Transmission of foreshock waves through Earth's bow shock.

The Earth's magnetosphere and its bow shock, which is formed by the interaction of the supersonic solar wind with the terrestrial magnetic field, constitute a rich natural laboratory enabling in situ investigations of universal plasma processes. Under suitable interplanetary magnetic field conditions, a foreshock with intense wave activity forms upstream of the bow shock. So-called 30 s waves, named after their typical period at Earth, are the dominant wave mode in the foreshock and play an important role in modulating the shape of the shock front and affect particle reflection at the shock. These waves are also observed inside the magnetosphere and down to the Earth's surface, but how they are transmitted through the bow shock remains unknown. By combining state-of-the-art global numerical simulations and spacecraft observations, we demonstrate that the interaction of foreshock waves with the shock generates earthward-propagating, fast-mode waves, which reach the magnetosphere. These findings give crucial insight into the interaction of waves with collisionless shocks in general and their impact on the downstream medium.

Dispersive nature of high mach number collisionless plasma shocks: Poynting flux of oblique whistler waves.

Whistler wave trains are observed in the foot region of high Mach number quasiperpendicular shocks. The waves are oblique with respect to the ambient magnetic field as well as the shock normal. The Poynting flux of the waves is directed upstream in the shock normal frame starting from the ramp of the shock. This suggests that the waves are an integral part of the shock structure with the dispersive shock as the source of the waves. These observations lead to the conclusion that the shock ramp structure of supercritical high Mach number shocks is formed as a balance of dispersion and nonlinearity.

Antitumor and biological effects of black pine (pinus nigra) pollen nuclease.

The antitumor effect of black pine (Pinus nigra) pollen nuclease (PN) tested in vitro was negligible in comparison with bovine seminal ribonuclease (BS-RNase). However, in the experiments in vivo a significant decrease of the human melanoma tumor size was observed in the mice treated with this nuclease and also with the animal RNases and DNase I. In nude mice injected intratumoraly with PN (10 microg/dose) the tumor size decreased from 100% in the control mice to 46% in treated mice whereas in counterparts treated with BS-RNase and DNase I the tumor growth was reduced a little more, however after ten times higher doses (100 and 80 microg per dose). Certain aspermatogenic and embryotoxic activity as an expression of side effects of PN and comparative enzymes also appeared, but it was lower compared to the effect of bovine seminal ribonuclease. Immunogenicity of PN was significantly weaker in comparison with BS-RNase. The antibodies against black pine nuclease produced in the injected mice did not inactivate the biological effects of this plant nuclease in vivo. In conclusion PN nuclease proved in vivo higher antitumor activity against human melanoma tumors growing in athymic mice in comparison with animal bovine seminal ribonuclease and DNase I.

Growth inhibitory effect of the antibody to hematopoietic stem cell antigen CD34 in leukemic cell lines.

Growth-inhibitory and proapoptotic effects of the monoclonal antibody to CD34 molecule, clone 4H11, were tested in CD34+ leukemic cell lines (MOLM-9, JURL-MK1, HEL) and CD34- cell lines (PS-1, ML-2 and CTV-1). We have found that the monoclonal antibody to CD34 inhibited the proliferation and induced apoptosis of all CD34+ cell lines. We did not observe induction of differentiation by anti-CD34 antibody, but a growth arrest of cells in the G0/G1 phase of the cell cycle was detected in all the cell lines studied. Combinations of anti-CD34 antibody with both type I (alpha, beta) or type II (gamma) interferons did not enhance the effects on the cell growth or inhibition of cellular proliferation of the antibody alone. Our data suggest that the monoclonal antibody to CD34 molecule prepared from clone 4H11, after sufficient experimental and preclinical testing on laboratory animals, may provide a new basis for targeted antibody therapy of acute or chronic myeloid leukemia.

Mung bean sprout (Phaseolus aureus) nuclease and its biological and antitumor effects.

