No abstract

Bovine tryptophanyl-tRNA synthetase (TrpRS, E.C. 6.1.1.2) is unable to catalyze in vitro formation of Ap4A in contrast to some other aminoacyltRNA synthetases. However, in the presence of L-tryptophan, ATP-Mg 2÷ and ADP the enzyme catalyzes the Ap3A synthesis via adenylate intermediate. Ap3A (not Ap4A) may serve as a substrate for TrpRS in the reaction of E. (Trp ~ AMP) formation and in the tRNA Tw charging. The Km value for Ap3A was higher than the Km for ATP (approx. 1.00 vs. 0.22 mM) and Vm~x was 3 times lower than for ATP. The Zn2+-deficient enzyme catalyzes Ap3A synthesis in the absence of exogenous ADP due to ATPase activity of Zn2+-deprived TrpRS. The inability of mammalian TrpRS to synthesize Ap4A, might be considered as a molecular tool preventing the removal of Zn 2÷ due to chelation by Ap4A and therefore preserving the enzyme activity.

No abstract

Homogeneous preparations of bovine tryptophanyl‐tRNA synthetase (EC 6.1.1.2) contain monosaccharides (mannose, fucose, galactose, N‐acetylglucosamine) as revealed by liquid chromatography. Their content comprises 2.5–3.0% (w/w) of the enzyme composed of two subunits (60 kDa × 2). The same set of sugars was detected in clastase and CNBr‐generated fragments (with molecular masses of approx. 40 kDa and 30 kDa, respectively). It is concluded that bovine tryptophanyl‐tRNA synthetase, in addition to being a metallo‐ and phosphoprotein, is also a glycoprotein.

Activity in ~he presenc~ of L-v~ne methy] ease, a~fl of L-3-arn~no-4-me~hylp~n1~.~-2-one (rne~yLk,et.~ne) WaS ~ea~ured in the ~am~ way. inhibitionThe ra~,e of ~rever~ib]e kr--~,a'b~-~fon was f~owed by assaying ~e~tty ,(as in 2~.) :an s~anp]e~ at diff~ren~ time~ zfie:r mixing enzyme and ~ ~uh~:bitcr. The ~bitor~, ch]or,orneihyLketones, L-valhae mad L-aspaztme aua]ogUes were incubated w~t~ enzyme ira 0.05 ~M K-phosphate . buffer, pH 7.5 at 25~C. The kine dc constants of 5,~bAbi-don were de;retained v,5 ~th a ] O.0-foid concenlradon ex~.ess of ]nh~bitox o~er e~az3cme. purified beef liver valyl-tRNA syn~et,'~e was oblzSn 2Ao Test for pos~ble reae~q~arion by he p~:o~edure ha ~7] with naoditSca~tioJ~s t,o be " Enzyme (3 n~g/an])was 5a~:mabmed for 5 h~-Lu ~lhe descr~bed ,~lsewhe~.-The preparation eontained ~raeez prose-~c,e o~ 5 X-a:0 -4 aM ~h]0r0rnOllaytke~one or:..~ethyi ofsome other synthetasez anfl.!some olheI pxo~e.ins, .ketone a~ in 2,3, A]iquots were :ddluled 100-fold and