The human red cell acid phosphatase is a phosphotyrosine protein phosphatase which dephosphorylates the membrane protein band 3

Long Wavelength TCF-Based Fluorescent Probe for the Detection of Alkaline Phosphatase in Live Cells

A long wavelength TCF-based fluorescent probe (TCF-ALP) was developed for the detection of alkaline phosphatase (ALP). ALP-mediated hydrolysis of the phosphate group of TCF-ALP resulted in a significant fluorescence "turn on" (58-fold), which was accompanied by a colorimetric response from yellow to purple. TCF-ALP was cell-permeable, which allowed it to be used to image ALP in HeLa cells. Upon addition of bone morphogenic protein 2, TCF-ALP proved capable of imaging endogenously stimulated ALP in myogenic murine C2C12 cells. Overall, TCF-ALP offers promise as an effective fluorescent/colorimetric probe for evaluating phosphatase activity in clinical assays or live cell systems.

Low molecular weight protein tyrosine phosphatase: Multifaceted functions of an evolutionarily conserved enzyme

Originally identified as a low molecular weight acid phosphatase, LMW-PTP is actually a protein tyrosine phosphatase that acts on many phosphotyrosine-containing cellular proteins that are primarily involved in signal transduction. Differences in sequence, structure, and substrate recognition as well as in subcellular localization in different organisms enable LMW-PTP to exert many different functions. In fact, during evolution, the LMW-PTP structure adapted to perform different catalytic actions depending on the organism type. In bacteria, this enzyme is involved in the biosynthesis of group 1 and 4 capsules, but it is also a virulence factor in pathogenic strains. In yeast, LMW-PTPs dephosphorylate immunophilin Fpr3, a peptidyl-prolyl-cis-trans isomerase member of the protein chaperone family. In humans, LMW-PTP is encoded by the ACP1 gene, which is composed of three different alleles, each encoding two active enzymes produced by alternative RNA splicing. In animals, LMW-PTP dephosphorylates a number of growth factor receptors and modulates their signalling processes. The involvement of LMW-PTP in cancer progression and in insulin receptor regulation as well as its actions as a virulence factor in a number of pathogenic bacterial strains may promote the search for potent, selective and bioavailable LMW-PTP inhibitors.

[Identification of thiamine monophosphate hydrolyzing enzymes in chicken liver]

In animals, thiamine monophosphate (TMP) is an intermediate on the path of thiamine diphosphate, the coenzyme form of vitamin B1, degradation. The enzymes involved in TMP metabolism in animal tissues are not identified hitherto. The aim of this work was to study TMP hydrolysis in chicken liver. Two phosphatases have been found to contribute to TMP hydrolysis in liver homogenate. The first one, possessing a maximal activity at pH 6.0, is soluble, whereas the second one represents a membrane-bound enzyme with a pH optimum of 9.0. Membrane-bound TMPase activity was enhanced 1.7-fold by 5 mM Mg2+ ions and strongly inhibited by levamisole in uncompetitive manner with K1 of 53 μM, indicating the involvement of alkaline phosphatase. An apparent Km of alkaline phosphatase for TMP was calculated from the Hanes plot to be 0.6 mM. The soluble TMPase has an apparent Km of 0.7 mM; this enzyme is Mg2+ independent and insensitive to levamisole. As estimated by gel filtration on a Toyopearl HW-55 column, the soluble enzyme has a molecular mass of 17.8 kDa, TMPase activity being eluted simultaneously with peaks of flavinmononucleotide and p-nitrophenyl phosphatase activity. Thus, TMP appears to be a physiological substrate for a low-molecular weight acid phosphatase, also known as low-molecular-weight protein phosphotyrosine phosphatase.

The presence of a symbiotic bacterium in Strigomonas culicis is related to differential ecto-phosphatase activity and influences the mosquito-protozoa interaction

Strigomonas culicis is a monoxenous trypanosomatid that co-evolves with a symbiotic bacterium in a mutualistic relationship that is characterized by intense metabolic exchanges between both partners. S. culicis infects and colonizes the Aedes aegypti mosquito midgut, reaches its hemocoel and then invades the salivary glands. An artificial aposymbiotic strain is unable to colonize insects, reinforcing the idea that the bacterium influences the protozoan surface composition and cell interaction. Here, we report the characterization of the hydrolytic activity of ecto-phosphatases evaluated in symbiont-bearing and aposymbiotic strains of S. culicis by incubating the protozoa with p-nitrophenyl phosphate (pNPP) at different pH levels, in the presence of phosphatase inhibitors, and with several divalent metals. The symbiont-bearing and aposymbiotic cells differ in their ecto-phosphatase enzymes, based on their activities and specificities. Furthermore, the ability of the protozoan to bind to the mosquito midgut and salivary glands was impaired by ecto-phosphatase inhibition. Taken together, our data suggest that the symbiont influences the host protozoan ecto-phosphatase activity and indicate a possible role of this enzyme during mosquito tissue colonization by S. culicis.

The genetics of feto-placental development: a study of acid phosphatase locus 1 and adenosine deaminase polymorphisms in a consecutive series of newborn infants

BACKGROUND

Acid phosphatase locus 1 and adenosine deaminase locus 1 polymorphisms show cooperative effects on glucose metabolism and immunological functions. The recent observation of cooperation between the two systems on susceptibility to repeated spontaneous miscarriage prompted us to search for possible interactional effects between these genes and the correlation between birth weight and placental weight. Deviation from a balanced development of the feto-placental unit has been found to be associated with perinatal morbidity and mortality and with cardiovascular diseases in adulthood.

METHODS

We examined 400 consecutive newborns from the Caucasian population of Rome. Birth weight, placental weight, and gestational length were registered. Acid phosphatase locus 1 and adenosine deaminase locus 1 phenotypes were determined by starch gel electrophoresis and correlation analysis was performed by SPSS programs. Informed verbal consent to participate in the study was obtained from the mothers.