Bovine seminal ribonuclease (BS RNase), a dimeric homolog of bovine pancreatic ribonuclease (RNase A), is known to display special biological activities namely cytotoxicity for human tumor cells. Because some plant ribonucleases have a similar mass weight and structure as the animal ribonuclease, effects of a commercial product of Mung bean (Phaseolus aureus) nuclease (PhA) were studied on proliferation of ML-2 human tumor cells, as well as it's aspermatogenic, embryotoxic, immunogenic, and immunosuppressive activity, and therapeutic efficiency in athymic mice bearing human melanoma tumor. Concerning the antiproliferative activity, PhA nuclease was almost non-effective in vitro on ML-2 cells and also immunosuppressive activity on human lymphocyte in mixed culture was very low compared to that of BS RNase. However, significant antitumor activity was detected on human melanoma tumor after intratumoral or intraperitoneal administration into the mice. Furthermore conjugate of PhA nuclease with polyethylene glycol (PEG) injected seven times at the dose of 10 microg intraperitoneally showed identical antitumor activity as that of bovine seminal ribonuclease (BS RNase) injected by the same way at ten times higher dose. Both PhA and BS RNases exerted strong aspermatogenic effect on the width of spermatogenic layers while RNase A administration at ten times higher concentration was ineffective. PhA nuclease when compared by means of antibody cross reaction with RNase A, BS RNase and wheat leaf neutral RNase (WLN-RNase) was found to be immunologically similar to RNase A and WLN-RNase, meanwhile BS RNase showed much higher antigenicity in comparison with them.

Some biological actions of PEG-conjugated RNase A oligomers.

Previously we have shown that monomeric RNase A has no significant biological activity, whereas its oligomers (dimer to tetramer) prepared by lyophilizing from 50% acetic acid solutions, show remarkable aspermatogenic and antitumor activities. Furthermore, conjugates prepared by chemical binding of native RNase A to polyethylene glycol (PEG) have shown a significant aspermatogenic and antitumor activities. In this work we show that the chemical conjugation of PEG to the RNase A C-dimer, and to the two RNase A trimers (NC-trimer and C- trimer) decreases the aspermatogenic activity of the oligomers while increasing their inhibitory activity on the growth of the human UB900518 amelanotic melanoma transplanted in athymic nude mice. Moreover, the PEG-conjugated RNaseA oligomers are devoid, like the free oligomers, of any embryotoxic activity.

Polymer-conjugated bovine pancreatic and seminal ribonucleases inhibit growth of human tumors in nude mice.

The hydrophilic poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) was used for RNase A or BS-RNase modification to prevent their degradation in bloodstream or fast elimination. Two PHPMA chains (classic and star-like) were synthesized and their conjugates with both enzymes were tested on the CD-1 nude mice bearing various human tumors. These RNase conjugates injected intravenously or intraperitoneally into the mice bearing melanoma, neuroblastoma or ovarian tumor caused significant reduction of transplanted tumors following ten daily doses of 2.5 and/or 1 mg/kg, respectively, while free RNase A or BS-RNase injected in doses of 10 mg/kg exerted only negligible antitumor activity. Histological examination confirmed potent cytotoxic effect of RNase A conjugates in ovarian tumor. Despite the antitumor activity observed in vivo, the in vitro cytotoxic activity of RNase A conjugates was not pronounced and did not differ from that caused by the free RNase A. The in vitro experiments with 125I-labeled preparations demonstrated that polymer conjugates were internalized by tumor cells very poorly in contrast to the dose-dependent internalization of the wild enzyme preparation. Surprisingly, mice injected with EL-4 leukemic cells, which were preincubated for 4 h with BS-RNase conjugates, exerted significantly prolonged survival compared with the control non-treated mice. It may be supposed that both BS-RNase and RNase A conjugates with PHPMA act after administration in vivo by a mechanism different from that or those occurring under in vitro conditions because in vivo they exert an antitumor action, whereas in vitro, they are ineffective. The experiments proved that RNase A, when conjugated to PHPMA, produced identical aspermatogenic and antitumor effects as BS-RNase conjugated to this polymer and that this preparation may be regarded as a potential anticancer drug.

[Use of photodynamic therapy for elimination of residual leukemic cells in autologous transplants of hematopoietic progenitor cells]. / Vyuzití fotodynamické terapie k odstranování reziduálních leukemických bunek z autologních transplantátu hematopoetických progenitorových bunek.

