Isolation, characterization, and spontaneous interconversion of two forms of human prostatic acid phosphatase

Abstract

Starting with human prostatic acid phosphatase (HPAP) purified by affinity chromatography on Sepharose-bound N-(6-aminohexyl)tartramic acid [Van Etten, R. L. and Saini, M. S. (1978) Clin. Chem. 24, 1525], two forms of the enzyme can be separated by gradient elution DEAE-cellulose chromatography. The two enzyme forms are electrophoretically distinguishable on high pH gels. Under some conditions of storage one of these forms undergoes a conversion to the other. Both forms have identical amino acid compositions and Vmax values with typical substrates, but differences are observed in circular dichroism spectra, relative fluorescence intensities, Km values, and carbohydrate composition. It is concluded that the two forms differ only in the structure of their (nonphosphorylated) carbohydrate side chains. In view of the possible interconversion of the two forms upon storage, caution must be observed in any attempt to attach clinical significance to the relative amounts of the two forms.

Acid phosphatase in the lysosomal and microsomal fractions of human prostatic epithelium

“…It is known that the different types of acid phosphatase in prostatic epithelium consist of one protein backbone with a varying number of carbohydrate side chains, accounting for charge heterogeneity [1,2,[4][5][6][7][8][9]16,17]. More than 90% of the total activity in the tissue stemmed from the secretory form with the highest content of sialic acid residues; described as form I by McTigue and Van Etten [5].…”

“…A 1-ml suspension of a L,M or microsomal fraction was divided into two equal parts and to one part 0.5 ml of 0.1 mol/liter acetate buffer, pH 5.0, and 5 units neuraminidase were added. This mixture was incubated at room temperature for 24 h and subsequently dialysed overnight against 0.01 mol/liter acetate buffer, pH 5.0 [5]. Forty microliters of the neuraminidase-treated fractions and 20 pl of the untreated fractions were used after centrifugation for polyacrylamide gel electrophoresis.…”

“…When extracts of prostatic tissue were analyzed, the pattern consisted of more bands over a larger pH region [4]. After polyacrylamide gel electrophoresis or ion exchange chromatography of these extracts, two types of acid phosphatase could be separated [2,5]. They are distinguished from each other by their carbohydrate moiety; especially the varying content of sialic acid is for the greatest part responsible for the charge heterogeneity [2,.…”

Cytochemistry and biochemistry of acid phosphatases V: Electrophoretic studies on the heterogeneity of acid phosphatases from human prostate, seminal fluid, and leukocytes

“…The functional significance of this phenomenon is unknown. Another possibility is that both subunits are components of the prostate isoforms HPAP I and HPAP II [39] , which are identical in their protein backbone but differ in their carbohydrate moiety.…”

Purification and characterization of a new human prostatic acid phosphatase isoenzyme

“…This observation suggests that the heterogeneity of PAP is more complex than a simple difference in sialic acid composition. The involvement of phosphorylated sugars in the heterogeneity of PAP is also unlikely (McTigue & Van Etten, 1982).…”