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1.
J Cancer Res Clin Oncol ; 120(12): 737-42, 1994.
Article in English | MEDLINE | ID: mdl-7798300

ABSTRACT

Breast cancer tissue was examined for overexpression of HER-2/neu and p53 oncogene proteins. Samples from 105 breast cancer patients were investigated by Western-blot analysis and their relationship to other established markers and clinical outcome was examined. In 21.0% of the cases HER-2/neu was overexpressed, and in 46.7% the p53 protein level was increased. Expression of these two oncogene products was closely correlated. Overexpression of both oncogenes was associated with larger tumour size and negative hormone receptor. The percentage of HER-2/neu and p53 overexpression was higher in node-positive patients, although statistical evaluation was not significant. While overexpression of HER-2/neu as well as p53 in node-positive patients was associated insignificantly with shorter disease-free survival, a significant difference could be documented when the disease-free survival of patients with overexpression of both oncogene proteins was compared to that of patients with no overexpression.


Subject(s)
Breast Neoplasms/chemistry , Receptor, ErbB-2/analysis , Tumor Suppressor Protein p53/analysis , Breast Neoplasms/mortality , Breast Neoplasms/pathology , Disease-Free Survival , Female , Humans , Lymphatic Metastasis , Prognosis
2.
Cancer ; 73(1): 135-9, 1994 Jan 01.
Article in English | MEDLINE | ID: mdl-7903907

ABSTRACT

BACKGROUND: Increased expression of the HER-2/neu oncogene in breast cancer correlates with decreased estrogen receptor concentration and seems to be an important prognostic factor. The authors investigated whether there is a correlation between HER-2/neu expression and immunologic parameters representing tumor defense in patients with breast cancer. METHOD: A Western blot analysis was used to investigate HER-2/neu expression, whereas a chromium-release assay using the K562 cell line as target was used to measure natural killer (NK) cell activity. RESULTS: In patients with breast cancer, NK cell activity was significantly higher compared with patients with benign tumors (P = 0.006) or healthy control subjects (P = 0.002). Moreover, 23.3% of patients with breast cancer showed an overexpression of HER-2/neu protein. Within this group of patients, NK cell activity was significantly lower (45.6 +/- 16.1%) compared with the group with no HER-2/neu overexpression (57.3 +/- 11.0%). NK cell activity did not increase in patients with HER-2/neu overexpression. Thus, there was a statistically significant correlation of cytolytic effector cell function with HER-2/neu expression of the tumor (P = 0.003), and HER-2/neu overexpression correlated with a negative estrogen receptor status (P = 0.005). CONCLUSION: These data add further evidence to previous observations from the authors' laboratory that certain tumor characteristics may be associated with reactions of the host with breast cancer.


Subject(s)
Breast Neoplasms/genetics , Breast Neoplasms/pathology , Gene Expression Regulation, Neoplastic/genetics , Killer Cells, Natural/physiology , Oncogene Proteins, Viral/genetics , Oncogenes/genetics , Breast/pathology , Breast Diseases/genetics , Breast Diseases/pathology , Breast Neoplasms/blood , Case-Control Studies , Female , Humans , Oncogene Proteins, Viral/analysis , Receptor, ErbB-2 , Receptors, Estrogen/analysis , Receptors, Estrogen/genetics , Receptors, Progesterone/analysis , Receptors, Progesterone/genetics
3.
J Cancer Res Clin Oncol ; 120 Suppl: S19-22, 1994.
Article in English | MEDLINE | ID: mdl-8132697

ABSTRACT

The effects of coumarin (1,2-benzopyrone) on ras oncogene expression during the cell cycle of an MTV-EJras cell line was determined by flow cytometry. ras oncogene expression in cells was induced by dexamethasone and increased fivefold during G1/G0 phase and threefold in S phase. Dexamethasone also increased the percentage of cells in S phase from 21% to 31%, compared to phosphate-buffered-saline-treated control cells (P < 0.01). Coumarin decreased the percentage of dexamethasone-treated cells in S phase from 31% to 19%, with a concomitant increase in the percentage of cells in G1/G0 compared to control levels. Coumarin also reduced ras expression (mean fluorescence) by 40% in G1/G0 phase and 30% in S phase. We conclude that coumarin significantly reduces the cell-cycle progression of MTV-EJras cells and decreases ras expression in both G1 and S phases. These findings suggest a novel approach to the selective control of proliferation of malignant cells.


