Characterization of sheep lacrimal-gland peroxidase and its major physiological electron donor

A soluble sheep lacrimal-gland peroxidase was purified to apparent homogeneity. It had a native molecular mass of 75 kDa with a subunit molecular mass of 82 kDa and an isoelectric point of 6.5. Western blotting showed that it shares some of the enzyme antigenic determinants in common with other soluble peroxidases. The enzyme exhibits a Soret peak at 410 nm which is shifted to 431 nm by 5 equiv. of H2O2 due to the formation of compound II. The latter is, however, unstable and gradually returns to the native state. The enzyme forms complexes with CN- and N3- and is reduced by dithionite showing a characteristic reduced peroxidase spectrum. Although the enzyme oxidizes I-, SCN- and Br- optimally at pH 5.5., 5.25 and 5.0 respectively, at physiological pH, it oxidizes I- and SCN- only. Since extracellular SCN- concentration is much higher than I-, SCN- may act as the major electron donor to the enzyme. The second-order rate constants for the reaction of the enzyme with H2O2 (k+1) and of compound I with SCN- (k+2) were 4 X 10(7) M-1 X s-1 and 8.1 X 10(5) M-1 X s-1 respectively. A plot of log Vmax against pH yields a sigmoidal curve consistent with a single ionizable group on the enzyme with a pK(a) value of 5.75, controlling thiocyanate oxidation. In a coupled system with the peroxidase, H2O2, SCN-, GSH, NADPH and glutathione reductase, peroxidase-catalysed SCN- oxidation by H2O2 could be coupled to NADPH consumption. The system is proposed to operate in vivo for the efficient elimination of endogenous H2O2.

The requirement of reductant for in vitro biosynthesis of the iron-molybdenum cofactor of nitrogenase

A source of reductant is routinely added to the in vitro iron-molybdenum cofactor (FeMo-co) synthesis assay, although a requirement for reductant has not been established. This report demonstrates that the addition of reductant to the in vitro FeMo-co synthesis system is not required when Azotobacter vinelandii cell-free extract is prepared in buffer that lacks added reductant. The addition of reductant is required, however, if the A. vinelandii cell-free extract is chemically oxidized prior to addition to the assay. These results might suggest that extracts of A. vinelandii contain a physiological source of reductant that functions in the in vitro synthesis of FeMo-co. It is possible that the proteins required for FeMo-co biosynthesis (e.g. NIFNE and dinitrogenase reductase) are at the appropriate redox state to function in the in vitro reaction in the extract that is free of added reductant but not in the chemically oxidized extract. It is also possible that dinitrogenase reductase and/or NIFNE (both Fe-S proteins required for FeMo-co synthesis) might catalyze the reductant-dependent reaction for FeMo-co synthesis. Dithionite, Ti(III) citrate, and NADH are able to serve as the source of reductant for in vitro FeMo-co biosynthesis.

Gonadal damage and effects on fertility in adult patients with haematological malignancy undergoing stem cell transplantation

Gonadal damage, often associated with irreversible failure, is an invariable effect of high-dose myeloablative chemotherapy used for allogeneic or autologous bone marrow transplantation. Although not life threatening, the psychological consequences are significant. Therefore semen cryopreservation is advisable prior to initial therapy, but oocyte storage is not yet possible and embryo cryopreservation seldom feasible. Treatment protocols should be carefully selected to maximise cure rates whilst limiting injury to the reproductive system. Involvement of a reproductive endocrinologist is thus ideal from presentation, and certainly necessary pretransplant and for long-term follow-up in order to provide the endocrine assessment, counselling and fertility management which are essential for adequate transplant care. Improvement in bone marrow transplant technology and more rigorous patient selection have resulted in a higher proportion of long-term survivors. This has increased the awareness of long-term effects, such as gonadal failure, which may become apparent several months or years after transplantation. Premature ovarian and testicular failure may be overlooked by physicians managing the life-threatening disease, but for patients, the physical, emotional, psychological and social consequences of functional castration consequent on high-dose therapy can be devastating. The pathophysiology, diagnosis and management of gonadal failure are reviewed here.