RESULTS

Highly significant differences in birth weight-placental weight correlations were observed among acid phosphatase locus 1 phenotypes (p = 0.005). The correlation between birth weight and placental weight was markedly elevated in subjects carrying acid phosphatase locus 1 phenotypes with medium-low F isoform concentration (A, CA and CB phenotypes) compared to those carrying acid phosphatase locus 1 phenotypes with medium-high F isoform concentration (BA and B phenotypes) (p = 0.002). Environmental and developmental variables were found to exert a significant effect on birth weight-placental weight correlation in subjects with medium-high F isoform concentrations, but only a marginal effect was observed in those with medium-low F isoform concentrations. The correlation between birth weight and placental weight is higher among carriers of the adenosine deaminase locus 1 allele*2, which is associated with low activity, than in homozygous adenosine deaminase locus 1 phenotype 1 carriers (p = 0.04). The two systems show a cooperative effect on the correlation between birth weight and placental weight: the highest value is observed in newborns carrying adenosine deaminase locus 1 allele*2 and acid phosphatase locus 1 phenotypes with medium-low F isoform concentration (p = 0.005).

CONCLUSION

These data suggest that zygotes with low adenosine deaminase locus 1 activity and low F activity may experience the most favourable intrauterine conditions for a balanced development of the feto-placental unit.

Effect of glycyrrhetinic acid on membrane band 3 in human erythrocytes

Glycyrrhetinic acid (GA) is a hydrolytic product of the triterpene glycoside of glycyrrhizic acid, one of the main constituents of licorice root, which has long been studied, due to its several biological and endocrine properties. In this paper, GA was tested on human erythrocytes, and GA-induced alterations were compared with those caused by diamide, a mild oxidant inducing well-characterized cell/membrane alterations, and n-ethylmaleimide (NEM), as alkylating agent. In order to verify the biochemical steps underlying the action of GA, band 3 Tyr-phosphorylation level, enzyme recruitment and band 3 clustering in cells pre-incubated with GA before diamide treatment were all examined. Results show that GA, in a dose-dependent manner, prevents both diamide and NEM-induced band 3 Tyr-phosphorylation, but not GSH decrease caused by both compounds. In addition, diamide-induced band 3 clustering and IgG binding to altered cells were also completely reversed by GA pre-treatment. Also, when membrane sensitivity toward proteolytic digestion was tested, GA-treated cells showed high resistance to proteolysis. In conclusion, in human erythrocytes, GA is proposed to strengthen membrane integrity against both oxidative and proteolytic damage.

The effects of genetic and seasonal factors on reproductive success

OBJECTIVE

To search for possible effects of two polymorphisms and of the solar cycle of illumination on reproductive success.

DESIGN

Study of haptoglobin (Hp) and ACP1 polymorphisms in consecutive puerperae and analysis of phenotype distribution in relation to time of conception.

SETTING

The Maternity Department of Penne Hospital, Penne, Italy.

PATIENT(S)

Three hundred sixty-eight consecutive healthy pueperae from the Caucasian population.

RESULT(S)

The distribution of Hp and ACP1 phenotypes depends on the phase of the solar cycle at conception. Women homozygous for Hp with low ACP1 activity are more likely to conceive in the first part of the year. Women heterozygous for Hp with medium-high ACP1 activity are more likely to conceive in the last part of the year.

CONCLUSION(S)

In the first months of the year there is a steady increase in solar illumination, and this phase corresponds to the best period for reproduction in most plants and animals. This period is also the coldest in the Italian latitudes. Although humans are not seasonal breeders, it is possible that women having a genetic background best adapted to the metabolic demand of the cold period of the year will respond better to reproductive stimuli, resulting in a higher probability of conceiving in the first part of the year.

Repeated spontaneous abortion. Cooperative effects of ADA and ACP1 genetic polymorphisms

PROBLEM

In consideration of the effect of adenosine deaminase (ADA) and ACP1 (a low-molecular-weight protein tyrosine phosphatase) on T-cell receptor activity, we have analysed the joint distribution of these polymorphisms in a sample of women with primary repeated spontaneous abortion (RSA) to search for possible interactive effects on susceptibility to RSA.

METHOD OF STUDY

ACP1 and ADA phenotypes were determined in 170 women with primary RSA in 79 healthy consecutive puerperae and in 160 female newborns from the Caucasian population of Rome and in 357 healthy consecutive puerperae from the Caucasian population of Penne. Chi-square test of independence and three way contingency table analysis by a log-linear model were performed.

RESULTS

Women with low-ADA activity and high-ACP1 activity show the lowest susceptibility to RSA. Women with high-ADA activity and low-ACP1 activity, on the contrary, show the highest susceptibility to RSA and also the highest incidence of auto antibodies and of A blood group incompatibility.

CONCLUSION

The data are in agreement with those expected on the basis of the effects of ACP1 and ADA genetic variability on T-cell receptor activity and suggest a cooperative effect of the two polymorphic systems in the susceptibility/resistance to repeated spontaneous abortion.

ACP1 and offspring sex ratio in smoking puerperae: a study at population level

BACKGROUND

Data from previous study by our group suggest that in smoking women sex ratio of offspring is higher in newborns carrying ACP1C allele than in other ACP1 genotypes, suggesting that differences observed among human population concerning the effect of smoking may depend in part on this genetic factor.

OBJECTIVES

In order to further explore this issue we have studied another population and have analysed the relationship between sex ratio and ACP1C gene frequency at population level.

METHODS

The analysis includes 719 consecutive births from Central Italy considered in a previous paper and 5510 consecutive births from Sardinia. Data from English and Japanese populations have also been considered in the analysis.

RESULTS

Among newborns not carrying ACP1C there is a decrease of SR among the offspring of smoking mothers, while among newborns carrying the ACP1C allele there is an increase of SR among the offspring of smoking mothers relative to non-smoking mothers. Considering Sardinian, Italian, English and Japanese population there is a linear positive relationship between C allele frequency and SR in smoking mothers.

CONCLUSIONS

The present observation suggests an interaction between smoking and ACP1 regarding their effects on sex ratio, by which the presence of the ACP1C allele appears to counteract the effect of smoking. This suggests that genetic background may modify the effects of toxic environmental factors on gamete production and functionality and/or on intrauterine survival.