Subject(s)
Cell Cycle/drug effects , Coumarins/pharmacology , Gene Expression Regulation, Neoplastic/drug effects , Genes, ras , Animals , Cell Line , Cell Line, Transformed , Dexamethasone/pharmacology , Flow Cytometry , G1 Phase/drug effects , Rats , Resting Phase, Cell Cycle/drug effects , S Phase/drug effects
5.
Arch Gynecol Obstet ; 252(2): 99-102, 1992.
Article in English | MEDLINE | ID: mdl-1471918

ABSTRACT

The gender-specific prevalence of lymphangioleiomyomatosis (LAM) in premenopausal women suggests a hormonal etiology. Despite the antiestrogenic treatment (ovariectomy, tamoxifen) this disease is often refractory to therapy and almost inevitably leads to the patient's death. We describe a case where the antiproliferative effect of systemically applied interferon alpha 2b was successfully employed in addition to ovariectomy and the patient reached complete remission.


Subject(s)
Interferon-alpha/administration & dosage , Lymphangiomyoma/therapy , Mediastinal Neoplasms/therapy , Ovariectomy , Pelvic Neoplasms/therapy , Retroperitoneal Neoplasms/therapy , Tamoxifen/administration & dosage , Adult , Chylothorax/therapy , Combined Modality Therapy , Female , Humans , Hysterectomy , Interferon alpha-2 , Recombinant Proteins
6.
Invest New Drugs ; 8(2): 207-10, 1990 May.
Article in English | MEDLINE | ID: mdl-2384308

ABSTRACT

In a phase II study, 77 patients with metastatic breast cancer were treated with pirarubicin, 70 mg/m2 iv every 3 weeks. Most of them had received prior hormonal (n = 39) and/or chemotherapeutic drug treatment for advanced disease, including anthracycline-containing regimens in 17. After a median of 5.5 treatment cycles (range 1-14), objective tumor response was seen in 22/71 (31%) evaluable patients (4CR, 18 PR). Stable disease occurred in 34 (48%) patients, whereas the tumor progressed in 15 (21%). Significant hematologic toxicity (WHO grade III-IV) requiring interval and/or dose adjustments was observed in 41 (58%) patients. Other treatment-related side effects were generally mild, and included alopecia in 52 (73%), nausea and/or emesis in 50 (70%), and stomatitis and diarrhea in 3 patients each. There was no treatment-related death, nor was there any evidence of cardiac toxicity thus far. In summary, the early results of this trial suggest that pirarubicin is an active and rather well tolerated drug in pretreated patients with advanced breast cancer.


Subject(s)
Breast Neoplasms/drug therapy , Doxorubicin/analogs & derivatives , Adult , Aged , Alopecia/chemically induced , Doxorubicin/adverse effects , Doxorubicin/therapeutic use , Drug Evaluation , Female , Humans , Infusions, Intravenous , Leukopenia/chemically induced , Male , Menopause , Middle Aged , Nausea/chemically induced , Vomiting/chemically induced
7.
Anal Biochem ; 186(2): 243-50, 1990 May 01.
Article in English | MEDLINE | ID: mdl-2363495