Incorporation of iron and sulfur from NifB cofactor into the iron-molybdenum cofactor of dinitrogenase

NifB-co is an iron- and sulfur-containing precursor to the iron-molybdenum cofactor (FeMo-co) of dinitrogenase. The synthesis of NifB-co requires at least the product of the nifB gene. Incorporation of 55Fe and 35S from NifB-co into FeMo-co was observed only when all components of the in vitro FeMo-co synthesis system were present. Incorporation of iron and sulfur from NifB-co into dinitrogenase was not observed in control experiments in which the apodinitrogenase (lacking FeMo-co) was initially activated with purified, unlabeled FeMo-co or in assays where NifB-co was oxygen-inactivated prior to addition to the synthesis system. These data clearly demonstrate that iron and sulfur from active NifB-co are specifically incorporated into FeMo-co of dinitrogenase and provide direct biochemical identification of an iron-sulfur precursor of FeMo-co. Under different in vitro FeMo-co synthesis conditions, iron and sulfur from NifB-co were associated with at least two other proteins (NIFNE and gamma) that are involved in the formation of active dinitrogenase. The results presented here suggest that multiple FeMo-co processing steps might occur on NIFNE and that FeMo-co synthesis is most likely completed prior to the association of FeMo-co with gamma.

Irreversible inactivation of lactoperoxidase by mercaptomethylimidazole through generation of a thiyl radical: its use as a probe to study the active site

The mechanism of suicidal inactivation of lactoperoxidase (LPO) by mercaptomethylimidazole (MMI) has been studied. Analogue studies indicate a specific requirement for the thiol group of MMI for inactivation of LPO in the presence of H2O2. MMI is oxidized via one-electron transfer by LPO compound II as demonstrated by a spectral shift from 430 to 412 nm through an isosbestic point at 421 nm. A decrease in Soret absorbance at 412 nm and the appearance of visible peaks at 592 and 636 nm are the characteristics of the inactivated enzyme. The one-electron oxidation product of MMI was identified by e.s.r. spectroscopy as the 5,5'-dimethyl-l-pyrroline N-oxide (DMPO) adduct of the sulphur-centred thiyl radical. Both inactivation and spectral change are prevented by the radical trap DMPO, suggesting involvement of the thiyl radical in inactivation. pH-dependent inactivation kinetics indicate the involvement of an ionizable group on LPO (pKa 6.1), deprotonation of which favours inactivation. The enzyme is protected by iodide and not by guaiacol, suggesting that MMI interacts at or near the iodide-binding site which is away from the aromatic-donor-binding site. The inactive enzyme can form compound II and bind aromatic donor, indicating that the MMI oxidation product does not attack haem iron or aromatic-donor-binding site. We suggest that MMI interacts at the iodide-binding site for oxidation and the reactive product, probably the thiyl radical, is incorporated into the adjacent electron-rich site of haem porphyrin to cause inactivation.

Detection of type specific human papillomavirus (HPV) DNA in cervical cancers of Indian women

Commercial Vira Pap and Vira Type kits of Life Technologies Inc., U.S.A., were used to determine prevalence and type specific distribution of human papilloma viruses (HPV) in 18 biopsy samples of cervical carcinomas and 26 specimens of exfoliated cervical cells (swabs). The women were either attending out-patient's department of a suburban hospital or a cancer hospital in Calcutta, India. HPV DNA was detected in 9 biopsy specimens but not in any of the cervical swabs. Five of the 9 HPV positive biopsies had HPV DNA type 16/18. Neither HPV 6/11 nor HPV 31/33/35 DNAs were detected in any of these 9 specimens. Results indicated possible presence of HPV DNAs of types other than the above in at least 4 specimens.

