Influence of carboxyl groups on conformation of histone H1 from Ceratitis capitata.

Salt and pH-dependent effects on the local conformation of the two tyrosine residues of the histone H1 from the fruit fly Ceratitis capitata have been studied by difference spectroscopy, circular dichroism (CD), fluorescence emission and quenching of tyrosine emission by KI. Four different solvent conditions were used: pH 1.0 and pH 6.0 in the presence or absence of 1 M NaCl. The results clearly indicate a partial folding of the fruit fly histone H1 in the absence of NaCl upon pH increasing from 1.0 to 6.0. This folding is achieved only through ionization of acidic side chains which leads to an environment of the tyrosine residues similar to that found in salt-folded histone H1. Furthermore, the present results give new insights into the states of the tyrosine residue responsible for the tyrosinate-like fluorescence emission at 340 nm described previously (Jordano, J., Barbero, J.L., Montero, F. & Franco, L. (1983) J. Biol Chem. 258, 315-320).