Rl. Dunten et al., FRACTIONATION AND CHARACTERIZATION OF PROTEIN C-TERMINAL PRENYLCYSTEINE METHYLESTERASE ACTIVITIES FROM RABBIT BRAIN, Biochemical and biophysical research communications, 208(1), 1995, pp. 174-182
Reversible carboxyl methylation of the C-terminal geranylgeranylcystei
ne of G25K may regulate its activity and cellular localization. Brain
homogenates were examined for enzyme activities which hydrolyze the me
thyl ester of [H-3]methyl-G25K to produce [H-3]methanol. Methylesteras
e activity was detected in both soluble and membrane fractions. The so
luble activity was fractionated into at least two distinct activities.
One soluble activity appears to be due to the lysosomal protease, cat
hepsin B, based on sensitivity to certain protease inhibitors, acidic
pH optimum, size, and ability to cleave the peptide substrate N alpha-
CBZ-Arg-Arg-7 amido-4-methylcoumarin. A second soluble activity, assoc
iated with a protein of approximately 25 kDa, exhibits a neutral pH op
timum, insensitivity to protease inhibitors, and inhibition by the est
erase inhibitor, ebelactone B. The membrane fraction contains larger a
mounts of a similar methylesterase that may represent the physiologica
lly relevant form of the enzyme. (C) 1995 Academic Press, Inc.