A reference preparation of human prostatic acid phosphatase: purification, characterization and field trials

Purification, identification and Cryo-EM structure of prostatic acid phosphatase in human semen

Prostatic acid phosphatase (PAP) is a glycoprotein that plays a crucial role in the hydrolysis of phosphate ester present in prostatic exudates. It is a well-established indicator for prostate cancer due to its elevated serum levels in disease progression. Despite its abundance in semen, PAP's influence on male fertility has not been extensively studied. In our study, we report a significantly optimized method for purifying human endogenous PAP, achieving remarkably high efficiency and active protein recovery rate. This achievement allowed us to better analyze and understand the PAP protein. We determined the cryo-electron microscopic (Cryo-EM) structure of prostatic acid phosphatase in its physiological state for the first time. Our structural and gel filtration analysis confirmed the formation of a tight homodimer structure of human PAP. This functional homodimer displayed an elongated conformation in the cryo-EM structure compared to the previously reported crystal structure. Additionally, there was a notable 5-degree rotation in the angle between the α domain and α/β domain of each monomer. Through structural analysis, we revealed three potential glycosylation sites: Asn94, Asn220, and Asn333. These sites contained varying numbers and forms of glycosyl units, suggesting sugar moieties influence PAP function. Furthermore, we found that the active sites of PAP, His44 and Asp290, are located between the two protein domains. Overall, our study not only provide an optimized approach for PAP purification, but also offer crucial insights into its structural characteristics. These findings lay the groundwork for further investigations into the physiological function and potential therapeutic applications of this important protein.

Continuous monitoring of prostatic acid phosphatase using self-indicating substrates

BACKGROUND

The continuous measurement of acid phosphatase (EC 3.1.3.2) activity in serum represents an analytical task not yet sufficiently accomplished.

METHODS

Introducing two novel substrates-2-chloro-4-nitrophenyl phosphate (CNP-P), which was preferred, and 4-nitronaphthyl-1-phosphate (NN-P)-an alternative assay to measure enzymatic activity was developed and compared with a modification of Hillmann's method (azo coupling of released naphth-1-ol with a diazonium compound). Apart from different substrate concentrations of 2-chloro-4-nitrophenyl phosphate, 4 mmol/l, and naphthyl-1-phosphate (N-P), 8 mmol/l (with Fast Red TR, 5 mmol/l), respectively, following identical conditions were selected: Citrate, 50 mmol/l, pH 5.75; pentane-1,5-diol, 150 mmol/l; tartrate, 60 mmol/l; 37 degrees C.

RESULTS

Whereas intensity and stability of the azo dye unpredictably depend on the albumin concentration of the sample, the direct test with 2-chloro-4-nitrophenyl phosphate resisted sample interferences, showed no intrinsic hydrolysis by albumin, relied on stable reagents and proved superior in sensitivity, precision and ease of handling. In measuring prostatic phosphatase, the proposed procedure closely correlated with Hillmann's method. The preliminary 0.95-reference intervals for adults were 1.2-3.9 kU/l and 5.8-14.8 U/l for total activity, respectively.

CONCLUSIONS

The direct assay of the enzyme is suited as an economic, rapid and robust method for mechanized or manual use.

Production and certification of an enzyme reference material for adenosine deaminase 1 (BCR 647)

BACKGROUND

We describe the preparation of a lyophilised reference material containing purified human adenosine deaminase 1 and the certification of its catalytic concentration.

METHODS

The enzyme was purified from human erythrocytes.

RESULTS

The enzyme was >99% pure on polyacrylamide gel electrophoresis. Only trace amounts (<0.4%) of alanine aminotransferase, aspartate aminotransferase and L-lactate dehydrogenase were detected in the purified fraction. The purified adenosine deaminase had a molar mass of 41600 g/mol and an isoelectric pH at 4.7, 4.85 and 5.0. The material was prepared by diluting the purified adenosine deaminase in a matrix containing 50 mmol/l Tris-HCl buffer pH 7.4 and 30 g/l human serum albumin; dispensing in vials and freeze-drying. The batch was homogeneous and the predicted loss of adenosine deaminase activity per year on the basis of accelerated degradation studies was 0.006% at -20 degrees C and 0.04% at 4 degrees C. The certified value for adenosine deaminase catalytic concentration in the reconstituted reference material is (2.55+/-0.09) microkat/l when measured by the method that uses adenosine as substrate and glutamate dehydrogenase as auxiliary enzyme at 37 degrees C.

