Acid phosphatase isoenzymes possessing phosphotyrosine protein phosphataseactivity from chicken's liver; Some biochemical properties, amino acid composition and protein sequencing
A. Saeed, Acid phosphatase isoenzymes possessing phosphotyrosine protein phosphataseactivity from chicken's liver; Some biochemical properties, amino acid composition and protein sequencing, J CHEM S P, 21(3), 1999, pp. 311-320
Two low Mr acid phosphatase isoenzymes, possessing phosphotyrosine protein
phosphatase activity namely PTPase A and B were purified by affinity chroma
tography to specific activity of 58 and 80 U/mg of protein respectively. Th
e isoenzymes were found to be homogeneous on SDS-PAGE and showed molecular
weight corresponding to 18,000. The enzymes were more active against 4-trif
luoromethylphenyl phosphate, 4-ethylphenyl phosphate, Ar. (CH2)(4). OPO3H2
besides pNPP and phenylphosphate. O-phosphotyrosine was also hydrolyzed at
reasonable rate.
K-m values for PTPase A was smaller than PTPase B against p-nitrophenyl pho
sphate, phenyl phosphate, phosphotyrosine and FMN. FMN seems to be a better
substrate for PTPase B than PTPase A. Fluoride and tartarate have no signi
ficant effect. However, the difference in sensitivity to phosphate, vanadat
e;nd molybdate were observed between PTPase A and B. Zn+2 Mg+2 and Ca+2 all
slightly inhibited PTPase A but not PTPase B. PTPase B was effectively act
ivated by some purine compounds. On the other hand PTPase A was found not t
o be activated by purine compounds but was inhibited by adenine and adenosi
ne.
Attempt to sequence the purified protein was also made by Edman degradation
using Milligen protein sequencer and the works is in progress.