ACP1 and Th Class of Immunological Disease: Evidence of Interaction with Gender

BACKGROUND

Data collected by our group in the past years indicate a relationship between ACP1 genetic polymorphism and susceptibility/resistance to immunological diseases. Recent observations suggest that through modulation of ZAP-70 activity, the enzyme may influence T cell activation. In view of the current interest in gender differences in autoimmune diseases we reviewed our data to enlighten possible effects of gender on the relationship between ACP1 and class of immunological disease.

METHODS

We studied three samples of subjects with allergic disorders of a total of 299 subjects, 71 subjects with Crohn's disease and 188 children with type 1 diabetes. Three-way contingency tables were analyzed by a log linear model and two-way contingency tables by chi(2) test.

RESULTS

There is an association between ACP1 and allergy (Th2 class) that depends on gender: the presence of the ACP1*A allele seems to make females more susceptible to allergic manifestations as compared to males. ACP1 is also associated with Crohn's disease and type 1 diabetes: the relationship between this class (Th1) of immunological diseases and ACP1 depends on gender. The presence of *A allele seems to make females less susceptible to this class of diseases as compared to males.

CONCLUSIONS

The ACP1*A allele which is associated with low ACP1 activity appears responsible for a complex relationship involving gender, ACP1 and Th1/Th2 orientation. Low ACP1 activity influencing ZAP-70 activity and in turn T cell activation seems to have opposite effects on Th1/Th2 orientation depending on gender.

SHP-1 Tyrosine Phosphatase in Human Erythrocytes

SHP-1 is a SH2-domain containing protein Tyr-phosphatase expressed in hematopoietic cell lines, which is hypothesized to play a negative role in signal transduction. In human erythrocytes, the phospho-Tyr level of proteins, mainly transmembrane band 3, is closely controlled by the antithetic activity of Tyr-protein kinases and phosphatases, resulting in a dephosphorylated state. Only after particular stimuli, as with oxidizing agents, diamide or pervanadate, or thiol alkylating compound, N-ethyl maleimide (NEM), Tyr-phosphorylation of band 3 can be triggered, inhibiting Tyr-phosphatase action and inducing erythrocyte membrane reorganization. We demonstrate that, in human erythrocytes, SHP-1 is present in membranes from resting cells, but in 5% of the protein amount. Interestingly, this amount increases up to threefold following NEM treatment of intact cells, whereas diamide and pervanadate do not alter the normal protein location. In addition, SHP-1 translocation from cytosol to membrane is not affected by band 3 P-Tyr level, because it is not mediated by the SH2-P-Tyr recruitment mechanism, and localizes into the cytoskeletal compartment. Band 3 is the target of SHP-1, which dephosphorylates Tyr 8, 21, and 904. These findings support the idea that, in human erythrocytes, the normal level of Tyr-phosphorylation of membrane protein, mainly band 3, must be downregulated. We hypothesize that the presence of both SHP-2 and SHP-1 ensures band 3 dephosphorylation in different conditions: SHP-2, through interaction of its SH2 domain/s to P-Tyr protein, is regulated by the band 3 Tyr-phosphorylation level; SHP-1 may be involved by simple membrane rearrangement.

Characterization of ecto-phosphatase activities of Trypanosoma cruzi: a comparative study between Colombiana and Y strains

The etiological agent of Chagas disease, Trypanosoma cruzi, is consisted of two phylogenetic lineages. Using live epimastigotes, in this study we have characterized ecto-phosphatase activities of two strains of T. cruzi, one (Y strain) is a member of group T. cruzi I and the other (Colombiana) is a member of group T. cruzi II. About one-third of the total ecto-phosphatase activity from the Y strain was Mg(2+)-dependent, but no such activity was observed with Colombiana. The level of Mg(2+)-independent activity was dramatically different in the two strains, with Colombiana showing more than 15-fold higher activity. Experiments using classical inhibitors of acid phosphatases, as well as inhibitors of phosphotyrosine phosphatase, showed a decrease in these phosphatase activities, with different patterns of inhibition. The Mg(2+)-independent activities of the Colombiana and Y strains decreased inversely with pH, varying from 6.5 to 8.0. On the other hand, the Mg(2+)-dependent activity of the Y strain increased concomitantly with the increase in pH in the same range.

Feto-maternal ACP1 activity ratio and intrauterine survival

OBJECTIVE

Genetic differences in the activity of phosphotyrosine phosphatases between mother and embryo could result in a differential activation of signals induced by growth factors in the two sides of placenta. Previous observations suggest that this may have important effects on intrauterine development and survival. The aim of the present study is to confirm previous observations and show new data.

STUDY DESIGN

We have studied 573 mother/newborn pairs, 169 wife/husband couples with repeated spontaneous abortion and 34 fertile wife/husband couples

RESULTS

In mother/newborn pairs, the analysis of joint mother/infant ACP1 distribution has shown a deficit of pairs with the mother having low ACP1 S isoform concentration and the infant having high S isoform concentration, and an excess of pairs with the mother having high S isoform concentration and the infant having low S isoform concentration. In RSA couples there is an excess of couples in which the wife has low S isoform concentration and the husband has high S isoform concentration and a deficit of couples in which the wife has high S isoform concentration and the husband has low S isoform concentration. In fertile couples the pattern is reversed.

CONCLUSION

The data suggest that when the mother to fetus S isoform concentration ratio is in favour of the mother, the probability of survival of the fetus is greater than in the opposite situation.

