Biomedical subjects

A Wozniak

Publications and source records attributed to A Wozniak.

At least 19 recordsLinked to original sources

PubMed2003

A phase I clinical trial of spicamycin derivative KRN5500 (NSC 650426) using a phase I accelerated titration "2B" design.

The spicamycin derivative KRN5500 was considered as a potential anti-cancer agent based on in vitro and preclinical studies. A Phase I study involving 24 cancer patients in whom tumors were refractory to all other conventional therapies was conducted to determine the dose limiting toxicity, maximum tolerated dose, effectiveness, and pharmacokinetic parameters of this drug administered by 1-h IV infusion daily for five consecutive days every 3 weeks. Using an accelerated dose titration strategy, 8.4 mg/m2/d x 5 days was the maximum administered dose. Severe gastrointestinal and hepatic toxicities were observed at doses at or above 4.3 mg/m2/d x 5. The recommended Phase II dose i s 4.3mg/m2/d x 5. The distribution of KRN5500 followed a two-compartment model, and clearance did not decrease significantly over the dose range 0.8-8.4 mg/m2/d x 5. No significant correlation was observed between plasma levels and toxicity. No tumor responses were observed among the 14 patients evaluable for response.

Adult↗

PubMed2001

Clinical and molecular-cytogenetic studies in seven patients with ring chromosome 18.

We report the results of detailed clinical and molecular-cytogenetic studies in seven patients with ring chromosome 18. Classical cytogenetics and fluorescence in situ hybridization (FISH) analysis with the chromosome 18 painting probe identified five non-mosaic and two complex mosaic 46,XX,dup(18)(p11.2)/47,XX,dup(18)(p11.2),+r(18) and 46,XX,dup(18)(p11.32)/47,XX,dup(18)(p11.32),+r(18) cases. FISH analysis was performed for precise characterization of the chromosome 18 breakpoints using chromosome 18-specific short-arm paint, centromeric, subtelomeric, and a panel of fifteen Alu- and DOP-PCR YAC probes. The breakpoints were assessed with an average resolution of approximately 2.2 Mb. In all r(18) chromosomes, the 18q terminal deletions ranging from 18q21.2 to 18q22.3 ( approximately 35 and 9 Mb, respectively) were found, whereas only in four cases could the loss of 18p material be demonstrated. In two cases the dup(18) chromosomes were identified as inv dup(18)(qter-->p11.32::q21.3-->qter) and inv dup(18)(qter-->p11.32::p11.32-->p11.1: :q21.3-->qter)pat, with no evidence of an 18p deletion. A novel inter-intrachromatid mechanism of formation of duplications and ring chromosomes is proposed. Although the effect of "ring instability syndrome" cannot be excluded, the phenotypes of our patients with characteristic features of 18q- and 18p- syndromes are compared and correlated with the analyzed genotypes. It has been observed that a short neck with absence of cardiac anomalies may be related to the deletion of the 18p material from the r(18) chromosome.

Abnormalities, Multiple↗

PubMed2001

The neurofibromatosis type 2 gene is mutated in perineurial cell tumors: a molecular genetic study of eight cases.