Cytokinetic studies of oral cancer cells using bromodeoxyuridine labelling in relation to factors influencing prognosis

Cytokinetics of 27 untreated oral squamous cell carcinomas were evaluated by in vitro bromodeoxyuridine (BrdU) labelling. A mononuclear cell suspension was prepared for the labelling using collagenase and DNase treatment. The labelled cells were visualised by immunofluorescence staining with an anti-BrdU monoclonal antibody. The labelling index (LI%) was calculated by determining the percentage of BrdU labelled cells. The LIs of the carcinomas ranged from 3.8 to 19.2%. The LIs of poorly-differentiated (HG3) tumours were 2-3-fold higher compared with those of well-differentiated (HG1) and moderately-differentiated (HG2) carcinomas. Results also showed statistically significant (P < 0.0005) increases in LIs from nuclear grade 1 (NG1) to nuclear grade 3 (NG3) carcinomas. Higher LIs were observed in stage III/IV (10.82 +/- 4.62; 10.36 +/- 4.90) than those in stage I (6.87 +/- 2.09) and II (7.14 +/- 1.87) carcinomas. A significant (P < 0.0005) difference in LI values was found between the patients with positive and negative lymph nodes. Good correlation (r = 0.77) was exhibited between the LI values and mitotic counts (MC) of the specimens. These results on oral cancer cell proliferation seem to have prognostic implications.

Association of p53 expression with cytokinetics and HPV capsid antigen prevalence in oral carcinomas

p53 protein expression in oral squamous cell carcinomas (SCCs) was studied in relation to presence of HPV capsid antigens and tumour cell kinetics. The protein and viral antigens were determined from 64 SCCs employing immunoperoxidase and immunofluorescence techniques, respectively. Cell kinetics were assessed by in vitro bromodeoxyuridine labelling. Different levels of p53 were detected in 61% cases. Well-differentiated SCCs (88%) showed increased p53 expression compared with the less differentiated ones. In SCCs with higher cell proliferation rate (LI%, 13.25 +/- 4.64) the expression was almost absent. However, it was higher in stage I than in stage II/III carcinomas and occurred in 54.5% and 75% cases of HPV antigen-positive and -negative (or very little) SCCs, respectively.

Partial hypopituitarism following total body irradiation in adult patients with haematological malignancy

We present the endocrine parameters of two adult patients with partial hypopituitarism documented at 6 and 8 months after chemotherapy, single fraction total body irradiation (10.5 Gy) and autologous bone marrow transplantation. The hormone profiles demonstrate severe somatotroph insufficiency and impaired adrenocorticotroph secretory capacity, despite sparing of the gonadotroph compartment. We recommend stimulatory testing of hypothalamic-pituitary function from 3 months post-transplant, as basal hormonal concentrations may be equivocal, and supplementation may significantly improve quality of life.

Differentiation induced increase of platelet-activating factor acetylhydrolase in HL-60 cells

Platelet-activating factor (PAF) acetylhydrolase catalyzes the conversion of PAF to lyso-PAF and acetate. In this study we show that induced cellular differentiation of HL-60 cells grown in chemically defined media by dimethylsulfoxide (DMSO) to granulocytic cells increases the acetylhydrolase activity with a concomitant increased secretion of the enzyme into the media. This increase in acetylhydrolase activity is blocked by the presence of actinomycin D (1 microM) or cycloheximide (1-2 microM) in the culture media. Acetylhydrolase is located both in the cytosolic and particulate fractions; the relative distribution of acetylhydrolase activity in the particulate fraction and cytosol increases and decreases respectively, as the differentiation progresses. The addition of an intracellular protein transport inhibitor, monensin, causes further accumulation of acetylhydrolase activity in the particulate fraction and a decrease in the media, with no effect on the acetylhydrolase activity in the cytosol. Acetylhydrolase in differentiated HL-60 cells acquires properties similar to those of the plasma acetylhydrolase in that it becomes less sensitive to 5,5'-dithiobis-2-nitrobenzoic acid and p-bromophenacylbromide inhibition than the acetylhydrolase in undifferentiated cells. The acetylhydrolase secreted into the media by the differentiated cells was almost totally insensitive to these inhibitors, whereas the acetylhydrolase from the particulate fraction gave an intermediate response; the cytosolic acetylhydrolase was sensitive to both inhibitors. However, the acetylhydrolase secreted by differentiated HL-60 cells has a different electrophoretic mobility, temperature sensitivity, and association with lipoproteins when compared to that of human plasma acetylhydrolase. Collectively, these results indicate cellular differentiation induces intracellular acetylhydrolase activity through a mechanism involving both transcriptional and translational events. Furthermore, the acetylhydrolase synthesized during the DMSO-induced differentiation of HL-60 cells is then secreted into the media via the intracellular membrane transport system for proteins. Based on results obtained with HL-60 cells as a cell model, it is likely that more than one isoform of acetylhydrolase exists in the extracellular milieu.