Regulation of human erythrocyte metabolism by insulin: cellular distribution of 6-phosphofructo-1-kinase and its implication for red blood cell function

Human erythrocytes are highly specialized cells whose function is oxygen transport. These cells' sole metabolic source of energy is the fermentation of glucose via glycolysis. They contain an active insulin receptor and respond to insulin by increasing phosphorylation of tyrosine residues in several proteins. However, no metabolic effects have yet been associated with activation of this receptor in human erythrocytes. Here, we show that insulin increases the rate of glycolysis in human erythrocytes. Lactate production increased 56 and 173% in the presence of 10 and 100 nM insulin, respectively. A higher insulin concentration (1000 nM) partially reversed the stimulation of glycolysis. These effects occur through activation of the key glycolytic enzyme 6-phosphofructo-1-kinase, which exhibits the same pattern of modulation by insulin as seen for glycolytic flux. This modulation also occurs physiologically since ex vivo experiments revealed 50% stimulation of 6-phosphofructo-1-kinase (PFK) activity following a high carbohydrate meal. Insulin increases phosphorylation of PFK and redistributes the enzyme in red blood cells, causing it to detach from the erythrocyte membrane: upon insulin stimulation, the amount of enzyme associated with the plasma decreases by 86%. Detachment is a common mechanism of enzyme activation. As a consequence, insulin prevents up to 68% of red cells hemolysis. These results show that insulin regulates erythrocyte glycolysis and viability and suggest that this regulation is associated to other erythrocyte functions such as oxygen transport. Finally, we suggest that this regulatory mechanism might be compromised in patients with diabetes mellitus.

Effector-induced Syk-mediated phosphorylation in human erythrocytes

Band 3 (AE1), the most prominent polypeptide of the human erythrocyte membrane, becomes heavily tyrosine phosphorylated following treatment of intact cells with protein tyrosine phosphatase inhibitors such as diamide, pervanadate, vanadate, or N-ethylmaleimide (NEM). The mechanism underlying this tyrosine phosphorylation is thought to involve the sequential action of two protein tyrosine kinases, Syk (p72syk) and Lyn (p53/56lyn). While Lyn catalysed phosphorylation appears to be strictly dependent on prior phosphorylation of Tyr8 and 21 of band 3 by Syk, little is known about the mechanism of induction of Syk phosphorylation. Data presented here show that both the fraction of Syk that associates with the membrane and the extent of phosphorylation of band 3 differ in response to the above inhibitors. While diamide and NEM stimulate syk translocation to the membrane during their induction of band 3 tyrosine phosphorylation, pervanadate and vanadate induce no change in kinase distribution. Moreover, diamide and NEM-induced Syk recruitment to the membrane are phosphotyrosine independent and involve their preferential association with Triton X-100-insoluble membrane skeletons. Together these data reveal a complex process controlling the association and catalytic activity of protein tyrosine kinases syk and lyn with the human erythrocyte membrane.

Type 2 diabetes and the genetics of signal transduction: a study of interaction between adenosine deaminase and acid phosphatase locus 1 polymorphisms

Acid phosphatase locus 1 (ACP1) is a highly polymorphic enzyme that has an important role in flavoenzyme activity and in the control of insulin receptor activity and band 3 protein phosphorylation status. Adenosine deaminase (ADA) is a polymorphic enzyme that catalyses the irreversible deamination of adenosine to inosine and has an important role in regulating adenosine concentration. Based on the hypothesis that ACP1 counteracts insulin signaling by dephosphorylating the insulin receptor and that adenosine has an anti-insulin action, we reasoned that low ACP1 activity (low dephosphorylating action on insulin receptor) when associated with high ADA activity (low adenosine concentration) would result in a cumulative effect towards an increased glucose tolerance. On the contrary, high ACP1 activity when associated with low ADA activity would result in a cumulative effect towards a decreased glucose tolerance. A total of 280 adult subjects with type 2 diabetes from the population of Penne (Italy) were studied. There was a nonsignificant trend toward an increase in the proportion of subjects with the complex type with high ACP1 activity and low ADA activity (ie, *B/*B; *A/*C; *B/*C; *C/*C//ADA*1/*2 and *2/*2) in type 2 diabetes relative to that observed in newborn infants from the same population. High ACP1 activity/low ADA activity joint genotype was positively associated with high glycemic levels and with high body mass index (BMI) values. Low ACP1 activity/high ADA activity joint genotype was also positively associated with dyslipidemia. These findings suggest that both ACP1 and ADA contribute to the clinical manifestations of type 2 diabetes and probably also have a marginal influence on susceptibility to the disease. Both additive and epistatic interactions between the 2 systems seem to be operative.

Differential sorting of tyrosine kinases and phosphotyrosine phosphatases acting on band 3 during vesiculation of human erythrocytes

One of the most intensively studied post-translational modifications of erythrocyte proteins is the phosphorylation of tyrosine residues of band 3, which is strictly regulated in vivo by PTKs (protein-tyrosine kinases) and PTPs (protein-phosphotyrosine phosphatases). Two PTKs (p72(syk) and p56/53(lyn)) and two PTP activities (PTP1B and SHPTP-2) have been immunologically identified so far in mature human erythrocytes. We have shown previously that band 3 undergoes tyrosine phosphorylation upon a decrease in cell volume, as occurs when erythrocytes treated with Ca(2+)/Ca(2+) ionophore (A23187) lose KCl and release microvesicles. Similar levels of band 3 tyrosine phosphorylation in vesicles and in the parent cells are induced by this treatment. However, we have found that tyrosine phosphorylation of band 3 in vesicles is more stable than in whole erythrocytes. Examination of how the identified PTPs and PTKs are partitioned between the vesicles and the remnant cells during vesiculation reveals that PTP1B, unlike the PTKs, is retained entirely in the parent cell compartment. Since a tight association between PTP1B and band 3 has been documented previously, we have investigated the partitioning of PTP1B and band 3 between the membrane and the membrane-skeletal fractions prepared from resting or Ca(2+)/A23187-treated cells. Our results rule out the possibility that the preferential retention of PTP1B within the cell was due to an increase in the amount of membrane-skeleton-associated band 3 (and of PTP1B) during the release of spectrin-free vesicles, suggesting a more complex modality of interaction of PTP1B with band 3 in the erythrocyte membrane. Analysis of erythrocytes of different cell ages revealed that PTP1B, unlike the other enzymes examined, was quantitatively conserved during erythrocyte aging. This suggests important roles for the down-regulation of tyrosine phosphorylation of band 3 in erythrocyte physiology, and for vesiculation as a mechanism of human erythrocyte senescence.

