Chemical and Enzymatic Modification of Membrane Proteins and Anion Transport in Human Red Blood Cells
The paper is introduced by a review of the developments which lead to the suggestion of an involvement of the protein in band 3 (nomenclature of Steck, ref.2) in anion transport across the red cell membrane. Subsequently, it is shown that DIDS and its dihydroderivative H2DIDS, which both played an essential role in the reviewed work, not only combine with the protein in band 3 but also with other membrane constituents. At maximal inhibition 1.1–1.3 molecules of DIDS or H2DIDS are bound per molecule of protein in band 3. Combined treatment with 3h pDIDS and esternai chymotrypsin, pronase or papain demonstrates the existence of peptides in the protein in band 3 which differ with respect to their accessibility or susceptibility to proteolysis. Each enzyme affects the protein differently and produces different changes of anion transport. In contrast to external trypsin which has neither an effect on the protein in band 3 nor on anion transport, internal trypsin splits the protein in band 3 completely. Fragments of 58,000 and 48,000 Daltons remain attached to the membrane while other products of hydrolysis are released into the medium. Anion transport is partially inhibited but continues to exhibit the essential features seen in the intact cell. The described results are compatible with an involvement of some component of the protein in band 3 in anion transport. They show that additional evidence is required to provide more definitive proof of such involvement.
KeywordsMembrane Protein Anion Transport Enzymatic Modification Disulfonic Acid Membrane Constituent
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