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The solution structure and thermal stability of human prostatic acid phosphatase (hPAP) in the absence and in the presence of tartaric acid were studied by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The temperature dependence of the infrared spectrum and DSC scans indicate that hPAP undergoes thermal unfolding at a temperature between 49.5 and 52.5 degrees C. Binding of tartaric acid does not lead to major changes in the secondary structure of hPAP, however, hPAP with bound tartaric acid shows a significantly increased thermal stability. These results helped to better understand the mechanism of hPAP unfolding at the elevated temperature.

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BACKGROUND: Prostatic acid phosphatase (hPAP) is a major product of the human prostate gland, yet its physiological substrate remains unknown. METHODS: Human PAP, purified from semen, was crystallized using polyethylene glycol as the precipitant and its crystal structure was determined using X-ray diffraction. The structure was refined at 3.1 A resolution to R = 16% and R(free) = 27%. RESULTS: The structure of hPAP is similar to that of other known histidine phosphatases, and the positions of its catalytic residues are conserved. N-linked carbohydrates are present at each of the possible glycosylation sites. It appears that high-mannose chains are attached to Asn 62 and Asp 301, while complex chains are at Asn 188. CONCLUSIONS: The similarity of the three-dimensional structures of rat PAP and human PAP indicates that the mechanistic analyses of the catalytic mechanism proposed for the rat enzyme should be extended to the human enzyme without reservations. The crystallographic data allowed the correlation of attachment sites of N-linked carbohydrate chains with a given carbohydrate type. The carbohydrates of the protein produced in the prostate cells and in the baculovirus expression system appear to differ at the site of complex carbohydrates attachment.

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The crystal structure of the complex between rat-prostatic acid phosphatase (PAP) and L-(+)-tartrate (Lindqvist et al., J. Biol. Chem., 1993, 268, 20744-20746) contains the model of the ligand with incorrect chirality. We report here the correct model and discuss the relation between this model and the model of the inhibitory complexes between PAP and oxy-anions.

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The effect of 5alpha-dihydrotestosterone (DHT) on the level of human prostatic acid phosphatase (hPAP) mRNA was studied using tissue slices from various benign prostatic hyperplastic glands. The absence of DHT in the incubation medium led to a gradual, significant decrease of the hPAP mRNA level. Addition of the hormone induced hPAP mRNA in a time- and dose-dependent manner. The maximal 2-4-fold induction by 10(-9) M DHT was observed after 3-5 h of incubation, and then the hPAP mRNA level was 6-20-fold higher than that in a parallel sample incubated without DHT. The results suggest that DHT is necessary to sustain the expression of hPAP in hyperplastic prostates.

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Human prostatic acid phosphatase (hPAP) [EC 3.1.3.2], a homodimer of ca. 50 kDa subunit molecular weight, shows reversible denaturation in 6 M urea at pH 2.5. Rapid dilution of the denatured enzyme allowed partial renaturation of hPAP, as measured by enzyme activity, to a level which depended on the composition of the dilution solution employed and time of the reaction. The renaturation reaction of hPAP was examined using spectral analysis (circular dichroism and fluorometry), fast size-exclusion chromatography and proteolysis by trypsin. The observed results are in agreement with the concentration-dependent kinetics of hPAP reactivation, assuming that the reconstitution of the active enzyme requires the association of subunits in dimeric form. Moreover, it suggests formation of an inactive intermediate during refolding of the denatured PAP. A mechanism of renaturation of the active enzyme from denatured PAP is proposed.

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Human prostatic acid phosphatase (EC 3.1.3.2) is a non-specific phosphomonoesterase, synthetized and secreted into seminal plasma under androgenic control. The enzyme is a dimer of molecular weight around 100 kDa. Gene coding this protein is localized on chromosome 3. Since many years prostatic phosphatase has been used as a marker of diagnosis and therapy control of cancer of the prostate gland. The biological role of this enzyme, however, remains unknown and needs further exploration.

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Human prostatic acid phosphatase (EC 3.1.3.2) was denatured in 6 M urea at pH 2.5, but was refolded by dilution at pH 7.0, as demonstrated by the recovery of nearly complete enzyme activity and dimeric structure. The conformational changes among the native, denatured and refolded states were monitored by means of steady-state and nanosecond pulse fluorometry of tryptophan residues of the enzyme. The relative quantum yield of the fluorescence was highest in the native enzyme and lowest in the denatured one, and was intermediate in the refolded enzyme, although the emission peak was reproducible after refolding. The observed decay curves of tryptophan fluorescence of the native, denatured and refolded states were analyzed by decay functions of three lifetimes. The fluorescence lifetimes of the refolded enzyme were shorter than those of the native one. The fluorescence of the denatured enzyme decayed much faster than that of the other forms. The fluorescence excitation spectra revealed that the excitation energy of phenylalanine was transferred to tryptophan(s) in the native and refolded forms, but not in the denatured form. The efficiency of the energy transfer was higher in the native enzyme than in the refolded one. It was found by excitation polarization spectra that the freedom of internal motion of tryptophans was greater in the refolded enzyme than in the native enzyme. In the denatured enzyme the polarization anisotropies were very low. These results indicate that the higher structure with respect to tryptophans of the refolded enzyme is delicately but definitely different from that of the native enzyme and that local conformation of the active center is recovered upon refolding.