Smoking and the genetics of signal transduction: an association study on retinopathy in type 1 diabetes

BACKGROUND

Recent studies suggest a complex association between smoking and retinopathy that probably depends on the interaction between many variables. We have reported an association between ACP1 phenotype and retinopathy in type 1 diabetes. Additionally, the deleterious effects of smoking on intrauterine growth are dependent on ACP1, a low-molecular-weight tyrosine phosphatase that modifies signal transduction. We examine here the interaction between smoking and ACP1 as a mediator of susceptibility to diabetic retinopathy in a sample of puerperae with type 1 diabetes.

SUBJECTS AND METHODS

Seventy-eight women who had just delivered live infants were studied. ACP1 phenotype was determined by starch gel electrophoresis. Three-way contingency tables were analyzed.

RESULTS

There is a significant epistatic interaction between smoking and ACP1 phenotype concerning their effects on retinopathy. In subjects with low ACP1 activity, frequency of retinopathy was slightly higher in smokers than in nonsmokers. However, in subjects with medium-high ACP1 activity, frequency of retinopathy was significantly lower in smokers than in nonsmokers. A logistic regression analysis using retinopathy as the dependent variable revealed that smoking, ACP1, and ACP1 by smoking interaction, as well as the interaction between smoking and age of the women, are the most robust predictors of retinopathy.

CONCLUSIONS

The effect of smoking on retinopathy in women with type 1 diabetes depends on many variables, which supports the hypothesis of complex interactions between smoking and other variables in the pathogenesis of this disease. Variability of genetic factors involved in signal transduction may affect endothelium proliferation through the regulation of growth factors and through regulation of glycemic levels. Because cigarette smoke influences signal transduction, its impact on diabetic retinopathy may be mediated by ACP1.

Deoxygenation of sickle cells stimulates Syk tyrosine kinase and inhibits a membrane tyrosine phosphatase

Polymerization of hemoglobin S in sickle red cells, in deoxygenated conditions, is associated with K+ loss and cellular dehydration. It was previously reported that deoxygenation of sickle cells increases protein tyrosine kinase (PTK) activity and band 3 tyrosine phosphorylation and that PTK inhibitors reduce cell dehydration. Here, the study investigates which PTKs are involved and the mechanism of their activation. Deoxygenation of sickle cells induced a 2-fold increase in Syk activity, measured by autophosphorylation in immune complex assays, but had no effect on Lyn. Syk was not stimulated by deoxygenation of normal red cells, and stimulation was partly reversible on reoxygenation of sickle cells. Syk activation was independent of the increase in intracellular Ca++ and Mg2+ associated with deoxygenation. Lectins that promote glycophorin or band 3 aggregation did not activate Syk. In parallel to Syk stimulation, deoxygenation of sickle cells, but not of normal red cells, decreased the activity of both membrane-associated protein tyrosine phosphatase (PTPs) and membrane protein thiol content. In vitro pretreatment of Syk immune complexes with membrane PTP inhibited Syk autophosphorylation. It is suggested that Syk activation in vivo could be mediated by PTP inhibition, itself resulting from thiol oxidation, as PTPs are known to be inhibited by oxidants. Altogether these data indicate that Syk could be involved in the mechanisms leading to sickle cell dehydration.

ACP1 and human adaptability: association with past malarial morbidity in the Sardinian population

Acid Phosphatase locus 1 (ACP1) is a polymorphic enzyme controlled by a locus on chromosome 2 with three common codominant alleles: *A, *B, and *C. ACP1 shows two major isoforms, F and S. The ratio of their concentration differs markedly among genotypes. Two functions have been proposed for the enzyme: flavin-mononucleotide phosphatase and tyrosine phosphatase activity. An association between ACP1 polymorphism and past malarial morbidity in Sardinia and the Po Valley has been described. Genetic polymorphisms could contribute to natural resistance or susceptibility to the disease. On the other hand, malaria pressure may select for genes that increase susceptibility to common diseases of modern civilization. Thus, the association between ACP1 and malaria in Sardinia in the light of recent understanding of the function of ACP1 and the molecular basis of malaria pathophysiology, especially aspects of the structure of band 3 protein (B3P) and the role of cytokines have been revisited. There is a significant negative correlation between ACP1 S isoform concentration, directly related to the ACP1*C allele, and past malarial morbidity in Sardinia. Populations subjected in the past to a heavy malarial burden show, at present, a lower concentration of the S isoform compared to a nearby malaria-free population, suggesting that genotypes with high S isoform concentration have been subjected to negative selection in a malarial environment. Correlation analysis and analysis of the joint G-6-PD/ACP1 distribution suggest that the relationship between past endemic malaria and the S isoform has not been mediated by glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, thus pointing to a direct effect of malaria on ACP1.

Characterization of ectophosphatase activities in trypanosomatid parasites of plants

ABSTRACT In the present work ectophosphatase activities of three trypanosomatid parasites of plants were characterized using intact cells. Phytomonas françai, Phytomonas mcgheei, and Herpetomonas sp. hydrolyzed p-nitro-phenylphosphate at a rate of 5.40, 7.28, and 25.58 nmol Pi/mg of protein per min, respectively. Experiments using classical inhibitors of acid phosphatases such as sodium orthovanadate (NaVO(3)) and sodium fluoride (NaF) showed a decrease in phosphatase activities. Lithium fluoride (LiF) and aluminum chloride (AlCl(3)) were also used. Although AlCl3 had no effect, LiF was able to promote a decrease in the phosphatase activities. Interestingly, the inhibition caused by LiF was enhanced by the addition of AlCl3 during the reaction, probably due to the formation of fluoroaluminate complexes. This effect was confirmed by cytochemical analysis. In this assay, electron-dense cerium phosphate deposits were visualized on the external surface of the three parasites.

Adenosine deaminase-acid phosphatase association and the environment: A study in a continental Italian population

Three hundred fifty newborns from Rome and 351 from Penne were studied in continental Italy. Medium high altitude above sea level and cold winters characterize the area of Penne, while low altitude and very mild winters characterize the area of Rome. An effect of environmental conditions on the association between adenosine deaminase (ADA) and acid phosphatase (ACP1), previously shown in Sardinia, has been confirmed in continental Italy. When compared with expected independent assortment, the proportion of ACP1*A/*A carrying the ADA*2 allele is lower than expected in the lowlands and higher than expected in highlands. In continental Italy there is an interaction among ACP1-ADA genotype, season of conception, and locality. The excess of *A/*A newborns carrying the ADA*2 allele is present only among those conceived in the first half of the year (January-June). Among newborns in Penne conceived in the Spring, the proportion of those with *A/*A genotype is increased and these infants show decreased intrauterine growth. The present data suggest that ADA and ACP1 interact during intrauterine life with effects on development and survival and that such effects are dependent on local environment and season of conception. Am. J. Hum. Biol. 12:214-220, 2000. Copyright 2000 Wiley-Liss, Inc.