ABSTRACT

An accurate capillary gas chromatographic method using different internal standards for determining free fatty acids, cholesterol, cholesteryl esters, and triacylglycerols in plasma and other biological sources is described. It is designed to give information about species composition and, consequently, more detailed information about changes in lipid metabolism of patients suffering from metabolic disorders. After plasma extraction the lipids, except phospholipids, are directly examined without any further derivatization. For free fatty acid determination the programmed temperature vaporizer (PTV) injector was heated from 40 degrees C (sample introduction) to 190 degrees C. In a second gas chromatographic run the PTV-injector system was heated from 60 degrees C (sample introduction) to 400 degrees C, enabling the determination of free cholesterol, cholesteryl esters, and triacylglycerol species, differing in the number of carbon atoms. Evaluation of the values obtained resulted in coefficients of variation (%) of 1.0-2.8, 2.0, 1.29-2.24, and 2.8, for free fatty acid standards, plasma free fatty acids, cholesterol and cholesteryl ester standards, and plasma total cholesterol, respectively. Free fatty acids, cholesterol, and cholesteryl esters were not influenced by storage of plasma at -24 degrees C up to 4 days prior to extraction. The results of the gas chromatographic method and the enzymatic methods correlated well. Determination by gas chromatography yielded higher total cholesterol and lower triacylglycerol values than those values obtained by enzymatic methods.


Subject(s)
Chromatography, Gas/methods , Lipids/blood , Adult , Cholesterol/blood , Cholesterol Esters/blood , Fatty Acids, Nonesterified/blood , Humans , Male , Multiple Myeloma/blood , Phospholipids/blood , Reference Standards , Temperature , Triglycerides/blood
8.
Onkologie ; 12(1): 27-9, 1989 Feb.
Article in English | MEDLINE | ID: mdl-2654788

ABSTRACT

Fifty-two previously untreated patients with multiple myeloma were randomized to either a combination of recombinant interferon (rIFN) alpha-2 and chemotherapy or chemotherapy alone. Patients were treated with vincristine, melphalan, cyclophosphamide and prednisolone every 4-6 weeks. In the combined treatment arm rIFN was administered concurrently with chemotherapy as well as during chemotherapy free intervals. The combined regimen effected 17/21 (80.9%) responses as compared to 19/27 (70.4%) responses in VMCP treated patients. Addition of rIFN to chemotherapy did not enhance hematologic toxicity. These findings suggest a somewhat higher rate of objective response in the VPMC + rIFN group, although a significant improvement in median survival by adding rIFN to conventional first line polychemotherapy in myeloma patients has not yet been achieved.


Subject(s)
Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Interferon Type I/administration & dosage , Interferon-alpha/administration & dosage , Multiple Myeloma/therapy , Adult , Aged , Clinical Trials as Topic , Combined Modality Therapy , Cyclophosphamide/administration & dosage , Female , Humans , Interferon alpha-2 , Male , Melphalan/administration & dosage , Middle Aged , Prednisone/administration & dosage , Prospective Studies , Random Allocation , Recombinant Proteins , Vincristine/administration & dosage
9.
Cancer Res ; 48(22): 6530-4, 1988 Nov 15.
Article in English | MEDLINE | ID: mdl-2846152

ABSTRACT

We investigated the effect of retinoic acid (RA) and herbimycin A (herb-A) on cell growth, cell differentiation, and colony formation of human neuroblastoma cell lines. The neuroblastoma line SK-N-SH expressed both neuroblast and nonneuronal phenotypes, whereas its subclone SH-SY5Y and the Kelly cell line were predominantly neuroblastic. Both herb-A and RA, given alone, moderately reduced cell growth and colony formation of the neuroblastic cell lines. Growth curve analyses with SK-N-SH suggested that herb-A greatly reduced the number of initially growing cells, whereas RA slightly enhanced initial cell growth. Morphological changes were determined with the use of rhodaminephalloidin staining of actin. Retinoic acid caused an increase in the fraction of neuroblast cell in SK-N-SH, and conversely of nonneuronal cells in SH-SY5Y and Kelly cell lines. Both drugs also caused partial differentiation towards a neuronal phenotype, and herb-A induced selective lysis of nonneuronal cells of SK-N-SH. Because of their discrepant effects, RA (10 microM) and herb-A (236 nM) were tested in combination at a concentration that had only moderate effects when given alone. The combination further reduced cell growth and colony formation and dramatically enhanced differentiation towards a neuronal morphology. The Kelly cell line with amplified N-myc genome, which correlates with clinical progression of neuroblastoma, was also sensitive to RA plus herb-A. These results recommend the combination of RA and herb-A for differentiation therapy of neuroblastoma.


