| Popis: |
The effect of different divalent and monovalent cations on reactions catalyzed by the Escherichia coli tRNA nucleotidyltransferase has been examined. The highest rates of incorporation of AMP into tRNA—pX—C—C or tRNA—pX and of CMP into tRNA—pX are observed in the presence of Mg2+. Mn2+ is less efficient than Mg2+ for AMP incorporation; it is inefficient for CMP incorporation; in its presence UMP is incorporated instead of CMP. Co2+ shows only low efficiency in all cases examined. In the presence of optimal Mg2+ concentration, Mn2+ decreases the rate of incorporation of CMP and, to a lower extent, of AMP, but increases the rate of UMP incorporation. K+ at 0.1 M concentration stimulates CMP incorporation in both tRNA—pX and tRNA—pX—C whereas it has an inhibitory effect on AMP and UMP incorporation in all cases. The role of thiol groups on enzyme activity has been examined using —SH blocking reagents. 5,5′-Dithiobis(2-nitrobenzoic) acid or N-ethylmaleimide inhibit the incorporation of AMP into tRNA—pX—C—C but are without effect on the incorporation of CMP or UMP into tRNA—pX. |