Perineurial cell tumors (PNTs) are rare neoplasms derived from or showing differentiation toward specialized lining cells of the nerve sheath, the perineurial cells. In this study, we have evaluated neurofibromatosis type 2 (NF2) gene alterations in eight PNTs using archival formaldehyde-fixed, paraffin-embedded tissue. Two conventional soft-tissue PNTs from the upper back and chest wall, one retiform soft tissue variant from the scapular region, and five sclerosing PNTs from the fingers and palm were studied. All cases showed histological features of PNTs, and the neoplastic cells were positive for epithelial membrane antigen and negative for S100 protein. The coding sequences (exons 1 to 15) of the NF2 gene were polymerase chain reaction (PCR) amplified and evaluated for mutations by direct sequencing of the PCR products. Five NF2 point mutations, two in the 5'-untranslated region (UTR) and three in exons 3, 6, and 8, were identified in four of eight cases (50%) studied. Exon mutations resulted in changes of predicted amino acids sequences: Asp-->Asn at codon 83, Glu-->Asp at codon 182, and Leu-->Val at codon 241. In two cases (one with a missense mutation in codon 241), the same point mutation in the 5'-UTR at the nucleotide position 8958 was identified. A loss of heterozygosity (LOH) study was performed in three cases. LOH at the NF2 locus was found in one case with a mutation in the 5'-UTR. However, in another case with exon 8 and 5'-UTR mutations, deletion of one allele of the NF2 gene was previously documented by fluorescence in situ hybridization. The coexistence of NF2 gene mutations and LOH at the NF2 locus indicates that the NF2 tumor suppressor gene is altered in PNTs by the two-hit mechanism.

Adolescent↗

PubMed2001

Chronic oral administration of CI-994: a phase 1 study.

OBJECTIVES: CI-994 (N-acetyl dinaline, PD 123654) is a novel oral agent active in a broad variety of murine and human tumor xenografts. While cytotoxic in the Brown Norway (BN) rat leukemia model, growth inhibition in other murine and human tumor xenografts is predominantly cytostatic. Its specific mechanism of action remains unknown. Following CI-994 administration, inhibition of both histone deacetylation and cellular proliferation at the G1 to S transition phase of the cell cycle are observed. This Phase 1 study in patients with solid tumors was carried out to determine a maximum tolerated daily oral dose (MTD) for CI-994 administered on a chronic basis. METHODS: Fifty-three patients received CI-994 daily for treatment durations ranging from 2 to 10 weeks. Dosage escalation proceeded in 2 phases; an Acute Dosing Phase (n = 11) to define the MTD for CI-994 administered over 2 weeks and a Chronic Dosing Phase (n = 29) to define the MTD for daily administration for 8 weeks. Upon completion of the Chronic Dosing Phase, a third cohort of patients (n = 13) received CI-994 at the recommended Phase 2 dose and schedule with 2 additional single doses of drug administered separated by a 1-week washout to assess the effect of food on CI-994 pharmacokinetics. RESULTS: Thrombocytopenia was dose limiting at the MTD of 8 mg/m2/day for 8 weeks. Other toxicities included fatigue and gastrointestinal effects such as nausea, vomiting, diarrhea, constipation and mucositis. Pharmacokinetic studies revealed that peak plasma levels and AUC's generally increased with dose and that food intake did not affect the rate or extent of drug absorption. One patient with heavily pre-treated adenocarcinoma of the lung achieved a Partial Response (PR) lasting over 2 years and 3 additional patients achieved Stable Disease (SD), 1 each with non-small cell lung, colorectal, and renal cancer. CONCLUSIONS: The recommended Phase 2 starting dose is 8 mg/m2/day for 8 weeks repeated after a 2-week drug-free interval.

Administration, Oral↗

PubMed2001

Effect of altitude training on the peroxidation and antioxidant enzymes in sportsmen.

PURPOSE: The aim of this work was an evaluation of the influence of physical exercise in high-altitude conditions (about 2000 m above sea level) on thiobarbituric acid reactive substances (TBARS) and superoxide dismutase (SOD) and catalase (CAT) activities in 10 kayakers and 10 rowers. METHODS: During their training, the sportsmen performed different kinds of static and dynamic efforts. The blood samples were taken from the cubital vein on the control day at low altitude and at high altitude, and on the 4th, 10th, and 18th days of the training camp before and after exercise. The TBARS and lactic acid concentrations in blood plasma and SOD and CAT activities in erythrocytes were measured. RESULTS: A statistically significant increase of SOD and CAT activities in erythrocytes after exercise on the 4th, 10th, and 18th days of training was found. The TBARS concentration in erythrocytes decreased in a statistically significant way after the end of the 10th day of exercise (P < 0.01), and on 18th day it more than doubled (P < 0.001) when preexercise values were compared with postexercise values of each day. A statistically significant increase of TBARS concentration in blood plasma was observed only after the end of exercise on the 10th day-using the same comparison as above. A statistically significant increased lactic acid concentration in blood plasma was noticed both on 4th or 18th days of training. CONCLUSIONS: The results obtained show the increasing generation of oxygen-derived free radicals and the compensatory intensification of SOD and CAT activities after training in altitude (high mountain) conditions.

