Acid phosphatases in the frog (Rana esculenta) skeletal muscle. Purification and some properties of the low molecular weight enzyme

18 kDa protein tyrosine phosphatase in the ocular lens

Protein tyrosyl phosphorylation and dephosphorylation play essential roles in regulating cellular events such as proliferation and differentiation, and their involvement in the lens development and transparency is also suggested. The level of tyrosine phosphorylation in a given protein is regulated by the opposing actions of protein-tyrosine kinases (Tyr kinases) and protein-tyrosine phosphatases (TyrPases). Recent studies have revealed that some Tyr kinases, such as platelet-derived growth factor receptor and fibroblast growth factor receptor, are present in the lens, however, little is known about TyrPases in the lens. In this study, we found a 18 kDa protein tyrosine phosphatase (18 kDa TyrPase) predominantly present in the ocular lens of various animals. We purified the phosphatase from the lens of chick embryo and characterized its activity.Phosphatase activity was determined in chick embryo, mouse, rabbit and bovine lenses using p -nitrophenyl phosphate (p NPP) as substrate. All lenses examined dephosphorylated p NPP under acidic conditions, and a large portion of the activity resided in a low molecular weight protein, ca. 18 kDa, following high-resolution gel permeation column chromatography. The brain and liver showed high dephosphorylation activities, but most of their activity was present in high molecular weight fractions, unlike that in the lens. The 18 kDa phosphatase was purified from the lens of 17 day old chick embryos to near-homogeneity with two-step rapid chromatography. This phosphatase showed strict substrate specificity for phosphotyrosine and phosphotyrosyl peptides, suggesting that it was a kind of protein tyrosine phosphatases (TyrPases). Several known inhibitors of TyrPases, such as SH blockers, vanadate and phenylarsine oxide, strongly inhibited the enzyme activity. The molecular weight, substrate specificity, and responses to various inhibitors and activators coincide well with those reported for the low molecular weight protein tyrosine phosphatase (LMW-TyrPase), belonging to the TyrPase superfamily. These results suggest that the 18 kDa phosphatase found in the lens is a LMW-TyrPase. The 18 kDa TyrPase is the predominant phosphatase in the ocular lens. It may be involved in regulation of lens cell proliferation, differentiation and/or lens transparency.

ACP1 and human adaptability. 1. Association with common diseases: a case-control study

Human red cell acid phosphatase (ACP1) is a polymorphic enzyme closely related to cytosolic low molecular weight acid phosphatases, a protein family broadly conserved among eukaryotes. Two different functions have been proposed for ACP1: flavin mononucleotide (FMN) phosphatase and phosphotyrosine phosphatase (PTPase). Given that genetic variants of ACP1 activity are common, the enzyme could have a role in regulating a large spectrum of cellular functions and, in turn, disease susceptibility. In the present paper we report a study of ACP1 genetic polymorphism in 1088 normal subjects and in 1267 subjects from the population of Rome admitted to hospital for a number of common diseases. All ACP1 parameters investigated show highly significant differences among samples, suggesting that the enzyme may have a significant role in some of the diseases considered. In particular, consistent associations of ACP1 with developmental disturbances and with hemolytic favism have been observed. In the majority of diseases showing association with ACP1, only one of the two ACP1 isoforms, f and s, is involved, supporting the hypothesis of a functional differentiation between the two enzymatic fractions.

Cloning and characterization of a Saccharomyces cerevisiae gene encoding the low molecular weight protein-tyrosine phosphatase

The low molecular weight protein-tyrosine phosphatase (low M(r) PTPase) is an 18-kDa cytoplasmic enzyme of unknown function that has been previously found in several vertebrates. Using an oligonucleotide probe derived from the active site sequence of the mammalian low M(r) PTPases, a Saccharomyces cerevisiae gene that encodes a homolog of this enzyme was cloned by low stringency hybridization. This gene, LTP1, together with a neighboring gene, TKL1, is shown to be located on the right arm of chromosome XVI. The deduced amino acid sequence of its 161-amino acid residue product shows a 39% average identity with that of the mammalian enzymes. The yeast Ltp1 protein was expressed in Escherichia coli, purified to homogeneity, and shown to possess PTPase activity. The recombinant Ltp1 efficiently hydrolyzes phosphotyrosine and a phosphotyrosine-containing peptide, Tyr531-fyn, but it shows low activity toward phosphoserine and phosphothreonine. The catalytic activity of Ltp1 toward a number of substrates was approximately 30-fold lower than the corresponding values measured for the bovine low M(r) PTPase. However, the yeast enzyme was markedly activated by adenine and some purine nucleosides and nucleotides, including cAMP and cGMP. In the case of adenine, the activity of Ltp1 was increased by approximately 30-fold. The high degree of evolutionary conservation of the low M(r) PTPases implies a significant role for this enzyme. However, neither the disruption of the LTP1 gene nor an approximately 10-fold overexpression of its product in S. cerevisiae caused any apparent phenotypic changes under the conditions tested. No proteins related to Ltp1 could be detected in extracts of the ltp1 null mutant, either by immunoblotting or by gel-filtration analysis accompanied by extended kinetic assays, consistent with the conclusion that LTP1 is the only low M(r) PTPase-encoding gene in S. cerevisiae.