CONCLUSIONS

The material can be used to verify the comparability of results from different laboratories, for intra-laboratory quality control, or for calibration of the adenosine deaminase catalytic concentration measurements.

Preparation of enzyme calibration materials

Standardisation in clinical enzymology needs not only reference methods but also reference materials. While single-enzyme reference enzymes have been developed, a multienzyme certified reference material (MECRM) available in high amount remains to be produced. To transfer trueness from the value of the reference system to patients' results, validated enzyme calibrators (EC) are also needed. Both the MECRM and the ECs must exhibit the same catalytic properties as the corresponding enzymes in human plasma. Moreover, commutability of these materials with patients' samples must be experimentally tested for one or a set of methods defined by an analytical specificity equal to that of the reference method. Various experimental studies have shown that the commutability of an enzyme material depends on the source of enzyme and its purification process, the matrix (including cofactors, effectors, additives, stabilisers... ) and the mode of processing of the final material. To promote intermethod calibration in clinical enzymology, a collaborative programme between the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) and IFCC corporate members is in progress for the development of a MECRM containing amylase, ALT, AST, ALP, CK, GGT, LDH, and lipase and exhibiting a wide and defined commutability.

Production and certification of an enzyme reference material for creatine kinase isoenzyme 2 (CRM 608)

We describe the preparation of a lyophilized material containing purified human creatine kinase 2 (CK-MB), and the certification of its catalytic concentration. The material can be used to verify the comparability of results from different laboratories, for intra-laboratory quality control, or for calibration of the creatine kinase 2 catalytic concentration measurements. The enzyme was purified from human heart by ethanol precipitation and chromatography successively on DEAE-Sephacel and Blue-Sepharose. The purified enzyme had a specific activity of 998.4 U/mg and was > 99% pure on polyacrylamide gel electrophoresis. The material was examined for several possible contaminating enzymes, which were found to be absent. The purified creatine kinase 2 had two subunits (B and M) with molecular masses of 43,650 and 41,700 g/mol, respectively, and an isoelectric point at pH 5.8. The material was prepared by diluting the purified creatine kinase 2 in a matrix containing 25 mmol/L PIPES buffer, pH 7.2, 2 mmol/L ADP, 5 mmol/L 2-mercaptoethanol, 154 mmol/L sodium chloride and 50 g/L human serum albumin, dispensing it into vials and freeze-drying. The batch was shown to be homogeneous. The loss of enzyme activity on storage at -20 degrees C is predicted to be less than 0.18% per annum on the basis of accelerated degradation studies. The catalytic concentration of creatine kinase in samples of the reconstituted material is certified to be 67.2+/-1.8 U/L (1.12+/-0.03 microkat/L) when measured, at 30 degrees C, by the Recommended Method of the International Federation of Clinical Chemistry.

Gene transfer technologies for the production of enzyme and protein reference materials

To maintain the success of recommended methods and to allow comparison among various methods of enzyme analysis, enzyme reference materials are required, having catalytic properties as close as possible to those of the corresponding human enzymes. Though human sources are preferable, ethical reasons require the extraction and purification from animal tissues. By providing theoretically unlimited amounts of material, gene transfer technologies and mass culture can overcome the need of human or mammalian tissues. We have used these technologies to produce human gamma-glutamyltransferase (GGT) and pancreatic lipase (PL) in various types of host cells. Different strategies were tested, especially for GGT, depending on the inherent properties and requirements of the human enzyme. Expression and purification protocols were optimized, yielding good amounts of recombinant enzymes which share many physico-chemical and catalytic features with their natural counterparts. Kinetic constants and catalytic behavior were very similar, demonstrating the usefulness of these products as reference materials. We assume recombinant DNA technologies could be successfully applied to most enzymes or proteins assayed in clinical chemistry laboratories.

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.

Human prostatic acid phosphatase: selected properties and practical applications

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.