POLYMETALLIC HYDROLYTIC ZINC ENZYMES - PROBING THE SITE OF NUCLEASE P1 THROUGH COBALT(II) SUBSTITUTION

Partial Co(II) substitution in the three-zinc site of P. citrinum nucl ease P1 has been achieved. The Co(II) ion is found to bind to the site of the most EDTA-labile Zn atom with an 80% site occupancy. An affini ty constant of 10(5) M(-1) for metal binding was determined from the v isible spectra which also indicate a six-coordinate Co(II) geometry. T he hyperfine-shifted H-1 NMR resonances suggest that metal substitutio n occurred at the Zn3 site (X-ray atom numbering).