BACKGROUND: The increasing use of autologous hematopoietic cell support in various malignancies including leukemia and lymphoma currently bears the problem of tumor contamination of the graft with tumor cells which after re-infusion contribute to the disease relapses. It is therefore desirable to eradicate the cancer cell fraction of the graft without causing damage to the normal stem cell fraction. The purging processes based on photodynamic treatments appear to be perspective means for this purpose. METHODS AND RESULTS: We investigated the effects of 5-aminolevulinic acid (ALA)--based photodynamic treatment (ALA-PDT) on the proliferation of human leukemia cell lines HL60 (promyelocytic leukemia), ML2 (myelomonocytic leukemia) and HEL (erythroleukemia) by 3H-thymidine incorporation into the cell DNA, on the viability of cell lines HL60, HEL, DAUDI (B-cell leukemia) and JURKAT (T-cell lymphoma) as well as of blast cells of acute myeloid leukemia (AML) patients by flow cytometry-propidium iodide assay, and on the clonogenic activities of normal human bone marrow cells by in vitro cloning assays. Under the conditions used (treatment with 1 mM ALA for 4 h at 37 degrees C followed by exposure to blue light dose of 18 J/cm2) the number of proliferating HL60 cells was reduced by 2.4 logs, of ML2 cells by 3.2 logs and of HEL cells by 1 log. From the mononuclear cell preparations of AML patients the blast cells were substantially reduced in eight out of ten patients. The clonogenic activities of normal bone marrow progenitor cells were largely spared: 52.5 +/- 8.9% of colony-forming units--granulocytes macrophages (CFU-GM), and 48.6 +/- 9.7% burst forming units--erythrocytes (BFU-E). CONCLUSIONS: ALA-PDT appears to be usable principle for the depletion of residual leukemic cells from autologous transplants.

Poly[N-(2-hydroxypropyl)methacrylamide] conjugates of bovine pancreatic ribonuclease (RNase A) inhibit growth of human melanoma in nude mice.

Recently hydrophilic poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) was used for BS-RNase modification to prevent its degradation in bloodstream or fast elimination. Polymer-conjugated BS-RNase preparations proved to be cytotoxic after intravenous or intraperitoneal application, whereas native BS-RNase was ineffective. Here RNase A unimer was conjugated with two HPMA polymers (classic and star) and their antitumor effects both in vitro and in vivo were compared with those of BS-RNase polymers. Surprisingly, the antitumor effect of RNase A conjugates was also pronounced. The RNase A conjugates (classic and star) injected intravenously to mice bearing melanoma tumor caused a significant reduction in tumor volume following ten doses of 5 and 1 mg/kg, respectively. Despite the antitumor activity observed in vivo, the in vitro tested cytotoxic activity of RNase A did not differ from that caused by native RNase A while native BS-RNase (50 microg/ml) totally inhibited DNA synthesis in treated cells. The experiments with 125I-labeled preparations demonstrated concentration-dependent internalization of native BS-RNase by tumor cells within an hour, whereas the polymer conjugate (S-BS) was not internalized. On the contrary, the in vivo experiments showed that whereas 40% of S-BS conjugate persisted in bloodstream for 24h after administration, 98% of the native BS-RNase was already eliminated. Improved antitumor activities of PHPMA-modified RNases in vivo might be ascribed to their prolonged retention in bloodstream, better proteolytic stability and resistance to the action of the ribonuclease inhibitor.

Polymer conjugated bovine seminal ribonuclease inhibits growth of solid tumors and development of metastases in mice.

Bovine seminal ribonuclease (BS-RNase) exerts a potent cytotoxic activity when administered intratumorally (i.t.) to the nude mice bearing human tumors. The ineffective treatment with intravenous (i.v.) or intraperitoneal (i.p.) administration led us to the synthesis of polymeric conjugates with BS-RNase to prevent it from degradation in the blood vessel. Hydrophilic poly[N-(2-hydroxypropyl)methacrylamide] (PHPMA) was used for BS-RNase modification and a PHPMA-BS-RNase conjugates were prepared. Classic conjugate (P-BS) with BS-RNase bound to the polymer by its oligopeptide site chains was prepared by aminolytic reaction of the polymer precursor bearing reactive ester groups situated in the side chains of polymer, while star-like conjugate (S-BS) was synthesized by the reaction of PHPMA containing end-chain reactive group with BS-RNase in aqueous buffer solution at pH 8. In contrast to the total ineffectiveness of free BS-RNase administered i.v. at a daily dose 10 mg/kg, application of P-BS and S-BS conjugates at doses 2 mg/kg and 0.5 mg/kg caused significant inhibition of the growth of human melanoma in nude mice. On the base of these results the effect of i.v. administered S-BS on the metastatic process and the survival of C57Bl/6 inbred mice inoculated with B16 melanoma cells was investigated. Sixty per cent of mice treated with S-BS (0.5 mg/kg/day) survived 100 days without metastatic foci when the experiment terminated. The average survival time of the treated groups was 75.5 days compared to 32.7 days in the control group. BS-RNase conjugated to water soluble polymers appears to be the first BS RNase preparation which exerts anticancer and antimetastatic activity following its intravenous administration.