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Human prostatic acid phosphatase (PAP) (EC 3.1.3.2) was covalently linked to chondroitin sulfate A from whale cartilage. In order to bind the protein amino groups with the preactivated carboxyl groups of chondroitin sulfate, 1-ethyl-3-(3'-dimethylaminepropyl)carbodiimide and N-hydroxysulfosuccinimide were used as coupling agents. The product was soluble and enzymatically active. The activity was on average 25% higher than that of the free enzyme. The product was heterogeneous in respect to charge and Mr (50-1500) kDa, as determined by chromatography on Sephacryl S 300 and polyacrylamide gel electrophoresis. The resulting polymers contained covalently bound chondroitin sulfate, as shown by the biotin-avidin test. The modified enzyme is more resistant against various denaturing agents, e.g., urea, ethanol, and heat. Thus covalent modification of PAP by cross-linking to chondroitin sulfate could be the preferred method for stabilization of its biological activity.

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Prostatic acid phosphatase [E.C. 3.1.3.2.] is a dimeric protein consisting of two identical subunits. This enzyme was denatured in 6 M urea solution at pH 2.5, and kinetical analysis of reactivation by dilution was performed. At low protein concentrations a second-order kinetics for reactivation of phosphatase, with rate constant 8.3 m M-1sec-1, was observed. At higher protein concentrations the reactivation obeyed first-order kinetics. These results seem to exclude the possibility that subunits of the prostatic phosphatase are catalytically active and suggest that the association of two monomers is necessary for full activity.

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Monoclonal antibody to purified prostatic acid phosphatase from seminal plasma was produced by fusion of spleen cells from immunized mice with the Sp2/O-Ag 14 cell line. This hybridoma-derived antibody, designated MAb-14, was classified as IgG1 immunoglobulin. The apparent affinity constant of phosphatase.MAb-14 complex formation calculated by using the Langmuir isotherm is 2.4 x 10(-8) M. The molecular weight of the complex formed under the condition of antibody excess was found to be 350K, which suggests that 2 molecules of prostatic phosphatase bind to 1 molecule of the antibody. The MAb-14 antibody bound to phosphatase had a negligible effect on the catalytic activity of the enzyme. All isoenzymatic forms of catalytically active prostatic phosphatase, resolved by isoelectric focusing or by chromatofocusing in different pH gradients, reacted with the monoclonal antibody. Several peptides of Mr 25K to 76K and of 13K to 76K were adsorbed from the prostatic tissue extract and from seminal fluid, respectively, on an MAb-14-Sepharose column. The MAb-14 monoclonal antibody was applied to the immunohistochemical investigation of prostatic phosphatase distribution in normal human prostate gland, in nodular hyperplasia, and in adenocarcinoma of the prostate. Immunostaining was observed in prostatic secretory epithelium, within the luminal content of prostatic glands, and in the neighborhood of prostatic cancer cells. Metastatic prostatic carcinoma was also strongly immunoreactive with the antibody. There was no cross-reactivity with leukocytes, kidney, liver, pancreas, spleen, breast, stomach mucosal, and colon tissues.

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Prostatic acid phosphatase (EC 3.1.3.2) was fragmented by trypsin and papain in the presence of sodium dodecyl sulphate. Trypsin-catalysed cleavage gave a peptide of 33 kDa which was subsequently trimmed to 18 kDa, 15 kDa and 13 kDa peptides. Even the small tryptic fragments reacted with antiphosphatase antibodies from rabbit serum and with monoclonal antibody mAb-14. Papain treatment under these conditions resulted in the release of a 40 kDa peptide which was gradually reduced to a 18 kDa peptide. The monoclonal antibody mAb-14 to the prostatic phosphatase was bound exclusively to the 50 kDa subunit of the phosphatase and to the 40 kDa peptide. The results suggest that the monoclonal antibody mAb-14 binding site represents a "local" sequence rather than a "conformational" one and does not require an extensive tertiary folding of the antigen molecule.

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1. Modification of dimeric human prostate acid phosphatase (EC 3.1.3.2) by diimidoesters leads to the formation of water-soluble preparations of high enzymatic activity, resistant to denaturing agents. 2. Monomeric, dimeric, trimeric and tetrameric species were found in SDS-polyacrylamide gel electrophoresis of the phosphatase cross-linked with dimethyl-suberimidate, and dimeric, trimeric and tetrameric enzymatically active species on thin-layer Sephadex 200 gel filtration. This molecular pattern evidenced formation of the inter-subunit covalent linkages. All molecular forms are immunoreactive against the polyclonal rabbit anti-phosphatase antibodies. 3. The catalytic properties of the modified phosphatase are almost the same as those of the native enzyme. Differences in the optical properties between the modified and the native enzymes point to slight conformational transitions in the modified enzyme.

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IgG1 monoclonal antibody to purified seminal fluid phosphatase was raised by fusion of spleen cells from immunized mice with cell line Sp2/O-Ag 14 using simple method of screening for antiphosphatase antibody secreting clones. All molecular forms of catalytically active seminal fluid phosphatase and prostatic tissue phosphatase, resolved by chromatofocusing in pH gradient, react with this monoclonal antibody and with rabbit antiserum to purified seminal fluid phosphatase. Peptides of Mr 25,000 to 76,000 and of Mr 13,000 to 76,000 were adsorbed from the prostatic tissue extract and from seminal plasma on the monoclonal antibody-Sepharose column.

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A new spectrophotometric method for following dephosphorylation of phosphotyrosine has been described. The absorption spectra of phosphotyrosine and tyrosine were plotted over the pH range from 3 to 9. The change in absorbance accompanying the conversion of phosphotyrosine to tyrosine was the greatest at 286 nm. The difference absorption coefficients were calculated for several pH values. Dephosphorylation of phosphotyrosine by acid phosphatases from human prostate gland, from wheat germ and potatoes obeys the Michaelis-Menten equation, whereas alkaline phosphatases calf intestine and E. coli are inhibited by excess of substrate.

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