Subject(s)
Anti-Bacterial Agents/pharmacology , Neuroblastoma/pathology , Neurons/drug effects , Quinones/pharmacology , Tretinoin/pharmacology , Benzoquinones , Cell Differentiation/drug effects , Drug Combinations , Humans , Lactams, Macrocyclic , Quinones/administration & dosage , Receptors, Opioid/analysis , Rifabutin/analogs & derivatives , Tretinoin/administration & dosage , Tumor Cells, Cultured , Tumor Stem Cell Assay
10.
Cancer Res ; 48(16): 4633-8, 1988 Aug 15.
Article in English | MEDLINE | ID: mdl-3135116

ABSTRACT

The expression and phosphotyrosine activity of pp60v-src were measured in the B31 avian sarcoma virus-transformed rat cell line by flow cytometry using monoclonal antibodies against pp60v-src (EB7) and phosphotyrosine (1G2). Although the immunocytochemical staining was markedly heterogeneous, binding of both antibodies was significantly greater to B31 cells than to untransformed Rat 1 cells. Binding of 1G2 to phosphotyrosine residues was specific; it was entirely inhibited by adding excess phenylphosphate but was not affected by phosphoserine or phosphothreonine. The relationship between the amount of phosphorylated tyrosine measured by our FCM technique and total cellular phosphotyrosine measured by phosphoamino acid analysis was linear in vanadate-treated BALB/c 3T3 cells. Treatment of B31 cells for 48 h with herbimycin A, a benzenoid ansamycin antibiotic, to decrease the expression and tyrosine kinase activity of pp60v-src caused reductions of 42% in anti-pp60v-src and 58% in anti-phosphotyrosine antibody immunofluorescence. DNA staining with the fluorescent dye propidium iodide showed no cell cycle specificity in the binding of either antibody. Herbimycin A also caused the transformed cell line to revert to the morphology, actin configuration, and growth behavior of untransformed cells; these changes were reversed within 12 h after removal of the drug. Flow cytometric evaluation of tyrosine kinase expression and activity was fast and easy, and the results correlated well with other measures of cell phenotype. This technique can be used to quantitate the effects of drugs on oncogenic proteins such as pp60v-src and their associated tyrosine kinase activity.


Subject(s)
Flow Cytometry , Protein-Tyrosine Kinases/analysis , Retroviridae Proteins/analysis , Actins/analysis , Amino Acids/analysis , Animals , Benzoquinones , Cell Line, Transformed , Cell Survival/drug effects , Lactams, Macrocyclic , Oncogene Protein pp60(v-src) , Quinones/pharmacology , Rats , Rifabutin/analogs & derivatives , Vanadates/pharmacology
11.
Wien Klin Wochenschr ; 100(10): 331-6, 1988 May 13.
Article in English | MEDLINE | ID: mdl-3261061

ABSTRACT

Acute T-lymphocytic leukemia diagnosed in a 14-year old boy on the basis of typical cell morphology, as well as by membrane antigen analysis with monoclonal antibodies, shifted to the phenotype of an acute eosinophilic leukemia 5 months after the initiation of chemotherapy. The transformation was evident by a change in morphology of cells derived from bone marrow aspirates, by cytochemistry and by a shift in the membrane antigen pattern.


