Response of the Bohr group salt bridges to ligation of the T state of haemoglobin Kansas.

New types of polyheads of bacteriophage lambda, produced by two defective mutants (def K13 and def K213; Katsura, 1976) in the major head protein, were studied by electron microscopy and optical diffraction, and compared with the normal polyheads consisting of non-mutated major head protein molecules. The new polyheads were found to be interesting for the following three reasons.

1.

(1) They provide a good experimental system in which to study the changes in the quaternary structure due to small perturbations in the primary structure of protein molecules. The results of measurements of their pitch angle and width agreed with the rule of “constant near-equatorial lattice line curvature” proposed by Steven et al. (1976). This rule can be explained theoretically if one assumes that hypothetical ring-like nuclei are formed during the assembly of polyheads.

2.

(2) Some of the polyheads produced by one of the mutants (def K213) have irregularities such as capping, widening, bending and branching. These irregularities seem to be due to the presence of a small number of pentamer(s) and/or heptamers(s) in the lattice consisting of hexamers. Theoretical predictions based on this assumption agree with the results.

3.

(3) A one-sided image of the lambda head shell was obtained by optical filtering of the def K213 polyheads which have pitch angles that are different from 30 °. The filtered image revealed the arrangements of structural units in the capsomers.