Haemoglobin Tak: a β‐Chain Elongation

Abstract

S ummary . In Haemoglobin Tak two normal α‐chains are combined with two β‐chains elongated by 11 residues beyond the C‐terminus. Unlike in the α‐chain abnormal Hb Constant Spring, the elongation cannot result from a point mutation of a stop codon. It is probably due to an unequal crossing‐over near the 3′ end of the β‐chain structural gene. This could cause either a deletion of the normal stop codon or a shift in the reading frame. Oxygen dissociation of purified Hb Tak shows no cooperativity but in Hb A + Tak haemolysates there is no interaction between the two above 40% O 2 saturation. Heterozygotes for Hbs A and Tak show an imbalance of globin chain synthesis (α/non α= 1.5), the synthesis of β Tak resembles that of the β‐chain in β + thalassaemia.