Subject(s)
Eosinophils , Leukemia, Lymphoid/genetics , Leukemia/genetics , Phenotype , Adolescent , Antigens, Surface/genetics , Antineoplastic Combined Chemotherapy Protocols/adverse effects , Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Bone Marrow/pathology , Chromosome Aberrations , Eosinophils/pathology , Humans , Leukemia/chemically induced , Leukemia, Lymphoid/drug therapy , Leukemia, Lymphoid/pathology , Male , Microscopy, Electron , Remission Induction , T-Lymphocytes/pathology
12.
Cancer Res ; 47(19): 5207-12, 1987 Oct 01.
Article in English | MEDLINE | ID: mdl-3040240

ABSTRACT

Phenotypic variability of the human neuroblastoma cell line SK-N-SH was studied with the use of three subclones that interconvert at a slower rate than the parent cell line, i.e., a neuroblast-type subclone (SH-SY5Y), a nonneuronal, strongly substrate adherent subclone (SH-EP), and an intermediate type subclone (SH-IN). Rhodamine-phalloidin staining of actin fibers revealed differences in the cytoskeleton morphology of the three subclones, while the clathrin subunit proteins (heavy and light chains), components of coated vesicles, were invariant. Dramatic differences were observed for the expression of neurotransmitter systems, i.e., the mu and delta opioid receptor, the muscarinic cholinergic receptor and its effect on phosphatidylinositol turnover, and the uptake1 transporter for catecholamines. While these systems were strongly expressed in the parent line and the neuroblast-like clones SH-SY5Y and SH-IN, they were absent or barely detectable in the nonneuronal EP clone. Furthermore, the protooncogenes N- and c-myc were only expressed in the neuroblast containing lines, consistent with their growth characteristics of fully transformed cells. The strong c-myc expression in the absence of c- or N-myc amplification in SK-N-SH, adds a new form of high protooncogene activity in neuroblastoma cell lines. The remarkable differences of neurotransmitter systems and myc expression among the various phenotypes of human neuroblastoma cells should be considered in the therapy of neuroblastoma.


Subject(s)
Neuroblastoma/analysis , Proto-Oncogenes , Receptors, Dopamine/analysis , Receptors, Muscarinic/analysis , Receptors, Opioid/analysis , Actins/analysis , Cell Line , Clathrin/analysis , Humans , Neuroblastoma/genetics , Phalloidine , Rhodamines
13.
Wien Klin Wochenschr ; 99(2): 37-49, 1987 Jan 23.
Article in German | MEDLINE | ID: mdl-3031883

ABSTRACT

Within a very short time the application of molecular biology to cancer research has resulted in an essential change and extension of our knowledge of transformation processes and tumor development. For the first time these mechanisms can be understood in a causal manner and causal cancer therapy seems to be possible in the near future. In this manuscript an attempt is made to give a brief survey of the influence of oncogenes on carcinogenesis. An account is given of the origin of viral oncogenes, viral mechanisms of cell transformation and activation of cellular oncogenes. Additionally, kinetics and targets of tumor proteins are discussed. The complexity and diversity of genetic regulation of growth and differentiation is discussed in some well known diseases such as chronic myeloid leukemia, Burkitt lymphoma, retinoblastoma and acute myeloid leukemia.


Subject(s)
Neoplasms/genetics , Oncogenes , Animals , Burkitt Lymphoma/genetics , Cell Transformation, Viral , DNA Transposable Elements , Deltaretrovirus/genetics , Gene Expression Regulation , Humans , Leukemia, Myeloid/genetics , Mutation , Neoplasm Proteins/genetics , Promoter Regions, Genetic , Protein-Tyrosine Kinases/genetics , Recombination, Genetic , Retroviridae/genetics , Tumor Virus Infections/genetics , Virus Activation , Virus Replication
14.
Eur Neurol ; 25(5): 320-6, 1986.
Article in English | MEDLINE | ID: mdl-3465536

ABSTRACT

The course of leukemic disease in a male adolescent with meningeal leukemia is described. The bone marrow aspirates showed a conversion from an acute lymphatic leukemia to an eosinophilic leukemia. Four weeks after the peripheral shift of phenotype two different cell clones were detected in one CSF smear. While under ultrahigh dose araC therapy the patient died 3 months after conversion. Possible explanation for the shift of phenotype and the peculiar leptomeningeal infiltration are discussed.


