CADMIUM INDUCED INHIBITION OF NITRATE UPTAKE IN ANACYSTIS NIDULANS: INTERACTION WITH OTHER DIVALENT CATIONS

Abstract

The effect of Cd²⁺ (4ppm) and a combination of Cd²⁺ with the non-inhibitory levels of metals like Ca²⁺ (150ppm), Zn²⁺ (2ppm), and Hg²⁺ (0.04ppm) on the uptake of nitrate by Anacystis nidulans IU 625 (ATCC 27144) was investigated. The NO₃^- uptake kinetics was studied by monitoring short-term uptake rates at different NO₃^- levels (1-20mM). The values for V_max (0.8μmol/μg protein/hr) and half saturation constant for uptake (K_m 3.03mM) were obtained employing the double reciprocal plot. A 4ppm level of Cd²⁺ inhibited 50% of the NO₃^- uptake rate (at saturating NO₃^- level) compared to Cd²⁺-less control. Cd²⁺ inhibition of NO₃^- uptake (K_m 5.88mM) was alleviated as a result of competitive interaction by either Ca²⁺ (K_m 4.34mM) or Zn²⁺ (K_m 4.08mM). Hg²⁺ ions, however, interacted synergistically with Cd²⁺ (K_m 12.5mM). There was no change in the uptake capacity (V_max 0.8μmol/μg protein/hr) for NO₃^- under various treatments.