Acid phosphatase isoenzymes possessing phosphotyrosine protein phosphataseactivity from chicken's liver; Some biochemical properties, amino acid composition and protein sequencing

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.