Subject(s)
Cerebrospinal Fluid/cytology , Leukemia, Lymphoid/pathology , Leukemia/pathology , Meningeal Neoplasms/pathology , Adolescent , Cell Count , Clone Cells , Eosinophils , Humans , Leukemia/cerebrospinal fluid , Leukemia, Lymphoid/cerebrospinal fluid , Male , Meningeal Neoplasms/cerebrospinal fluid , Phenotype
16.
Z Gerontol ; 18(4): 241-3, 1985.
Article in German | MEDLINE | ID: mdl-3901563

ABSTRACT

Because of the decreased dopamine concentration in the elderly brain an alteration of the dopaminergic suppression of aldosterone and prolactin incretion was postulated. In contrast, the application of the dopamine D2-antagonist metoclopramide showed no significant difference as to the blockade of this dopaminergic suppression in two groups of patients with a mean age of 40 and 80 years. Subsequently aldosterone and prolactin incretion was equally stimulated in both groups.


Subject(s)
Aging , Aldosterone/blood , Dopamine/physiology , Neural Inhibition , Prolactin/blood , Adult , Aged , Brain/physiology , Humans , Hydrocortisone/blood , Metoclopramide/pharmacology , Neural Inhibition/drug effects , Renin/blood
17.
J Cancer Res Clin Oncol ; 110(1): 65-70, 1985.
Article in English | MEDLINE | ID: mdl-2410428

ABSTRACT

Serum concentrations of acute-phase-proteins C-reactive protein (CRP), alpha 1-antitrypsin (AAT), alpha 1-acid glycoprotein (AGP) as well as levels of immunoglobulins G, A and M and of complement components C3 and C4 were evaluated in 15 patients with advanced (stages III and IV) Hodgkin's disease. Of these patients 9 suffered from B symptoms including pruritus, night sweats and fever. While all patients had highly increased concentrations of CRP and AAT and 11 patients also had elevated levels of AGP in their sera, these concentrations were significantly (P less than 0.001) reducible by the administration of chemotherapy. Patients with B symptoms also had significantly higher concentrations of CRP (P less than 0.02), AAT (P less than 0.05) and AGP (P less than 0.05) in their sera than patients without. Plasmapheresis which was performed in 3 patients did not achieve a long-lasting reduction of serum concentrations of any acute-phase-protein tested. Complement components C3 and C4 exhibited a similar behaviour as acute-phase-proteins in that they were elevated in patients with B symptoms and reducible by the administration of chemotherapy (P less than 0.001 and P less than 0.02, respectively). We conclude that serum concentrations of CRP, AAT and AGP can serve as useful markers for the assessment of tumour activity in patients with advanced Hodgkin's disease. Whereas the concentrations of immunoglobulins G and A in patients were comparable to normal controls, IgM was significantly (P less than 0.05) reduced in patients who had received chemotherapy, but not in those who were newly diagnosed and had not received any treatment. Thus, chemotherapy lowered serum concentrations of IgM without influencing levels of IgG and IgA.


Subject(s)
Blood Proteins/analysis , Hodgkin Disease/blood , Acute-Phase Proteins , Adult , Antibody Formation , C-Reactive Protein/analysis , Complement System Proteins/analysis , Female , Follow-Up Studies , Hodgkin Disease/drug therapy , Hodgkin Disease/immunology , Humans , Immunoglobulins/analysis , Male , Middle Aged , Orosomucoid/analysis , Plasmapheresis , alpha 1-Antitrypsin/analysis
19.
Neurosci Lett ; 43(2-3): 293-8, 1983 Dec 30.
Article in English | MEDLINE | ID: mdl-6324046

