Evidence for two forms of phospholipase A2 in human semen

Purification of a novel phospholipase A2 from bovine seminal plasma

Phospholipases A2 are enzymes believed to play important roles in numerous physiological systems including sperm cell maturation. Relatively little work has, however, been devoted to study these enzymes in seminal plasma. We therefore undertook the purification and characterization of this enzyme from bovine seminal plasma. After a 330-fold purification, an activity corresponding to a protein of 100 kDa was identified by gel filtration. SDS-polyacrylamide gel electrophoresis analysis of the purified fraction revealed the presence of a 60-kDa band that comigrated with the activity during ion-exchange and gel filtration chromatography as well as polyacrylamide gel electrophoresis. The enzyme possessed a pH optimum around pH 6.5 and was calcium-dependent. Using isoelectric focusing, its isoelectric point was determined to be 5.6 +/- 0.07. The enzymatic activity was resistant to p-bromophenacyl bromide, but was sensitive to gossypol and dithiothreitol. The enzyme was 2 orders of magnitude more active toward micelles formed with deoxycholate than with Triton X-100. Slight differences in the specificity toward head groups and/or sn-2-side chains were found in both assay systems. The enzyme was acid-labile and did not display affinity for heparin. It would therefore appear that the phospholipase A2 form isolated from bovine seminal plasma is of a novel type.

Immunohistochemical localization of phospholipase A2 in human and bovine male reproductive organs

Phospholipase A2 (PLA2) taken from human seminal plasma and purified about 1450-fold was injected into rabbits to prepare polyclonal antibodies. The antiserum produced and the IgG purified from the antiserum were used to compare the immunohistochemical localization of PLA2 in the human male reproductive system with that in the bull. In Western blot analyses, the polyclonal antibodies cross-reacted with purified PLA2s from human seminal plasma, bovine Cowper's glands and with partly purified PLA2 from bovine seminal vesicle fluid. On the other hand, purified PLA2s from Crotalus adamanteus venom, bovine pancreas or from bovine prostate were not recognized by the polyclonal antibodies. With an indirect peroxidase technique, PLA2 was localized in the epithelial cells of the human prostate and bovine seminal vesicles as well as in the fibrous connective tissue of bovine Cowper's gland. Indirect peroxidase staining also gave an immunoreaction in the enlarged acrosomes of round spermatids in the human testis. Using an indirect immunofluorescence method, ejaculated human spermatozoa revealed an immunoreaction which was not uniform, and the reaction was restricted to the middle piece and the acrosomal and postacrosomal regions. In conclusion, human seminal plasma, spermatozoa and prostate PLA2s were immunohistochemically related to those from bovine Cowper's gland, seminal vesicles and seminal fluid.

Immunohistochemical study of phospholipase A2 in bovine prostate

Approximately 1,100-fold purified phospholipase A2 (PLA2) from bovine prostate was injected into rabbit to prepare polyclonal antibodies. Antibodies produced showed specific immunoprecipitation only with the purified enzyme, as well as with homogenate of bovine prostatic tissue. By Western blot analysis or by immunodiffusion test, no cross-reactivity with PLA2 purified from human seminal plasma, bovine pancreas, Crotalus adamanteus venom, or with partially purified PLA2 from bovine seminal vesicle fluid or Cowper's glands was observed. Using the indirect peroxidase technique, PLA2 was localized in the cytoplasm of bovine prostatic epithelial cells. By immunogold microscopy, this enzyme was directly visualized inside the lysosomes, as well as in the endoplasmic reticulum of the glandular epithelial cells. Enzyme activity was localized in two principal subcellular sites: the mitochondria and lysosome-enriched fraction, and in the microsomal fraction.

