1. An enzymatic activity in bovine brain that catalyzes the reversal of the C-terminal methyl esterification of protein phosphatase 2A
H Xie, S Clarke Biochem Biophys Res Commun. 1994 Sep 30;203(3):1710-5. doi: 10.1006/bbrc.1994.2383.
A novel protein methyltransferase has been recently described that catalyzes the esterification of the C-terminal leucine residue of the catalytic subunit of protein phosphatase 2A in a variety of eucaryotic cells. This reaction can potentially modulate the phosphatase's activity, subunit interactions, or interactions with specific phosphoprotein substrates. We present evidence here that the methylation reaction is reversible and that an enzymatic activity is present in bovine brain cytosol that catalyzes the hydrolysis of the methyl ester. We show that this activity is sensitive to inhibition by the serine-hydrolase inhibitor phenylmethanesulfonyl fluoride but is not affected by the small molecule substrate analog N-acetyl-L-leucine methyl ester. These results suggest that protein methylation and demethylation reactions can be utilized in eucaryotic cells to modulate enzyme activity in a parallel fashion to protein phosphorylation and dephosphorylation reactions.
3. Comparative studies of the specificities of -chymotrypsin and subtilisin BPN'. Studies with flexible and 'locked' substrates
T N Pattabiraman, W B Lawson Biochem J. 1972 Feb;126(3):659-65. doi: 10.1042/bj1260659.
Subtilisin BPN' hydrolysed N-acetyl-l-3-(2-naphthyl)-alanine methyl ester, N-acetyl-l-leucine methyl ester and N-acetyl-l-valine methyl ester, faster than alpha-chymotrypsin. Of eight ;locked' substrates tested, only methyl 5,6-benzindan-2-carboxylate was hydrolysed faster by subtilisin, whereas the other esters were better substrates for chymotrypsin. Compared with the values for chymotrypsin, the stereospecific ratios during the hydrolysis of the optically active locked substrates by subtilisin were decreased by one and two orders of magnitude for bi- and tri-cyclic substrates respectively. The polar groups adjacent to the alpha-carbon atom of locked substrates did not contribute significantly to the reactivity of the more active optical isomers, but had a detrimental effect on the less active antipodes during hydrolysis by both the enzymes. These studies show that the binding site of subtilisin BPN' is longer and broader than that of alpha-chymotrypsin.