Insulin and high glucose modulation of phosphatase and reductase enzymes in the human erythrocytes: a comparative analysis in normal and diabetic states

The ability of insulin to influence activities of various protein kinases and protein phosphatases, that are thought to mediate insulin action, are limited in patients with insulin resistance. Because numerous responses to insulin are affected, we undertook studies to determine whether protein tyrosine phosphatases (PTPs) activities are altered in patients with diabetes syndrome. In order to evaluate abnormal PTP activities, we done a comparative study using erythrocytes from normal and diabetic patients. We determined the activity of the cytosolic acid PTP in basal and insulin-dependent states. Mean basal PTP activities, were found to be significantly higher in diabetics than in normal subjects (type 1 diabetics: 0.36 +/- 0.01 vs 0.28 +/- 0.01 mmol p-nitrophenolate/h per g hemoglobin (Hb), P < 0.001; type 2 diabetics: 0.35 +/- 0.01 vs 0.28 +/- 0.01 mmol p-nitrophenolate/h per g Hb, P < 0.001). Insulin, at concentrations above physiological levels (1 mIU/ml), inhibited the PTP activities in erythrocytes from normal subjects (-15 +/- 4.1%, P < 0.01). Insulin could also modulate glycolysis, probably as a consequence of receptor tyrosine kinase activation, inducing phosphorylation of protein band 3 and hence the release of glycolytic enzymes. We have previously reported that a reductase enzyme in human erythrocytes is dependent on glycolysis being significantly activated (+28 +/- 3.1%, P < 0.001) by high insulin levels (1 mIU/ml). Mean basal reductase activities were found to be significantly lower in diabetics than in normal subjects (type 1 diabetics: 0.77 +/- 0.03 vs 0.97 +/- 0.02 mmol ferrocyanide/20 min per l cells, P < 0.001; type 2 diabetics: 0.77 +/- 0.04 vs 0.97 +/- 0.02 mmol ferrocyanide/20 min per l cells, P < 0.001), indicating altered erythrocyte metabolism in the diabetic patients. High glucose levels were used to mimic hyperglycemia condition, using erythrocytes from normal subjects. At 30 mM glucose, erythrocytic phosphatase activity was stimulated (+32 +/- 4.2%, P < 0.0001), although no effect was observed on the reductase enzyme at the same glucose levels. Results indicated that diabetic disorders appear to be associated with quantitative alterations of erythrocyte acid phosphatase activity and other enzymes that depend on the glycolytic rate (reductase). The overall data suggest that erythrocyte acid phosphatase may have a role in the modulation of glycolytic rates through the control of insulin receptor phosphorylation.

Association between cytosolic low molecular weight phosphotyrosine-phosphatase and malaria--a possible mechanism

Cytosolic low molecular weight phosphotyrosine-phosphatase shows dephosphorylating activity of the band 3 protein. Increased phosphorylation of this protein increases membrane rigidity and resistance to invasion of red blood cells by malarial parasites. This observation may explain the negative association previously reported by our group between the high activity *C allele of cytosolic low molecular weight phosphotyrosine-phosphatase and past malarial morbidity.

Increased tyrosine phosphorylation of band 3 in hemoglobinopathies

In order to investigate the tyrosine phosphorylation of band 3, we performed immunoblotting of intact red cells using anti-phosphotyrosine antibody of 21 patients with sickle cell disorders (11 SS, 5 Sbeta, 5 SC), 7 patients with beta thalassemias (5 beta thal intermedia, 2 deltabeta thal), 10 normal controls, and 1 patient with hereditary spherocytosis. They had not received transfusion for the last 4 months and all were clinically stable. Our results showed an increased tyrosine phosphorylation of two proteins, in the 100 and 80 kD regions, in sickle cell and beta-thalassemic red cells when compared to the normal controls and to the patient with hereditary spherocytosis. Immunoprecipitation of the lysed red cells with anti-band 3 antibody and immunoblotting with anti-phosphotyrosine antibody confirmed that the 100 kD tyrosine phosphorylated protein was band 3. In the sickle cell disease group, the band 3 tyrosine phosphorylation varied from 2- to 10-fold increase compared to control (x +/- SD; SS = 7.8- +/- 2.7-fold; SC = 3.8- +/- 1.3-fold; Sbeta = 5.2- +/- 2.0-fold). It was also higher in the beta-thalassemic group (beta-thal = 4.3- +/- 3.7-fold). There was no significant difference in tyrosine phosphorylation among the various groups tested, except when we compared the phosphorylation in intact red cells of patients with sickle cell anemia and hemoglobinopathy SC (U = 6, P < 0.02). The tyrosine phosphorylation of band 3 was increased in hemoglobinopathies even in the absence of high reticulocyte count. At least two mechanisms might be involved in the increased tyrosine phosphorylation of band 3 in these hemoglobin disorders, probably related to the endogenous reactive oxygen intermediates generated by the abnormal erythrocyte: an inhibition of protein tyrosine phosphatase activity or an activation of the protein tyrosine kinase p72syk.