Nucleotide and divalent cation specificity of in vitro iron-molybdenum cofactor synthesis

The nucleotide and divalent cation requirements of the in vitro iron-molybdenum cofactor (FeMo-co) synthesis system have been compared with those of substrate reduction by nitrogenase. The FeMo-co synthesis system specifically requires ATP, whereas both 1,N6-etheno-ATP and 2'-deoxy-ATP function in place of ATP in substrate reduction (M. F. Weston, S. Kotake, and L. C. Davis, Arch. Biochem. Biophys. 225:809-817, 1983). Mn2+, Ca2+, and Fe2+ substitute for Mg2+ to various extents in in vitro FeMo-co synthesis, whereas Ca2+ is ineffective in substrate reduction by nitrogenase. The observed differences in the nucleotide and divalent cation specificities suggest a role(s) for the nucleotide and divalent cation in in vitro FeMo-co synthesis that is distinct from their role(s) in substrate reduction.

Prospective study of pituitary-gonadal function to evaluate short-term effects of ablative chemotherapy or total body irradiation with autologous or allogenic marrow transplantation in post-menarcheal female patients

Pituitary-gonadal (P-G) function was evaluated 0-3 months before and 3-4 months after bone marrow transplantation (BMT) in 15 post-menarcheal females aged 17-30 (21.6 +/- 0.34) years with haematological malignancies. All patients had evidence of gonadal insufficiency prior to BMT in that their basal and human menopausal gonadotrophin (HMG)-stimulated oestradiol (E2) levels were significantly lower than those of control subjects. The patients also had markedly higher basal FSH levels and exaggerated responses to 100 micrograms iv gonadotrophin release hormone bolus compared with those of control subjects. However, the conditioning regimens employed prior to BMT, i.e. cytotoxic chemotherapy (CT) and total body irradiation (TBI), acting either singly or in combination, caused further ovarian damage. As a result, their gonadotrophins rose further into the menopausal range. Their oestradiol secretion diminished and ovaries became almost unresponsive 3-4 months after BMT. Pelvic ultrasound undertaken in 5 patients before and after BMT demonstrated a reduction in ovarian size associated with follicular depletion. All patients developed menopausal symptoms and became amenorrhoeic during this period. Contrary to expectation, the hormonal changes occurring acutely were similar in patients undergoing radiation-based regimens and those conditioned with high-dose chemotherapy alone. Also, the severity of ovarian dysfunction appeared independent of age at transplantation, the nature of the conditioning-regimen or the type of transplant. Gonadotrophic, thyrotrophic, lactotrophic and adrenocorticotrophic secretions were unaffected. These data indicate that the ovary suffers an acute insult during short-term chemotherapy but the anterior pituitary gland retains its trophic hormone reserve and secretory capacity.

Germ cell failure and Leydig cell insufficiency in post-pubertal males after autologous bone marrow transplantation with BEAM for lymphoma

Thirteen post-pubertal male patients aged 17-25 years were assessed for pituitary-gonadal function 0-3 months prior to and 2-3 months post-bone marrow transplantation for haematological malignancy. All patients had multiagent cytotoxic treatment prior to transplantation and 30% were found to have germ cell dysfunction with abnormal semen parameters before high-dose therapy indicating damage to the germinal epithelium. They also had evidence of reduced Leydig cell reserve even before transplantation. During transplantation all patients sustained sustained gonadal injury, the effect on their germ cells being more pronounced than on the Leydig cells. Fifty per cent had reduction in testicular volume and all had azoospermia 2-3 months post-transplantation. Our results indicate that short-term chemoradiotherapy causes profound damage to the germ cell compartment of the testis, with less severe damage to the Leydig cells, but no overt injury to the anterior pituitary gland. The changes appeared to be identical in patients conditioned with total body irradiation-based protocols and those who received only high-dose chemotherapy prior to bone marrow transplantation.

