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METHYLATION OF E. COLI TRANSFER RIBONUCLEIC ACIDS BY A tRNA ADENINE‐l‐METHYLTRANSFERASE FROM RAT BRAIN CORTEX AND BULK‐ISOLATED NEURONS
Author(s) -
Salas Carlos E.,
Sellinger Otto Z.
Publication year - 1978
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1978.tb12436.x
Subject(s) - transfer rna , biochemistry , enzyme , biology , spermidine , ribosomal rna , methyltransferase , substrate (aquarium) , methylation , microbiology and biotechnology , rna , dna , ecology , gene
— Brain cortices or bulk‐isolated neuronal cell bodies prepared from cortices of 8‐day old male rats were used as the source of a l‐methyl adenine‐specific tRNA methyltransferase (tRNA‐AMT). Ammonium sulfate fractionation and chromatography on spheroidal hydroxylapatite and Sephadex G‐200 yielded an 80‐fold purified enzyme, as determined by using E. coli bulk tRNA as substrate. The kinetic parameters of tRNA‐AMT for the substrate S ‐adenosyl‐ l ‐methionine (SAM) ( K m = 6 μM) and the inhibitor, S ‐adenosyl‐ l ‐homocysteine (SAH) ( K i = 3.4 μ m ) were determined and several SAH analogs tested as inhibitors. S ‐Adenosyl‐ l ‐cysteine (SAC) ( 10 ‐4 m ) and S ‐adenosyl‐ d ‐homocysteine (SADH) (10 ‐4 m ) produced a 35 and a 21% reduction in enzyme activity, respectively. The effects of Mg 2+ , NH 4 + acetate and of the polyamines spermine, putrescine and spermidine on the brain tRNA‐AMT mimicked the effects of these agents on hepatic tRNA‐AMT (G lick et al , 1975). Comparing the ability of cerebral tRNA‐AMT to methylate E. coli tRNA glu2 , tRNA val , tRNA phe and bulk tRNA revealed tRNA glu2 as the best and tRNA phe as the least effective substrate. tRNA‐AMT prepared from neuronal cell bodies showed closely similar characteristics to the cortical enzyme. A comparison of the activities of tRNA‐AMT in neurons and glial cells revealed higher values in the former.