buffer containing and in the two to be 1% SDS. Reduced glutathione (GSH) was estimated by many ways processes appear similar. the DTNB method described by Prins and Loos (13). Heme Detailed information on the changes that accompany heat groups were determined by adding the solution of native precipitation should therefore contribute to the under- or precipitated hemoglobin to a known excess of cold standing of the mechanism of Heinz body formation. acetone containing 1% HCI, centrifuging to separate the We have studied the heat precipitation of three unstable precipitated globin, and determining the absorbance of the acetone solution at 538 nm. The method was calibrated hemoglobins: Hb Christchurch' Phe -- Hb (P71 Ser), against standard hemoglobin solutions. Spectra of acid ace- Sydney (,867 Val-> Ala), and Hb K6ln (P98 Val -> tone solutions obtained from native and precipitated hemo- Met) and also Hb A, which behaves like the unstable globin were identical. Hemoglobin was determined as cyan- hemoglobins when subjected to proportionately greater methemoglobin. heat stress. We have determined the heme content and To examine precipitated hemoglobin for the presence of bound subunit of the extent covalently cysteine or glutathione, globin
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