Bovine seminal ribonuclease induces in vitro concentration dependent apoptosis in stimulated human lymphocytes and cells from human tumor cell lines.

Bovine seminal ribonuclease (BS RNase), a dimeric homolog of bovine pancreatic ribonuclease has been proven to have important biological properties as aspermatogenic, antitumor, embryotoxic and immunosuppressive activities. Recently we published preliminary results concerning the ability of bovine seminal ribonuclease (BS RNase) to induce time dependent apoptosis in Con-A stimulated human lymphocytes and in human tumor cells based on DNA content and cell cycle analysis. In this study we bring more confirmative data concerning the concentration dependent in vitro induction of apoptosis in stimulated human lymphocytes and tumor cells of three human cell lines using the most sensitive and specific cytometric method for at present apoptosis determination the indirect TUNEL. BS RNase 50 microg/ml was proven to induce 49.7, 54 and 68.1% apoptosis in the cells of the ML-2 myeloid cell line and two neuroblastoma cell lines: NB-1 and NB-2, respectively. In Con A-stimulated human lymphocytes, BS RNase also induced apoptosis, eventhough not so pronounced as in human tumor cell lines. In all cultures the induction of apoptosis was proportional to BS RNase concentration ranging from 2-50 microg/ml and correlated with proportional decrease in 3H-thymidine incorporation into the newly synthesized DNA. Side by side with the ability of BS RNase to suppress the growth of human tumors transplanted to nude mice, these biological properties determine this enzyme as a promising agent with potential clinical application.

Structural changes to ribonuclease A and their effects on biological activity.

Bovine seminal ribonuclease (BS RNase) displays immunosuppressive and antitumor activities on mammalian cells, whereas bovine pancreatic ribonuclease (RNase A) is not cytotoxic. To learn more about the mechanism of BS RNase cytotoxicity, various mutants and hybrid proteins were prepared. A series of RNase A variants substituted with amino acid residues from BS RNase were prepared. Concerning quaternary structure, a significant impact was achieved in the variant TM (Q28L K31C S32C), which forms a dimer joined covalently by two intersubunit disulfide bonds. This variant is more efficient than RNase A but less active than BS RNase. Introduction of cationic residues at positions 55, 62, and 64 or substitution at positions 111 and 113 enhanced the immunosuppressive activity of RNase A but did not confer its antitumor activity. The substitution at positions 28, 31, 32, 55, 62, 64, 111, and 113 in variant T13 exerted the best immunosuppressive and antitumor effect observed among the round of the RNase A variants. Replacement of the active-site histidine residues H12 and H119 with asparagine led to the loss of both catalytic and biological activities. Five previously prepared hybrid enzymes (SRA 1-5), synthesized by introducing 16 amino acid residues from RNase A into BS RNase, exerted the same immunosuppressive activities as did the wild-type BS RNase. However, the substitution at positions 111, 113, and 115 in variant SRA 5 caused a marked decrease in its antitumor effect, indicating that these residues play an important role in antitumor efficiency. A different mechanism of action of RNases on tumor cells and/or on blastogenic transformed lymphocytes has been assumed.

Antitumor action of bovine seminal ribonuclease.

Unlike the bovine pancreatic ribonuclease (RNAase A), bovine seminal ribonuclease (BS RNAase) displays various biological activities including antitumor cytotoxicity. To learn more about its antitumor activity, we investigated BS RNAase effect on athymic nude mice bearing various tumors. BS RNAase (250 micrograms per mouse per day) was administered to the mice with prostate carcinoma for three weeks by three different routes (intraperitoneally--i.p., subcutaneously--s.c., and intratumorally-i.t.). Administration i.p. was ineffective, while s.c. administration reduced significantly size of tumors and i.t. administration abolished half of the tumors in treated mice. The i.t. administration of BS RNase to nude mice bearing melanoma showed even better results. Eighty % of mice were without tumors and in the other mice the tumors were significantly diminished. The best antitumor effect was obtained in case of seminoma. All mice bearing this tumor were cured after ten doses of BS RNAase.