Phosphotyrosine protein phosphatases and diabetic pregnancy: an association between low molecular weight acid phosphatase and degree of glycemic control

Low molecular weight acid phosphatase encoded by the highly polymorphic locus ACP1 is a member of the protein-tyrosin phosphatase family (PTPases) which plays an essential role in the control of receptor signalling through phosphotyrosine pathways. Recent experiments have shown that purified rat liver ACP, corresponding to human ACP1, is able to hydrolyze a phosphotyrosine-containing synthetic peptide corresponding to the 1146-1158 sequence of the human insulin receptor, and shows a high affinity for it. This prompted us to analyze the degree of glycemic control in relation to ACP1 genetic variability in a sample of 214 diabetic pregnant women including IDDM, NIDDM and gestational diabetes. The ACP1 genotype was also determined in 482 non-diabetic pregnant women. In diabetic women glycemic levels in the last trimester of pregnancy appear to be significantly associated with the ACP1 genotype, and correlate positively with ACP1 enzymatic activity. The data suggest that quantitative variations of ACP1 may influence the clinical manifestations of diabetic disorders, and call for further studies on the role of this enzyme in the modulation of insulin-receptor phosphotyrosine pathways.

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.

Expression, purification and kinetic behaviour of fission yeast low M(r) protein-tyrosine phosphatase

A gene named stp1+, coding for a 17.5-kDa protein, that rescues cdc25-22 when overexpressed, has been previously isolated from fission yeast. Here we describe the expression and purification of Stp1 protein as a fusion with the glutathione S-transferase in E. coli and its kinetic characterisation. Stp1 deduced protein sequence shows an high homology to members of a class of cytosolic low M(r) protein phosphatase previously known to exist only in mammalian species. Stp1 has a kinetic behaviour that appears to be intermediate with respect to the two isoenzymatic forms of low M(r) protein tyrosine phosphatases present in mammalian tissues. These differing kinetic characteristics are mainly due to the sequence 45-56 that is spatially close to the active site pocket.

Fluorescence resolution of the intrinsic tryptophan residues of bovine protein tyrosyl phosphatase

Fluorescence steady-state and lifetime measurements have been performed that permit the differentiation of the 2 intrinsic tryptophan residues in bovine low molecular weight phosphotyrosyl protein phosphatase (BPTP). Spectral information was obtained by use of two single-tryptophan mutant proteins, W39F and W49F, and the double mutant protein W39,49F. Fluorescence measurements show that Trp39 is characterized by a large blue shift, a low quantum yield, and a shorter mean lifetime compared to Trp49. Solute fluorescence quenching studies of W39F reveal that Trp49 is highly exposed to the aqueous environment. In contrast, Trp39 is situated within a hydrophobic core and is only partially accessible to quenching agents such as acrylamide, iodide ion, and cesium ion. The fluorescence contributions of Trp39 and Trp49 are additive, and their sum is equivalent to that observed for wild type BPTP. Calculated intramolecular distances between Trp39 or Trp49 and a 5-[[(acetylamino)-ethyl]amino]naphthalene-1- sulfonate group covalently bound at Cys12 or Cys17 of the respective protein mutants, place Trp49 within 10 A and Trp39 at least 20 A from the active site. The fluorescence decay of the single tryptophan mutants and, surprisingly, wild type BPTP were each adequately fitted as biexponentials. The latter is a consequence of the imprecision involved in determining actual minima in a three- and four-exponential fitting. Comparison of quenching results of wild type BPTP with those of the single tryptophan mutant proteins indicates that minor fluorescence components, easily resolved using a biexponential fitting for the mutant proteins, are unresolvable for wild type BPTP. These minor components skewed the weighted magnitudes and induced perturbations in lifetimes for the tryptophan fluorescence of wild type BPTP, which directly influenced the calculated values of Ksv and kq.

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.

Haptoglobin development in newborn infants from diabetic mothers

Haptoglobin (Hp) development during the neonatal period has been studied in 325 newborn infants from normal pregnancies and in 242 infants from diabetic mothers. In infants from diabetic mothers Hp development is delayed as compared to infants from normal pregnancies. This delay is associated with a change in the pattern of relationship between Hp development and the polymorphism of acid phosphatase (ACP1) (an enzyme which shows phosphotyrosine phosphatase (PTPase) activity). In infants from normal pregnancies who show ACP1 phenotypes with the highest activity, the appearance of Hp is accelerated as compared to other infants. In contrast, infants from diabetic pregnancies who have ACP1 phenotypes with the highest activity, show delayed Hp development.

Backbone 1H, 13C, and 15N assignments and secondary structure of bovine low molecular weight phosphotyrosyl protein phosphatase

Phosphotyrosyl protein phosphatases play an important role in mediating cellular signal transduction; yet three-dimensional structures of this important class of proteins have not been reported. We present the sequence-specific 1H, 13C, and 15N backbone assignments for the low molecular weight bovine heart phosphotyrosyl protein phosphatase (BHPTPase) (157 residues, 17,900). The assignments were obtained from a combination of double- and triple-resonance multidimensional NMR experiments. From these assignments, the secondary structure of BHPTPase was determined from an analysis of NOE patterns, 3JHNH alpha coupling constants, 13C alpha and 13CO chemical shifts, and amide 1H exchange rates. BHPTPase was found to consist of a four-stranded parallel beta-sheet (residues K6-C12, W39-A45, Y87-M91, and K112-L116), four alpha-helices (residues I21-D32, R58-G67, S94-N104, and D135-R157), and one stretch of beta 10-helix (residues K79-F85). The secondary structure is characteristic of the beta alpha beta structural motif. The secondary structure elements identified in this study are consistent with previous chemical and mutagenesis studies of BHPTPase structure.

The role of His66 and His72 in the reaction mechanism of bovine liver low-M(r) phosphotyrosine protein phosphatase

Site-directed mutagenesis of a synthetic gene coding for low-M(r) phosphotyrosine protein phosphatase from bovine liver has been carried out. The two histidine residues in the enzyme have been mutated to glutamine; both single and double mutants were produced. The mutated and non-mutated sequences have been expressed in Escherichia coli as fusion proteins, in which the low-M(r) phosphotyrosine protein phosphatase was linked to the C-terminal end of the maltose-binding protein. The fusion enzymes were easily purified by single-step affinity chromatography. The mutants were studied for their kinetic properties. Both single mutants showed decreased kcat. values (30 and 7% residual activities for His66 and His72 respectively), and alterations of the Ki values relative to four-competitive inhibitors were observed. The kinetic mechanism of p-nitrophenyl phosphate hydrolysis in the presence of both single mutants was determined and compared with that of the non-mutated enzyme. The rate-determining step of the catalytic process of the His66-->Gln mutant was the same as that found for non-mutated enzyme, whereas for the His72-->Gln mutant, both the kinetic constant of the step that causes the formation of a phosphoenzyme covalent intermediate, and the kinetic constant of the step that causes the dephosphorylation of the enzyme covalent intermediate, determined the kcat. value. This observation was confirmed by phosphoenzyme covalent intermediate trapping experiments. The participation of both histidine residues (His66 and His72) at the active site is strongly suggested by the results of diethyl pyrocarbonate inactivation of both single mutants, each containing a single histidine residue. Both mutants are completely inactivated by diethyl pyrocarbonate treatment; the competitive inhibitor Pi protects both mutants from inactivation. The His66/His72 double mutant was completely inactive.

