D. Yee et Fmm. Morel, IN-VIVO SUBSTITUTION OF ZINC BY COBALT IN CARBONIC-ANHYDRASE OF A MARINE DIATOM, Limnology and oceanography, 41(3), 1996, pp. 573-577
We examined the mechanism by which Co additions partially alleviate th
e growth limitation of marine diatoms in cultures with low Zn concentr
ations. Cultures of the coastal diatom Thalassiosira weissflogii were
grown under low-Zn conditions and provided with low and high levels of
Co. Enzyme assays and autoradiographs of electrophoresis gels of cell
ular proteins revealed that a large fraction of the Co is found in the
main isoform of the enzyme carbonic anhydrase (CA), where most of the
Zn is located. The affinity of CA for Co is lower than for Zn, and th
e Go-substituted enzyme is less active than the native Zn form. Compar
isons of growth under different partial pressures of CO2 show that Co
can ameliorate the growth of carbon-limited cultures. We conclude that
Co alleviates Zn limitation via direct substitution in CA, which is i
mportant for carbon acquisition.