Antitumor action of bovine seminal ribonuclease. Cytostatic effect on human melanoma and mouse seminoma.

This paper reports on the antitumor activity of BS RNase on human melanoma and mouse seminoma. Human melanoma cells established in culture were extremely susceptible to BS RNase, administered in concentrations ranging from 1-100 microg/ml. Concentrations of BS RNase over 10 microg/ml caused complete inhibition of cell growth. Bovine pancreatic ribonuclease (RNase A), a prototype of the ribonuclease superfamily, did not exert any effect under these conditions. Based on our previous results, athymic mice bearing human melanoma or mouse seminoma were treated with intratumoral administration of BS RNase (12.5 mg/kg b.w.). This dose was injected for five consecutive days excluding weekends. The intratumoral administration of BS RNase to nude mice bearing human melanoma showed a significant antitumor effect. There were no tumors seen in eighty percent of mice treated for three weeks, and tumors in the other mice diminished significantly. After some delay the tumors started to regrow. Prolonging of the treatment to five weeks had a similar effect. The effect of BS RNase on mouse seminoma was well pronounced. Five to seven doses of BS RNase were sufficient to eliminate tumors in all treated mice. However, as in the previous experiment, the growth of tumor tissue later reappeared.

Immunosuppressive activity of bovine seminal ribonuclease and its mode of action.

Two preparations of dimeric BS RNase-native and recombinant proteins caused identical immunosuppressive effects on MLC-stimulated human lymphocytes. The monomers of RNase A and BS RNase were ten times less active. The inhibitory effect on MLC-stimmulation was followed by 90% inhibition of cell-mediated lympholysis (CML) caused by BS RNase (10 micrograms/ml). This effect indicated that BS RNase suppressed the recognition phase of the cytotoxic reaction, resulting in inhibition of generation of cytotoxic effector cells. BS RNase exerted a similar effect on generation of cytotoxic LAK cells. Cytotoxic activity of LAK cells or CTLs against K562 target cells was abrogated only when BS RNase was added at the beginning of the sensitizing phase, but the cytotoxicity of effector cells in the destruction phase was not influenced. The effect of RNase A on the generation of cytotoxic cells was much less pronounced. To get more information about the site of action, the effect of BS RNase on early lymphocyte stimulation by PHA was investigated by using fluorescein cell probes. BS RNase (100 micrograms/ml) prevented a shift in fluorescein emission occurring within one hour of activation using fluorescein diacetate as a marker for changes in the cytoplasmic matrix. On the contrary, it did not block the shift in fluorescence emission when tested with diphenylhexatrien as a marker for changes in membrane fluidity. Furthermore the effect of BS RNase on expression of membrane antigens expressed on activated human lymphocytes was estimated. BS RNase significantly inhibited the expression of CD25, CD38 and CD71 antigens on PHA-, Con A- and MLC-stimulated human T and B lymphocytes. No substantial change in expression of these antigens was observed on IL-2-stimulated cells, but DNA synthesis was totally abrogated. These results indicate that the mode of action of BS RNase on activated T and B lymphocytes is based mainly on the suppressed expression of receptors for interleukin-2-alpha-chain and transferrin.

Effect of boar seminal immunosuppressive fraction on B lymphocytes and on primary antibody response.

Repeated i.p. or rectal treatment of male and female mice with an immunosuppressive component isolated from boar seminal vesicle secretion reduced responses of B lymphocytes to mitogen as evaluated by [3H]thymidine or bromo-deoxyuridine incorporation. The proliferative activity of T lymphocytes was not affected. By means of the immunofluorescence method, the seminal immunosuppressive component was detected on the membranes of B lymphocytes separated from the spleens of mice treated in vivo with immunosuppressor. An i.p. injection or rectal infusion of the immunosuppressive component also led to a suppression of primary antibody response to soluble and particulate antigens. These findings indicate that in vivo deposition of semen may compromise some aspects of the immune system and may be an important cofactor in the development of viral and bacterial infections in homosexual men.

Antitumor action of bovine seminal ribonuclease.

