Open AccessStudies on Substrate Specificity of S‐Adenosylmethionine: Protein‐Carboxyl Methyltransferase from Calf Brain
Author(s) -
OLIVA Adriana,
GALLETTI Patrizia,
ZAPPIA Vincenzo,
PAIK Woon Ki,
KIM Sangduk
Publication year - 1980
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1980.tb04463.x
Subject(s) - chemistry , sulfonium , stereochemistry , steric effects , methyl group , amino acid , side chain , butyric acid , methylation , substrate (aquarium) , methyltransferase , enzyme , methionine , biochemistry , organic chemistry , alkyl , dna , biology , ecology , salt (chemistry) , polymer
Kinetic properties of protein methylase II (S‐adenosylmethionine:protein‐carboxyl methyltrans‐ ferase, EC 2.1.1.24), which methylates the free carboxyl groups of protein substrates, were studied with various analogs and derivatives of S ‐adenosyl‐ l ‐methionine (AdoMet) and S ‐adenosyl‐ l ‐ homocysteine (AdoHcy), using corticotropin as methyl‐accepting polypeptide. Experiments with methyl‐labelled structural analogs of AdoMet showed that the replacement of the amino groups of AdoMet by hydroxyl groups, as well as the removal of the carboxyl group, results in a loss of methylating ability of the molecule. Deaminated and decarboxylated derivatives were also inactive as inhibitors. Among the sulfonium analogs tested, only S ‐adenosyl‐ l ‐ (2‐amino‐4‐carboxymethylthio)butyric acid exerted a significant inhibition. AdoHcy, the demethylated product of AdoMet, exerts a competitive inhibition on the reaction (K i = 0.65 μM); the probable regulatory role of this inhibition will be discussed. The removal of the adenine amino group of the thioether resulted in a loss of the inhibitory effect. Experiments with the D‐isomer of AdoHcy showed the relevance of the steric configuration of the α‐carbon in the binding to the enzyme protein. 5′‐Methylthioadenosine, a metabolic product of AdoMet, in‐ hibited competitively the reaction ( K i = 41 μM) while 5′‐methylthioadenosine derivatives, such as n ‐butylthioadenosine, isobutylthioadenosine and thioethanoladenosine, failed to exert any in‐ hibition. Three synthetic polypeptides differing in amino acid composition and in chain length have also been tested as methyl‐acceptor substrates and as inhibitors for the reaction. Only the copolymer of l ‐glutamic acid and l ‐tyrosine [poly(Glul 1.16 , Tyrl)] (M r = 22600) exerts a relevant non‐com‐ petitive inhibition, while none of the tested synthetic polypeptides is active as substrate.