Adult↗

PubMed2001

Arbovirus surveillance in South Carolina, 1996-98.

Arboviruses isolated and identified from mosquitoes in South Carolina (USA) are described, including new state records for eastern equine encephalitis virus (EEE), St. Louis encephalitis virus (SLE), Flanders virus, Tensaw virus (TEN), and a variant of Jamestown Canyon virus (JC). Mosquitoes were collected at 52 locations in 30 of 46 South Carolina counties beginning in June 1996, and ending in October 1998, and tested for arboviruses. Of 1,329 mosquito pools tested by virus isolation (85,806 mosquitoes representing 34 mosquito species or complexes), 15 pools were positive. Virus isolations included EEE from 1 pool each of Anopheles crucians complex and Culex erraticus; a variant of JC from 1 pool of An. crucians complex; a California serogroup virus from 1 pool of Aedes atlanticus/tormentor; TEN from 5 pools of An. crucians complex and 1 pool each of Culex salinarius and Psorophora ciliata; Flanders virus from 1 pool of Culiseta melanura; and Potosi virus from 1 pool each of Aedes vexans, Coquillettidia perturbans, and Psorophora columbiae. Of 300 mosquito pools tested by antigen-capture assay for EEE and SLE (14,303 mosquitoes representing 16 mosquito species or complexes), 21 were positive for EEE and I was positive for SLE. Positive EEE mosquito pools by antigen-capture assay included An. crucians complex (14 pools), Anopheles punctipennis (1 pool), Anopheles quadrimaculatus (1 pool), Cq. perturbans (4 pools), and Cs. melanura (1 pool). One pool of Cx. salinarius was positive for SLE by antigen-capture assay. Arbovirus-positive mosquito pools were identified from 12 South Carolina counties, all located in the Atlantic Coastal Plain, and from 4 of 8 Carolina bays surveyed.

Aedes↗

PubMed2001

[The significance of cathepsins B and D and their inhibitors in cancer disease].

Cathepsins play an important role in the pathogenesis of the great number of cancer diseases i.e. in breast, head and neck, liver, pancreas, colon and skin cancer. Estimation of cathepsins activity referring to different kinds of cancer diseases has a significance both in diagnostics and in monitoring of their running. An essential role in cancer disease development is also reported for cathepsins B and D inhibitors. Using drugs that are able to inhibit the harmful activity of cathepsins, would give a chance to supplement an anti-cancer therapy with the new agents. In future, it could increase the efficiency of cancer treatment in a significant way.

Antineoplastic Agents↗

PubMed2000

Mutations in exons 9 and 13 of KIT gene are rare events in gastrointestinal stromal tumors. A study of 200 cases.

