Hemoglobin Cowtown
Over a thousand different human hemoglobin variants are known.Many have altered function. Hemoglobin variants have historicallybeen names for the city in which they were identified. One exampleis hemoglobin Cowtown (Ft. Worth, Texas). Here is an abridgedversion of the original case report for this particular variant(Schneider et al. (1979) Am J Clin Pathol 72:1028-1032). The A4post quiz is based on this report.
A 20 year old white male travelled from Fort Worth to DenverColorado, on vacation. Shortly after disembarking from theaircraft, he experienced a sever throbbing headache, which was notrelieved by analgesics, and which became so unbearable that he andhis family decided to return home the following day. To thepatient's surprise, after several hours in the pressurizedairliner, the headache subsided. Upon his return to Fort Worth, hisfamily physician admitted him to the hospital forinvestigation.
The results of the physical examination were not remarkable, butthe hematologic findings indicated erthrocytosis (increased redblood cells). Other laboratory data showing the following:
Arterial blood pH 7.39 pCO2 102 torr pO2 37 torr Total blood volume elevated Packed erythrocyte volume elevated
Electrophoresis (proteins moving through a gel according totheir net charge in the presence of an electric current) at pH 8.5showed normal pattern for hemoglobin, but analysis at pH 6 revealeda hemoglobin chain with abnormal mobility. Further testingdetermined a single His -> Leu substitution in shift for HbCowtown relative to normal Hb A. The Bohr effect (a measure of theinfluence of pH on oxygen affinity) was only half the normalvalue
QUESTION 2: Urea denatured hemoglobin alpha and beta chainsmigrate as bands in an electrophoretic system according to theirnet charge at a defined pH. The beta chain of Hb Cowtown has asingle His -> Leu substitution. Given a mixture of normal andCowtown Beta chains, order the chains according to their increasingmobility toward the anode (+) relative to each other.
electrophoresis buffer normal Beta chain Cowtown Beta chain pH 8.9 lower mobility, equal mobility, or higher mobility lower mobility, equal mobility, or higher mobility pH 6 lower mobility, equal mobility or higher mobility lower mobility, equal mobility or higher mobility
Hemoglobin Cowtown
Over a thousand different human hemoglobin variants are known.Many have altered function. Hemoglobin variants have historicallybeen names for the city in which they were identified. One exampleis hemoglobin Cowtown (Ft. Worth, Texas). Here is an abridgedversion of the original case report for this particular variant(Schneider et al. (1979) Am J Clin Pathol 72:1028-1032). The A4post quiz is based on this report.
A 20 year old white male travelled from Fort Worth to DenverColorado, on vacation. Shortly after disembarking from theaircraft, he experienced a sever throbbing headache, which was notrelieved by analgesics, and which became so unbearable that he andhis family decided to return home the following day. To thepatient's surprise, after several hours in the pressurizedairliner, the headache subsided. Upon his return to Fort Worth, hisfamily physician admitted him to the hospital forinvestigation.
The results of the physical examination were not remarkable, butthe hematologic findings indicated erthrocytosis (increased redblood cells). Other laboratory data showing the following:
| Arterial blood pH | 7.39 |
| pCO2 | 102 torr |
| pO2 | 37 torr |
| Total blood volume | elevated |
| Packed erythrocyte volume | elevated |
Electrophoresis (proteins moving through a gel according totheir net charge in the presence of an electric current) at pH 8.5showed normal pattern for hemoglobin, but analysis at pH 6 revealeda hemoglobin chain with abnormal mobility. Further testingdetermined a single His -> Leu substitution in shift for HbCowtown relative to normal Hb A. The Bohr effect (a measure of theinfluence of pH on oxygen affinity) was only half the normalvalue
QUESTION 2: Urea denatured hemoglobin alpha and beta chainsmigrate as bands in an electrophoretic system according to theirnet charge at a defined pH. The beta chain of Hb Cowtown has asingle His -> Leu substitution. Given a mixture of normal andCowtown Beta chains, order the chains according to their increasingmobility toward the anode (+) relative to each other.
| electrophoresis buffer | normal Beta chain | Cowtown Beta chain |
| pH 8.9 | lower mobility, equal mobility, or higher mobility | lower mobility, equal mobility, or higher mobility |
| pH 6 | lower mobility, equal mobility or higher mobility | lower mobility, equal mobility or higher mobility |
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Hemoglobin Cowtown
Over a thousand different human hemoglobin variants are known.Many have altered function. Hemoglobin variants have historicallybeen names for the city in which they were identified. One exampleis hemoglobin Cowtown (Ft. Worth, Texas). Here is an abridgedversion of the original case report for this particular variant(Schneider et al. (1979) Am J Clin Pathol 72:1028-1032). The A4post quiz is based on this report.
A 20 year old white male travelled from Fort Worth to DenverColorado, on vacation. Shortly after disembarking from theaircraft, he experienced a sever throbbing headache, which was notrelieved by analgesics, and which became so unbearable that he andhis family decided to return home the following day. To thepatient's surprise, after several hours in the pressurizedairliner, the headache subsided. Upon his return to Fort Worth, hisfamily physician admitted him to the hospital forinvestigation.
The results of the physical examination were not remarkable, butthe hematologic findings indicated erthrocytosis (increased redblood cells). Other laboratory data showing the following:
| Arterial blood pH | 7.39 |
| pCO2 | 102 torr |
| pO2 | 37 torr |
| Total blood volume | elevated |
| Packed erythrocyte volume | elevated |
Electrophoresis (proteins moving through a gel according totheir net charge in the presence of an electric current) at pH 8.5showed normal pattern for hemoglobin, but analysis at pH 6 revealeda hemoglobin chain with abnormal mobility. Further testingdetermined a single His -> Leu substitution in shift for HbCowtown relative to normal Hb A. The Bohr effect (a measure of theinfluence of pH on oxygen affinity) was only half the normalvalue
QUESTION 3: The mutation in Hb Cowtown results in severeimpairment of the Bohr effect, yet does not alter the equilibriumbetween the R and T states. This is surprising since thecarboxyl-terminal residue His B146 is clearly invalid instabilization of the T state. Deduce the allosteric roles of eachionizable group in the C terminal residue.
| His B146 alpha carboxyl | Answer choices: None, T state stabilization, R statestabilization, Bohr effect |
| His B146 imidazole | Answer choices: None, T state stabilization, R statestabilization or Bohr effect |
| His B146 alpha amine | Answer choices: None, T state stabilization, R statestabilization or Bohr effect |
