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Measurement of isoelectric point of S‐adenosyl‐L‐methionine and its metabolic products by an isoelectric focusing technique
Author(s) -
Farooqui Jamal,
Kim Sangduk,
Paik Woon K.
Publication year - 1983
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.1150040402
Subject(s) - sulfonium , methionine , isoelectric point , chemistry , isoelectric focusing , homocysteine , energy charge , stereochemistry , biochemistry , chromatography , organic chemistry , amino acid , adenylate kinase , enzyme , salt (chemistry)
The isoelectric point (p I ) of S‐adenosyl‐L‐methionine and some of its metabolic products has been determined by an isoelectric focusing technique. The experimental p I values of S‐adenosyl‐L‐methionine and S‐methylmethionine are 7.24 and 6.85, respectively, and the p I values of S‐adenosyl‐L‐homocysteine and homocysteine are 6.05 and 5.65, respectively. This indicates that the contribution by adenosine, adenine and ribose to the total electric charge of S‐adenosyl‐L‐methionine or S‐adenosyl‐L‐homocysteine is approximately 0.40 p I unit. The differences in the p I values between two pairs of compounds (S‐adenosyl‐L‐methionine vs. S‐adenosyl‐L‐homocysteine and S‐methylmethionine vs. methionine) are very close (1.19 and 1.14, respectively). This difference is the amount of p I value contributed by the sulfonium group which has been formed by methyl addition. Surprisingly, the presence of a permanent positive charge at the sulfonium center in S‐adenosyl‐L‐methionine and S‐methylmethionine does not result in a higher p I values for these compounds. This might be due to the partial neutralization of the positive charge by the formation of carbanion. The mechanism of charge neutralization in these sulfonium compounds is discussed.