Gastrointestinal stromal tumors (GISTs), the most common mesenchymal tumors of the gastrointestinal tract, typically express the KIT protein. Activating mutations in the juxtamembrane domain (exon 11) of the c-kit gene have been shown in a subset of GISTs. These mutations lead into ligand-independent activation of the tyrosine kinase of c-kit, and have a transforming effect in vitro. Several groups have studied the clinical implication of the c-kit mutation status of exon 11 in GISTs and a possible relationship between c-kit mutations and malignant behavior has been established. Recently, a 1530ins6 mutation in exon 9 and missense mutations, 1945A>G in exon 13 of the c-kit gene were reported. The frequency and clinical importance of these findings are unknown. In this study we evaluated 200 GISTs for the presence of mutations in exons 9 and 13 of c-kit. Six cases revealed 1530ins6 mutation in exon 9 and two cases 1945A>G mutation in exon 13. All tumors with mutations in exon 9 and 13 lacked mutations in exon 11 of c-kit. None of the analyzed tumors had more than one type of c-kit mutation. All but one of the eight tumors with mutations in exon 9 or 13 of the c-kit gene were histologically and clinically malignant. All four of six cases with exon 9 mutation of which location of primary tumor was known, were small intestinal, suggesting that this type of mutation could preferentially occur in small intestinal tumors. Exon 9 and 13 mutations seem to be rare, and they cover only a small portion (8%) of the balance of GISTs that do not have mutations in exon 11 of c-kit. This finding indicates that other genetic alterations may activate c-kit in GISTs, or that KIT is not activated by mutations in all cases.

Adult↗

PubMed2000

Phase I pharmacokinetic study of the novel antitumor agent SR233377.

SR233377 is a novel thioxanthenone analogue that demonstrated solid tumor selectivity in vitro with activity confirmed in vivo against several murine tumors including those of colon, pancreas, and mammary origin. Its primary preclinical dose-limiting toxicities included myelosuppression and neurological toxicity. The neurological toxicity was acute and could be ameliorated in mice when the drug was administered as a 1-h infusion instead of rapid i.v. injection. As a result of its preclinical efficacy profile, SR233377 entered Phase I clinical investigation. The compound was administered i.v. over 2 h on day 1 repeated every 28 days. The starting dose was 33 mg/m2 (one-tenth the mouse LD10). Escalations continued to 445 mg/m2 (six escalations), where dose-limiting toxicity was observed. At this dose, acute ventricular arrhythmias, including one patient with torsades de pointes and transient cardiac arrest, occurred. Because this toxicity might have been related to the plasma peak, the protocol was amended to a 24-h infusion beginning at 225 mg/m2. With this dose, prolongation of the corrected QT interval (QTc) over the pretreatment levels resulted. Because prolonged QTc is a known forerunner to acute ventricular arrhythmias, clinical development of SR233377 was stopped. However, preclinical antitumor and toxicity studies with analogues are underway with hopes of identifying a new clinical candidate with similar antitumor effects that is devoid of cardiac toxic effects.

Adult↗

PubMed2000

A case with 47,XXY,del(11)(q23) karotype-coexistence of Jacobsen and Klinefelter syndromes.

A case with 47,XXY, del(11)(q23) karyotype-coexistence of Jacobsen and Klinefelter syndromes: A two-year-old dysmorphic male child was found to have 47,XXY,del(11)(q23) karyotype. Domination of the clinical features of Jacobsen syndrome was observed: mild mental retardation, trigonocephaly, ptosis, downward slanting palpebral fissures, low set ears, carp-shape mouth and micrognathia. Transient thrombocytopenia and leukopenia were also present. Over the following five years gynecomastia and eunuchoid body proportions became evident as clinical features of Klinefelter syndrome. This is the first description of the coexistence of both syndromes.

Brain↗

PubMed1999

Aromatase expression by astrocytes after brain injury: implications for local estrogen formation in brain repair.