Clinical and biological aspects of acid phosphatase

The identity and genetic origins of the nonspecific orthophosphate monoesterases with an acid pH optimum--the acid phosphatases--are now becoming clear. They form a family of genetically distinct isoenzymes, many of which show significant posttranslational modification. Four true isoenzymes exist. The erythrocytic and lysosomal forms show widespread distribution and are expressed in most cells; in contrast, the prostatic and macrophagic forms have a more limited expression. The erythrocytic and macrophagic forms are distinguished from the others in resisting inhibition by dextrorotatory tartrate. The prostatic form has long been used as a marker for prostatic cancer and the macrophagic forms have been linked with miscellaneous disorders, notably increased osteolysis, Gaucher's disease of spleen, and hairy cell leukemia, whereas the normal levels of intravesical lysosomal acid phosphatase in I cell disease pointed the way toward the mechanisms underlying its intracellular processing.

Activity modulation of the fast and slow isozymes of human cytosolic low-molecular-weight acid phosphatase (ACP1) by purines

The activity modulation of homogeneous isozymes of the human cytosolic M(r) 18,000 acid phosphatase (ACP1) by purines has been investigated. A pronounced difference in the response of fast and slow isozymes of the same genetic type was observed, while identical properties were found for fast isozymes encoded by different alleles (ACP1 X A, B and C), as well as for the corresponding slow isozymes. The catalytic rate constant (kc) of the fast isozymes was increased 5.1-fold by hypoxanthine and decreased 40% by adenine, while the kc of the slow isozymes was unaffected by hypoxanthine but increased 4.6-fold by adenine. This finding and the genetically-determined differences in the relative quantities of the fast and slow isozymes account for the well-known phenotypic differences in activity modulation. The kinetic results strongly indicate that the effector binds to the free enzyme, as well as to the enzyme-substrate complex. Activating effectors showed a higher affinity for the free enzyme than for the enzyme-substrate complex, while the reverse was true with the inhibitor. The results exclude the possibility that effector and substrate bind to the same site of the enzyme; parasteric binding to adjacent sites is suggested.

Acid phosphatases in mammalian tissues. Evidence for the existence of a 57 kDa Zn(2+)-dependent acid phosphatase form

1. A comparative study of multiple forms of acid phosphatase (AcPase) in various organs of mammals was carried out. 2. These studies indicated that the high-molecular weight AcPase is preferentially expressed by tissues which undergo cell proliferation such as epithelial tissues; on the contrary, the low-molecular weight enzyme seems to be characteristic of highly differentiated tissues such as nervous, muscle and blood erythrocytes. 3. The existence of a new AcPase activated by Zn2+ ions was observed in all tissues studied with the exception of erythrocytes. 4. The enzyme shows a molecular weight of 57 kDa, is insensitive to NaF, hydrolyzes p-nitro-phenylphosphate and o-c-phenylphosphate; ATP, a-naphthyl-phosphate and beta-glycerolphosphate are also dephosphorylated.

Human red cell acid phosphatase (ACP1): the primary structure of the two pairs of isozymes encoded by the ACP1*A and ACP1*C alleles

The Af, As, Cf and Cs isozymes encoded by the human red cell acid phosphatase ACP1*A and ACP1*C alleles, respectively, have been sequenced. All four isozymes consist of a single non-glycosylated peptide chain (157 residues), acetylated at the amino-terminal alanine residue. Each f isozyme differs from the corresponding s isozyme over the sequence segment 40-73, while the remaining four-fifth of the molecules are identical. These findings are consistent with results for the Bf and Bs isozymes encoded by the common ACP1*B allele and confirm that the presence of a specific f or s segment is a common property to ACP1 isozymes. This supports our hypothesis that f and s isozymes are generated by alternative splicing of exons in the primary RNA transcript. Cf and Cs are identical in sequence with Bf and Bs, respectively. Thus, the ACP1*B and ACP1*C alleles encode exactly the same pair of isozymes, the only difference at the protein level being the ratio of f and s isozyme. Af and As differ from the Bf and Bs isozymes by a single substitution at residue 105; Arg and Gln, respectively. These observations explain the electrophoretic identity of the B and C isozyme pairs and the higher P(i) of the A isozyme pair.