Characterization of hemoglobin bassett (alpha94Asp-->Ala), a variant with very low oxygen affinity.
Hemoglobin (Hb) Bassett, an abnormal Hb variant with a markedly reduced oxygen affinity, was discovered in a Caucasian (Anglo-Saxon) male child who experienced episodes of cyanosis. Cation-exchange and reversed-phase (RP) high-performance liquid chromatography (HPLC) showed that the patient has an abnormal Hb, with a mutation in the alpha-globin. Tryptic peptide digest of the abnormal alpha-globin with subsequent HPLC analysis revealed abnormal elution of the alpha-T11 peptide. Further studies with Edman sequencing and electrospray mass spectrometry of tryptic peptide alpha-T11, as well as structural analysis by X-ray crystallography revealed an Asp-->Ala substitution at the alpha94 (G1) position, a match for Hb Bassett. Detailed functional studies showed that this Hb variant had a markedly reduced oxygen affinity (P(50) at pH 7.0 = 22 mmHg; Hb A P(50) = 10.5 mmHg), reduced Bohr effect (-0.26 compared to - 0.54 in Hb A), and low subunit cooperativity (n = 1.4, compared to 2.6 in Hb A). X-ray crystallography results explain the probable effects of the structural modification on the oxygen-binding properties of this Hb variant.
Abdulmalik
Osheiza
O
Division of Hematology, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104, USA.
Safo
Martin K
MK
Lerner
Norma B
NB
Ochotorena
Josiree
J
Daikhin
Evgueni
E
Lakka
Vinaysagar
V
Santacroce
Rosa
R
Abraham
Donald J
DJ
Asakura
Toshio
T
D000409:Alanine / Q000235:genetics; D019943:Amino Acid Substitution; D001224:Aspartic Acid / Q000235:genetics; D002648:Child; D002852:Chromatography, Ion Exchange / Q000379:methods; D018360:Crystallography, X-Ray; D006441:Hemoglobin A / Q000378:metabolism; D006455:Hemoglobins, Abnormal / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008958:Models, Molecular; D009154:Mutation; D010100:Oxygen / Q000097:blood* / Q000737:chemistry; D010108:Oxyhemoglobins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010313:Partial Pressure; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism
D006455:Hemoglobins, Abnormal; D010108:Oxyhemoglobins; D021122:Protein Subunits; D001224:Aspartic Acid; D006441:Hemoglobin A; D000409:Alanine; D010100:Oxygen