Recent evidence indicates that 17beta-estradiol may have neuroprotective and neuroregenerative properties. Estradiol is formed locally in neural tissue from precursor androgens. The expression of aromatase, the enzyme that catalyses the conversion of androgens to estrogens, is restricted, under normal circumstances, to specific neuronal populations. These neurons are located in brain areas in which local estrogen formation may be involved in neuroendocrine control and in the modulation of reproductive or sex dimorphic behaviours. In this study the distribution of aromatase immunoreactivity has been assessed in the brain of mice and rats after a neurotoxic lesion induced by the systemic administration of kainic acid. This treatment resulted in the induction of aromatase expression by reactive glia in the hippocampus and in other brain areas that are affected by kainic acid. The reactive glia were identified as astrocytes by co-localization of aromatase with glial fibrillary acidic protein and by ultrastructural analysis. No immunoreactive astrocytes were detected in control animals. The same result, the de novo induction of aromatase expression in reactive astrocytes on the hippocampus, was observed after a penetrating brain injury. Furthermore, using a 3H2O assay, aromatase activity was found to increase significantly in the injured hippocampus. These findings indicate that although astrocytes do not normally express aromatase, the enzyme expression is induced in these glial cells by different forms of brain injury. The results suggest a role for local astroglial estrogen formation in brain repair.

Animals↗

PubMed1999

Dextran sodium sulphate-induced colitis activity varies with mouse strain but develops in lipopolysaccharide-unresponsive mice.

Bacteria and their products have been implicated in the pathogenesis of chronic Inflammatory Bowel disease. The aim of this study was to investigate the potential role of lipopolysaccharides (LPS) in the development of intestinal injury by comparing the effects of the dextran sodium sulphate (DSS)-induced model of colitis in LPS-sensitive and -insensitive mice. Experimental colitis was induced in LPS-sensitive mice (C3H/He) and their LPS-insensitive congenic strain (C3H/HeJ). Colitis was assessed clinically using a disease activity index (derived from the three main clinical signs; diarrhoea, rectal bleeding and weight loss) and by histological scoring of the diseased colon. The clinical signs and disease activity index did not differ between the LPS-sensitive and -insensitive costrains. Similarly, histological scores did not differ significantly for either C3H strain at any time point during exposure to DSS. However, there were differences in the inflammatory response when different strains were compared (C3H vs CBA): the effects of DSS in C3H mice were immediate, more severe and mainly involved the caecum and ascending colon. These findings suggest that LPS from colonic bacteria do not play a primary role in the initiation of DSS-induced colitis and demonstrate clear differences in the responsiveness of different mouse strains to DSS.

Animals↗

PubMed1999

Stability study on specimens mailed to a state laboratory and tested with the Gen-Probe PACE 2 assay for chlamydia.

BACKGROUND: Although specimen collection is acknowledged to be a critical factor in the testing of chlamydia, rarely do studies examine the effects of specimen transport on laboratory results. GOAL: To compare the results on specimens shipped in a controlled environment with duplicate specimens exposed to environmental conditions such as heat or extended time in transit. STUDY DESIGN: Duplicate specimens were collected from 1,017 women tested at South Carolina public health clinics. One specimen from each woman was shipped by courier and the other by U.S. mail. The results, swab collected first, method of transport, and temperature during shipment were compared for each set of specimens. Specimens were tested with the Gen-Probe PACE 2 test. RESULTS AND CONCLUSIONS: Mailed specimens were exposed to longer transport times and elevated temperatures; despite this, 99% of the results using courier specimens agreed with the mailed specimen results. Eighty-eight women tested positive and 891 women tested negative for chlamydia on both specimens. When the 11 specimens with discrepant results were retested by polymerase chain reaction, 10 were positive for chlamydia, with 9 concurring with the mailed specimen results. Results of specimens in this study were not adversely affected by heat and extended transit times when transported by U.S. Mail.

Adult↗

PubMed1998

Treatment with anti-granulocyte antibodies inhibits the effector phase of experimental autoimmune encephalomyelitis.

