Tyrosine-containing proteins histones

The fluorescence of purified histones has been studied by several different groups, 90 95) with the most detailed studies being on calf thymus histone HI. Histone HI, which binds to the outside of core particles, contains one tyrosine and no tryptophan. This protein exhibits a substantial increase in fluorescence intensity in going from a denatured to a folded state.<90) Collisional quenching studies indicate that the tyrosine of the folded HI is in a buried environ-ment.(91) Libertini and Small(94) have identified three emissions from this residue when in the unfolded state with peaks near 300, 340, and 400 nm. The 340-nm peak was ascribed to tyrosinate (vide infra), and several possibilities were considered for the 400-nm component, including room temperature phosphorescence, emission of a charge transfer complex, or dityrosine. Dityrosine has the appropriate spectral characteristics, but would require... 

The 50% inhibition concentration of erbstatin against tyrosine kinase was 0.55 p,g/ml, when it was examined as follows The reaction mixture contained 1 mM MnCl2, 100 ng EGF, 40 lg protein of A431 membrane fraction, 75 lg of albumin, 3 lg of histone, and HEPES (N-2-hydroxyethylpiperazine-N -2-ethanesulfonic acid) buffer (20 mM, pH 7.4) in a final volume of 50 (11. The reaction tubes were placed on ice and incubated for 10 minutes in the presence or absence of erbstatin. The reaction was initiated by the addition of labeled ATP (10 (11), and the incubation was continued for 30 minutes at 0°C. Then aliquots of 50 (11 were pipetted onto Whatman 3MM filter paper and put immediately into a beaker of cold 10% TCA containing 0.01 M sodium pyrophosphate. The filter papers were washed extensively with TCA solution containing 0.01 M sodium pyrophosphate at room temperature, extracted with ethanol and ether, and then dried. Radioactivity was measured by a scintillation counter. 

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