Successful pregnancies in women following single autotransplant for acute myeloid leukemia with a chemotherapy ablation protocol

Of 30 women surviving a minimum of 18 months following treatment for AML with a high-dose chemotherapy regimen with autologous bone marrow transplantation (ABMT), 24 were premenopausal at the time of transplantation. All were given a detailed questionnaire concerning menstruation, menopausal symptoms and pregnancy; 22 responded. Of these 22, 10 had received a single transplant procedure and 12 a double transplant procedure. In the 10 recipients of a single transplant, 4 women (age range 32-50 years) developed ovarian failure and 6 (age range 21-32 years) resumed spontaneous cyclical menstruation. Five of the 6 menstruating women became pregnant between 4 and 40 months following ABMT. Three pregnancies went to term and each resulted in the delivery of a full-term apparently normal infant. Of the 12 women who received a double ABMT (age range 32-47 years), 11 developed clinical and/or biochemical evidence of ovarian failure. The median age in the latter group was 35 years, however, compared with 28 years in the single ABMT group. These data show that it is possible to give a single very high-dose course of chemotherapy in younger patients without compromising fertility.

Biosynthesis of the iron-molybdenum cofactor of nitrogenase

The iron-molybdenum cofactor (FeMo-co) of nitrogenase is a unique molybdenum-containing prosthetic group that has been proposed to form an integral part of the active site of dinitrogenase. In Klebsiella pneumoniae, at least six nif (nitrogen fixation) gene products are required for the biosynthesis of FeMo-co, including NIFB, NIFNE, NIFH, NIFQ, and NIFV. An in vitro system for the synthesis of FeMo-co, which requires MgATP, molybdate, homocitrate, and at least the products of nifN, E, B, and H, has provided an enzymatic assay for the purification of many of the gene products required for FeMo-co biosynthesis. Although the structure of the cofactor has been solved recently, much about the biosynthetic pathway remains unknown. This article reviews what is known about the various components required for FeMo-co biosynthesis.

Dinitrogenase reductase- and MgATP-dependent maturation of apodinitrogenase from Azotobacter vinelandii

The requirements for iron-molybdenum cofactor (FeMo-co) activation of apodinitrogenase from Azotobacter vinelandii strain UW97, which lacks dinitrogenase reductase activity as assayed by substrate reduction, have been examined. Activation of apodinitrogenase from strain UW97 by FeMo-co requires the addition of both dinitrogenase reductase and MgATP. When the same apodinitrogenase is pretreated with dinitrogenase reductase and MgATP and then partially purified, however, it does not require these components for activation by FeMo-co. This suggests that dinitrogenase reductase and MgATP are involved in processing apodinitrogenase to a FeMo-co activatable form. This processing step coincides with a change in the subunit composition of apodinitrogenase from alpha 2 beta 2 to a form with an additional subunit (gamma) attached. The apodinitrogenase with the associated gamma subunit is apparently the form of the protein that is competent for activation by FeMo-co.

Correlation of mitotic abnormalities and the presence of human papillomavirus antigens in squamous cell carcinomas of the oral cavity

To determine the association of human papillomavirus (HPV) with oral cancer lesions containing abnormal mitoses, we analysed 54 of them by immunohistochemical techniques for the presence of HPV structural antigens and correlated the results with their histology. Sixteen out of 19 lesions with abnormal mitotic figures (MFs) and 15 of the 25 lesions with normal MFs contained the HPV antigen. However, 9 of the 11 koilocytotic lesions with abnormal MFs and 13 of the 17 lesions with normal MFs were HPV antigen-positive. The nature of mitosis was not influenced by the grades of koilocytosis. No correlation of HPV antigen positivity and severity of the oral carcinomas was observed.