Porcine liver low M(r) phosphotyrosine protein phosphatase: the amino acid sequence

Porcine low M(r) phosphotyrosine protein phosphatase has been purified and the complete amino acid sequence has been determined. Both enzymic and chemical cleavages are used to obtain protein fragments. FAB mass spectrometry and enzymic subdigestion followed by Edman degradation have been used to determine the structure of the NH2-terminal acylated tryptic peptide. The enzyme consists of 157 amino acid residues, is acetylated at the NH2-terminus, and has arginine as COOH-terminal residue. It shows kinetic parameters very similar to other known low M(r) PTPases. This PTPase is strongly inhibited by pyridoxal 5'-phosphate (Ki = 21 microM) like the low M(r) PTPases from bovine liver, rat liver (AcP2 isoenzyme), and human erythrocyte (Bslow isoenzyme). The comparison of the 40-73 sequence with the corresponding sequence of other low M(r) PTPases from different sources demonstrates that this isoform is highly homologous to the isoforms mentioned above, and shows a lower homology degree with respect to rat AcP1 and human Bfast isoforms. A classification of low M(r) PTPase isoforms based on the type-specific sequence and on the sensitivity to pyridoxal 5'-phosphate inhibition has been proposed.

The role of Cys12, Cys17 and Arg18 in the catalytic mechanism of low-M(r) cytosolic phosphotyrosine protein phosphatase

Low-M(r) phosphotyrosine protein phosphatase (PTPase), previously known as low-M(r) acid phosphatase, catalyzes the in-vitro hydrolysis of tyrosine phosphorylated proteins, low-M(r) aryl phosphates and natural and synthetic acyl phosphates. Its activity on Ser/Thr-phosphorylated proteins and on most alkyl phosphates is very poor. In this study the mechanism of benzoyl-phosphate hydrolysis was studied by means of non-mutated and mutated PTPase fusion proteins. The mechanism of benzoyl-phosphate hydrolysis catalyzed by the enzyme was compared to the known mechanism of p-nitrophenyl-phosphate hydrolysis. The results demonstrated that both hydrolytic processes proceed through common enzyme-catalyzed mechanisms. Nevertheless, the performed phosphoenzyme-trapping experiments enable us to identify Cys12 as the active-site residue that performs the nucleophilic attack at the phosphorus atom of the substrate to produce a phosphoenzyme covalent intermediate. In addition, while the role of Cys17 in the substrate binding was confirmed, its participation a second time in the step that involves the Cys12 dephosphorylation was suggested by the results of phosphoenzyme-trapping experiments. The participation of Arg18 in the substrate-binding site was demonstrated by site-directed mutagenesis that produced the conservative Lys18 and the non-conservative Met18 mutants. Both these mutants were almost inactive and not able to bind the substrate and a competitive inhibitor. Furthermore, phosphoenzyme-trapping experiments clearly excluded that Cys62 and Cys145 (that were indicated by another laboratory to be involved in the active site of the enzyme as powerful nucleophilic agents) are the residues directly involved in the formation of the phosphoenzyme covalent intermediate.

Reduction of low-molecular-weight acid phosphatase activity in Alzheimer brains

Recent studies in Alzheimer brains have shown aberrant protein phosphorylation, suggesting an alteration in protein kinases and/or phosphoprotein phosphatases. In the present study, the activity of acid phosphatase was investigated in samples prepared from postmortem normal human and Alzheimer brains. p-Nitrophenyl phosphate, a nonprotein phosphoester, was used as a substrate for acid phosphatase. The separation profile on Sephadex G-100 gel filtration chromatography revealed that two major forms of high-molecular-weight and low-molecular-weight acid phosphatase were present in the crude extracts of both rat and human brains. Another class of zinc ion (Zn2+)-dependent acid p-nitrophenyl phosphatase was also detected in rat and human brains. In Alzheimer brains, the low-molecular-weight acid phosphatase activity was significantly decreased compared to that in control brains; however, the high-molecular-weight and Zn(2+)-dependent acid phosphatase activity in control and Alzheimer brains was not different. These results suggest that reduced activity of the low-molecular-weight acid phosphatase, which possesses phosphotyrosine protein phosphatase activity, might be linked to aberrant protein tyrosine phosphorylation found in Alzheimer brains.

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.

The role of Cys-17 in the pyridoxal 5'-phosphate inhibition of the bovine liver low M(r) phosphotyrosine protein phosphatase

Mammalian tissues contain two low M(r) phosphotyrosine protein phosphatase isoforms (type-1 and type-2) that differ in the 40-73 amino-acid sequence. Only one isoform (type-2) is strongly inhibited by pyridoxal 5'-phosphate, whereas the other is poorly inhibited by this compound. The mechanism of pyridoxal 5'-phosphate inhibition of the bovine liver enzyme (a type-2 isoform) has been studied by kinetic methods using a series of pyridoxal 5'-phosphate analogues. These studies indicate that pyridoxal 5'-phosphate interacts with the enzyme in both the phosphate and aldehyde groups. Active site-directed mutagenesis has been used to investigate the sites of pyridoxal 5'-phosphate binding. Our results indicate that Cys-17, essential for enzyme activity, interacts with the phosphate moiety of pyridoxal 5'-phosphate. On the other hand, Cys-12, which is also involved in the catalytic mechanism, does not participate in pyridoxal 5'-phosphate binding.

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.