Immunohistochemical localization of phospholipase A2 in the bovine seminal vesicle and on the surface of the ejaculated spermatozoa

1. Approximately 150-fold purified phospholipase A2 (PLA2) from bovine seminal vesicle fluid was injected into rabbit to prepare antibodies. 2. Produced antisera blocked PLA2 activity in bovine seminal plasma, seminal vesicles and its fluid and it gave single precipitation lines with the same samples. No cross-reactivity was detected with other reproductive tissues of bull as well as human seminal plasma. 3. Using indirect peroxidase technique PLA2 was localized in the apical part of epithelia cells of the bull seminal vesicle and also some minor immunohistochemical reactions were observed in the tubular lumen. Indirect peroxidase staining gave weak or no reaction at all to seminal vesicles of immature bulls. This suggests that the enzyme may be under hormonal control. 4. By indirect immunofluorescence method ejaculated spermatozoa of bull revealed immunoreaction which was not uniform and it was restricted to the middle piece, acrosome as well as postacrosomal region, but no specific immunostaining could be found on the surface of the epididymal spermatozoa. 5. Enzyme visualization by immunoelectron microscopic labelling showed a predominant localization in membrane particles inside the lumen of bovine seminal vesicle but some gold particles were also seen in granules, larger vacuoles and in cytoplasm of epithelia cells.

Studies on phospholipase A2 in human seminal plasma

1. Human seminal plasma and posterior lobe of prostate was found to have phospholipase A2 (PLA2) activity hydrolysing phosphatidylethanolamine with 14C-labelled linoleic and arachidonic acid. 2. A negative relationship was between sperm count and PLA2 activity in human seminal plasma. 3. The purified PLA2 from human seminal plasma showed high affinity to heparin, sensitivity toward p-bromophenacyl bromide, Pb2+, dithioerythritol and EDTA and it was activated by Ca2+ and Mn2+. 4. The purified PLA2 had alkaline pH optimum (7.5-10.0) and pI-value of 5.3. In SDS-PAGE enzyme preparation resulted in two bands with mol. wt of 14,000 and 16,000.

Separation of phospholipase A2 in the testis and cauda epididymis of the adult rat by chromatofocusing

Phospholipase A2 (PLA2) activity was measured in the reproductive organs of adult male rats. Phosphatidylethanolamine and phosphatidylcholine labelled with 14C linoleic (lino-PE, lino-PC) and arachidonic acid (ara-PE, ara-PC) at the 2-position were used as substrates. Lino-PE was hydrolysed most strongly by homogenates of the distal cauda epididymis but the testis, vas deferens and caput and corpus epididymis also contained hydrolytic activity. Ara-PC and lino-PC were hydrolysed by homogenates of the cauda epididymis and testis. No hydrolysis of ara-PE was detected using homogenates of reproductive tissues. Chromatofocusing of testis homogenate resulted in the appearance of two active forms of PLA2 with different pl-values (6.5 and 5.6) when lino-PE was used as substrate. Maximum activities of both enzymes with 1 mM Ca2+ were observed at pH 9.5. These isoenzymes have marked differences in response to Cu2+, N-ethylmaleimide and p-bromophenacyl bromide (p-BPB). Cu2+ and N-ethylmaleimide had almost no effect on PLA2 activity with a pl value of 6.5, but inhibited the other isoenzyme strongly; the latter was almost more resistant to p-bromophenacyl bromide. Both enzymes hydrolysed lino-PE most strongly. Chromatofocusing of an homogenate of cauda epididymis also revealed two isoenzymes of PLA2 with different pl-values (6.0 and 5.0). The latter form was resistant to p-bromophenacyl bromide but was more sensitive to Triton X-100 and sodium deoxycholate than was other isoenzyme. The pH optimum of the isoenzyme with a pl value of 6.0 ranged from 6.25 to 8.75 whilst the other isoenzyme was most active at pH 8.0-8.75.(ABSTRACT TRUNCATED AT 250 WORDS)

The phospholipase A2 of human spermatozoa; purification and partial sequence

In view of its proposed key role in the acrosome reaction, phospholipase A2 has been isolated and purified from human spermatozoa. Following SDS-PAGE, a single major band was obtained with an estimated molecular mass of 16.7 kDa. Sequence analysis of the N-terminal portion of the molecule revealed the identity of the first 19 amino acids to be YNYQFGLMIVITKGHFAMV. From this partial analysis it is evident that the phospholipase A2 of human spermatozoa represents a new sequence. Of interest is the location of glutamine-4, phenylalanine-5, methionine-8 and isoleucine-9; this sequence appears to be highly conserved throughout evolution.