ABSTRACT

The extracellular K+ concentration, [K+]e, was studied in unstimulated spinal cords in situ or in isolated spinal cords of frogs. The [K+]e in the dorsal horn at a depth of 150-500 microM exceeded the [K+]e found in the submeningeal fluid, in most of the upper dorsal horn and in the ventral horn by as much as 2.0 mmol . 1(-1). A substantially higher [K+]e, by 0.5-1.0 mmol . 1(-1) was also found in the intermediate region. The blockade of synaptic activity and of spontaneous activity in isolated spinal cords superfused by Ringer solution with high Mg2+ or Mn2+ concentrations decreased [K+]e in the dorsal horn and intermediate region to about 3.0 mmol . 1(-1). Similarly, the increase of spontaneous activity evoked in the isolated cords by changing the temperature of the Ringer solution, was associated with an increase of [K+]e in the dorsal spinal horn. The data suggest that the high [K+]e in the unstimulated dorsal horn results from K+ accumulation during spontaneous activity of interneurones, and its possible physiological role is discussed.


Subject(s)
Extracellular Space/metabolism , Ganglia, Spinal/metabolism , Potassium/metabolism , Animals , Interneurons/metabolism , Ion Channels/metabolism , Membrane Potentials , Rana temporaria , Synaptic Transmission
20.
Eur J Biochem ; 119(2): 225-36, 1981 Oct.
Article in English | MEDLINE | ID: mdl-6458492

ABSTRACT

The aim of the present study was to test simple reaction sequences which describe calcium-independent plus calcium-dependent phosphorylation of sarcoplasmic reticulum transport. ATPase by orthophosphate including the function of magnesium in phosphoenzyme formation. The reaction schemes considered were based on the reaction sequence for calcium-independent phosphorylation proposed previously; namely that the transport enzyme (E) forms a ternary complex (Mg . E . Pi), by random binding of free magnesium and free orthophosphate, which is in equilibrium with the magnesium-phosphoenzyme (Mg . E-P). Phosphorylation, performed at pH 7.0 20 degrees C and a constant free orthophosphate concentration using sarcoplasmic reticulum vesicles either unloaded or loaded passively with calcium in the presence of 5 mM or 40 mM CaCl2, resulted in a gradual decrease in the apparent magnesium half-saturation constant and an increase in maximum phosphoprotein formation with increasing calcium loads. When phosphorylation of sarcoplasmic reticulum vesicles preloaded in the presence of 5 mM CaCl2 was performed at a constant free magnesium concentration, a decrease in the apparent orthophosphate half-saturation constant and an increase in maximum phosphoprotein formation was observed as compared with vesicles from which calcium inside has been removed by ionophore X-537A plus EGTA treatment; however, both parameters remained unchanged by increasing free magnesium from 20 mM to 30 mM. When phosphorylation of sarcoplasmic reticulum vesicles passively loaded with calcium in the presence of 40 mM CaCl2, at which the saturation of the low-affinity calcium binding sites of the ATPase is presumably near maximum, was performed at increasing concentrations of free orthophosphate, there was a parallel shift of phosphoprotein formation as a function of free magnesium and vice versa, with no change in the maximum phosphoenzyme formation. Comparison of the experimental data with the pattern of phosphoprotein formation predicted from model equations for various theoretical possible reaction sequences suggests that phosphoenzyme formation from orthophosphate possesses the following features. Firstly, calcium present at the inside of the sarcoplasmic reticulum membrane binds to the free enzyme and in sequential order to E . Mg . Pi or Mg . E-P or to both, but neither to E. Mg nor to E . Pi. Secondly, calcium-independent and calcium-dependent phosphoproteins are magnesium-phosphoenzymes. Calcium-dependent phosphoenzyme is a magnesium-calcium-enzyme phosphate complex with 1 magnesium, 2 calciums and 1 orthophosphate (the last covalently) bound to the enzyme [Mg . E-P . (Cai)2], and not a 'calcium-phosphoprotein' without bound magnesium.


Subject(s)
Adenosine Triphosphatases/metabolism , Calcium/pharmacology , Magnesium/pharmacology , Sarcoplasmic Reticulum/metabolism , Animals , Kinetics , Mathematics , Models, Biological , Muscles/enzymology , Phosphates/pharmacology , Phosphorylation , Rabbits
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