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Kinetics of Carboxylmethylation of the Charge Isoforms of Myelin Basic Protein by Protein Methyltransferase II
Author(s) -
Caamaño Claudio A.,
Azcurra Julio M.,
Sellinger Otto Z.,
Zand Robert
Publication year - 1989
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.1471-4159.1989.tb09257.x
Subject(s) - gene isoform , myelin basic protein , isozyme , enzyme , chemistry , biochemistry , dissociation constant , dissociation (chemistry) , myelin , kinetics , biophysics , biology , endocrinology , gene , central nervous system , physics , receptor , quantum mechanics
The charge isoforms (C1‐C5) of bovine myelin basic protein (MBP) were used as substrates for the rat brain enzyme protein carboxylmethyltransferase (PM II). The objective of these experiments was to ascertain whether the kinetic behavior of the MBP isoforms reflected differences in the structures of this molecular family. Initial velocity plots as a function of the MBP‐isoform concentration showed significnt differences ( p > 0.05) among the assayed isoforms except for isoforms C2 and C4. Under the conditions of our experiment all the curves exhibited a consistent sigmoidicity. The kinetic data were best fitted by a model, previously described for the enzyme D‐β‐hydroxybutyrate dehydrogenase, in which two independent sites must be randomly occupied before any catalytic activity can occur. This mechanism is substantially different from that proposed by other investigators for similar PM II enzymes and other substrates. The differences in the rates of isoform carboxylmethylation are largely accounted for by the different apparent dissociation constants K s and is explained on the basis of inherent structural differences among the charge isoforms.