Characterization and inhibitor sensitivity of human sperm phospholipase A2: evidence against pivotal involvement of phospholipase A2 in the acrosome reaction

The kinetic properties and inhibitor sensitivity of human sperm phospholipase A2 (PLA2; EC 3.1.1.4) were studied. Phospholipase activity was isolated from human spermatozoa by acid extraction. Hydrolysis of dipalmitoyl phosphatidylcholine was specific to the sn-2 position. Activity was sensitive to product inhibition (60% inhibition by 0.1 mM lysophosphatidylcholine). The effects of Ca2+ and sodium deoxycholate on enzyme activity were biphasic; maximal activities were observed at 0.5 mM concentration of each agent. PLA2 was stimulated (135%) by 3% dimethylsulfoxide and was inhibited by elevated ionic strength (approximately 70% inhibition with either 0.2 M NaCl or 0.2 M KCl). Two molecular forms of PLA2 were kinetically distinguishable, one with an apparent Michaelis constant and maximal reaction velocity of 3.0 microM and 0.64 mlU/mg protein and the other with respective constants of 630 microM and 32.0 mlU/mg protein. Both forms of the enzyme were Ca2+ dependent and heat stable; however, the low-Km activity was less resistant to 60 degrees C preincubation at pH 7.5 (28% inactivation of low-Km activity after 45 min, as compared to no effect on high-Km activity). Quinacrine was a noncompetitive PLA2 inhibitor with Kis for low- and high-Km activities of 0.42 mM and 0.49 mM, respectively. Trifluoperazine (calmodulin antagonist) inhibited the high-Km activity noncompetitively (Ki = 87 microM) and the low-Km activity by a mechanism consistent with the removal of a nonessential activator. Dissociation and rate constants for inactivation of low- and high-Km activities by p-bromophenacyl bromide were 0.28 mM and 0.032 min-1, and 0.73 mM and 0.066 min-1, respectively. PLA2 was inhibited by p-nitrophenyl-p'-guanidinobenzoate, at higher concentrations (10(-4)-10(-3) M) than required to inhibit trypsinlike proteinases; p-aminobenzamidine, another potent trypsin/acrosin inhibitor, stimulated (approximately 40%) PLA2 at concentrations from 2-5 mM but inhibited PLA2 (40-50%) at a concentration of 10 mM. MnCl2 (5mM) inhibited low- and high-Km PLA2 activities by 77% and 76%, respectively. Quinacrine (0.4 mM), trifluoperazine (20 microM), p-bromophenacyl bromide (20 microM), and MnCl2 (5 mM) were tested as inhibitors of the ionophore A23187-induced human acrosome reaction. Inhibition was noted only with quinacrine (32%) and MnCl2 (93%). The effect of MnCl2 was restricted to an interaction with A23187, rather than with PLA2; p-Bromophenacyl bromide inhibited (P less than 0.05) PLA2 (29%) when added to intact spermatozoa but had no effect on the acrosome reaction. PLA2 inhibition was poorly correlated with the acrosome reaction.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization and evolution of two human phospholipase A2 genes and two related genetic elements

Mammals are now known to contain at least two distinct classes of phospholipases A2, the progenitors of which can be seen in the venoms of snakes. Mammalian "Type I" PLA2, synthesized primarily by the pancreas, is also present in smaller amounts in other tissues including lung, spleen, and kidney. Recently, a mammalian "Type II" PLA2 has been sequenced, and shown to occur in platelets, synovial cells and fluid, cells of inflammatory peritoneal exudate, liver, intestine, kidney, and placenta. This form, referred to here as Type IIA PLA2, could play a key role in arachidonate release in both normal and pathologic inflammation. The genes encoding both forms have also been recently cloned. Here, the sites of synthesis and respective roles of the two known enzymes are discussed, along with an analysis of the evolutionary conservation of Type IIA PLA2 gene sequence. In addition, two related genetic elements containing sequences homologous to a portion of Type II PLA2 are described, which map to the same chromosome as the Type IIA PLA2 gene (chromosome 1). Either or both of these could also encode a portion of additional mammalian PLA2s.