Unlike the bovine pancreatic ribonuclease (RNaseA), bovine seminal ribonuclease (BS RNase) displays various biological activities, including antitumor activity, immunosuppressivity, spermatogenicity and embryotoxicity. To learn more about its antitumor effect we tested BS RNase on the growth of 16 cell lines derived from patients with various hematological malignancies. The cells of lymphoid origin were generally more susceptible to BS RNase, administered in the range of concentrations from 2 to 100 micrograms/ml, than the myeloid ones. RNaseA used at the same concentrations did not exert any inhibitory effect. The inhibitory effect of BS RNase persisted in cultured cells after three times wash in complete medium and cell recultivation in fresh medium free of BS RNase. Four cell lines were very little sensitive (KG-1 and U-937) or resistant (JOK and NAMALWA) to BS RNase regardless of their origin. The in vivo antitumor effect of BS RNase was tested on human prostate carcinoma transplanted to athymic nude mice. The daily dose of BS RNase (0.25 mg/20 g) was administered for three weeks except weekends (15 doses) by three different ways (intraperitoneally-i.p., subcutaneously-s.c. and intratumorally-i.t.). Whereas i.p. administration was ineffective, s.c. administration significantly reduced size of the tumors and i.t. administration abolished half of the tumors in treated mice. The average weight of treated mice decreased during the experiment by 10-15%.

Mechanism of ribonuclease cytotoxicity.

Bovine seminal ribonuclease (BS-RNase), a dimeric homolog of bovine pancreatic ribonuclease A (RNase A), is toxic to mammalian cells. In contrast to dimeric BS-RNase, a monomeric BS-RNase and RNase A are not cytotoxic and are bound tightly by cytosolic ribonuclease inhibitor. To elucidate the mechanism of ribonuclease cytotoxicity, we constructed a series of hybrid and semisynthetic enzymes and examined their properties. In five hybrid enzymes, divergent residues in BS-RNase were replaced with the analogous residues of RNase A so as to diminish an interaction with a putative cellular receptor. In a semisynthetic enzyme, the disulfide bonds that cross-link the monomeric subunits of dimeric BS-RNase were replaced with thioether bonds, which can withstand the reducing environment of the cytosol. Each hybrid and semisynthetic enzyme had ribonucleolytic and cytotoxic activities comparable with those of wild-type BS-RNase. These results suggest that dimeric BS-RNase (pI = 10.3) enters cells by adsorptive rather than receptor-mediated endocytosis and then evades cytosolic ribonuclease inhibitor so as to degrade cellular RNA. This mechanism accounts for the need for a cytosolic ribonuclease inhibitor and for the cytotoxicity of other homologs of RNase A.

Immunosuppressive activity of angiogenin in comparison with bovine seminal ribonuclease and pancreatic ribonuclease.

Angiogenin, a member of the pancreatic-like ribonuclease family with a special biological action (RISBAses), is a basic protein that induces blood vessel formation. Another member of these special ribonucleases, bovine seminal ribonuclease (BS RNase), displays biological properties, including aspermatogenic, embryotoxic, antitumor and immunosuppressive activities. The effects of two angiogenin preparations tested on the biological activities mentioned above are reported and compared with those of BS RNase and RNase A. In contrast to RNase A, which was ineffective in all biological activities tested, angiogenin suppressed significantly the proliferation of human lymphocytes stimulated by phytohemagglutinin or concanavalin A or by allogenic human lymphocytes (mixed lymphocyte culture). However, angiogenin did not affect the growth of human tumor cell lines, development of cow and mouse embryos and spermatogenicity in mice. On the basis of these results, angiogenin is the first monomeric ribonuclease described so far that displays immunosuppressive activity similar to that of the dimeric BS RNase. The immunosuppressive activity of angiogenin might synergize with the effect on neovascularization of tumor tissues and thus contribute to the development of tumor.

Catalytic activity of bovine seminal ribonuclease is essential for its immunosuppressive and other biological activities.

Bovine seminal ribonuclease (BS-RNase) is a homologue of RNase A with special biological properties, including potent immunosuppressive activity. A mutant BS-RNase was created in which His-119, the active-site residue that acts as a general acid during catalysis, was changed to an aspartic acid. H119D BS-RNase formed a dimer with quaternary structure similar to that of the wild-type enzyme but with values of kcat. and kcat./Km for the cleavage of UpA [uridylyl(3'-->5')adenosine] that were 4 x 10(3)-fold lower. The mutant protein also demonstrated dramatically decreased immunosuppressive, anti-tumour, aspermatogenic, and embryotoxic activities. The catalytic activity of BS-RNase is therefore necessary for its special biological properties.