Emerging data suggest that polymorphonuclear leukocytes (PMNLs) can play an important role in Ag-dependent immune responses. Therefore, we have assessed the involvement of these cells in the development of an organ-specific autoimmune disease, experimental autoimmune encephalomyelitis (EAE), in the mouse. Depletion of peripheral blood PMNLs beginning day 8 after immunization significantly delayed and in some cases totally prevented the development of clinical EAE in mice. Depletion of PMNLs beginning 1 day before sensitization and continuing until day 7 postimmunization had no effect on the subsequent development of EAE, suggesting that depletion alters the efferent but not the afferent arm of the immune response. In vitro studies showed that lymphoid cells from mice protected from EAE by PMNL depletion beginning on day 8 postsensitization proliferated in response to specific Ag to a level equal to cells from sensitized animals treated with control serum, again indicating that treatment was not affecting the afferent limb of the immune response. Further evidence that PMNL may be necessary in initiating the pathology of EAE was seen in passive transfer experiments where PMNL-depleted recipients of MBP-specific lymphoid effector cells developed EAE much less effectively than did animals treated with control Ab. Taken together, these data indicate that PMNLs play a critical role in the effector phase of the development of the clinicopathologic expression of EAE in mice.

Animals↗

PubMed1997

Sex differences in the regulation of embryonic brain aromatase.

Oestrogen formed from androgen by aromatization plays a critical role in the sexual differentiation of the male brain and behaviour. A question which has still to be answered is what regulates the gender-specific changes in aromatase activity forming oestrogen during sensitive periods of brain growth. Using a primary cell culture technique and sexed embryos, we have shown that in the fetal mouse brain, oestrogen formation in the male is neuronal rather than glial and aromatase activity is regionally localized, being higher in the hypothalamus than in the cortex. The aromatase activity measured from cells in culture has the same enzyme binding affinity (apparent Km approximately 40 nM) as intact brain samples. Neurones developing in the embryonic male brain (embryonic day (ED) 15) contain higher aromatase activity (Vmax, 895 fmol/h/mg protein) than the female (Vmax, 604). Although a sex difference exists at early stages of embryonic development (ED 13), the embryonic aromatase system is regulated by steroids later in fetal development. The developing aromatase-containing neuroblasts probably form processes which connect to other aromatase neurones. Immunoreactive staining with an aromatase polyclonal antibody identifies an increase in numbers of aromatase-immunoreactive hypothalamic neuronal cell bodies following testosterone treatment. Testosterone treatment also causes both stimulation of neurite growth and branching as well as functional maturation of aromatase neurones. In particular, there is an increase in aromatase activity per neurone as well as a dramatic increase in the number of neurones expressing the enzyme. Both the functional and morphological changes depend on androgen receptor stimulation for several days in vitro. This conclusion is supported by colocalization studies which reveal a high number of fetal hypothalamic aromatase neurones co-expressing androgen receptor. We conclude that testosterone influences the growth of male hypothalamic neurones containing aromatase at a sensitive period of brain development. Endogenous steroid inhibitors of aromatase, probably formed within the neuroglia, also play a role in the control of oestrogen production. An endogenous 5alpha-reduced metabolite of testosterone, 5alpha-androstanedione, is almost as potent in inhibiting neuronal hypothalamic aromatase activity (Ki = 23 nM) as the synthetic non-steroidal inhibitors such as the imidazole, fadrozole, and the triazoles, arimidex and letrozole. It is clear that the oestrogen-forming capacity of the male hypothalamus has the special characteristics and plasticity of regulation which could affect brain differentiation at specific steroid-sensitive stages in ontogeny.

Animals↗

PubMed1997

Using video-oriented instructions to speed up sequence comparison.

MOTIVATION: This document presents an implementation of the well-known Smith-Waterman algorithm for comparison of proteic and nucleic sequences, using specialized video instructions. These instructions, SIMD-like in their design, make possible parallelization of the algorithm at the instruction level. RESULTS: Benchmarks on an ULTRA SPARC running at 167 MHz show a speed-up factor of two compared to the same algorithm implemented with integer instructions on the same machine. Performance reaches over 18 million matrix cells per second on a single processor, giving to our knowledge the fastest implementation of the Smith-Waterman algorithm on a workstation. The accelerated procedure was introduced in LASSAP--a LArge Scale Sequence compArison Package software developed at INRIA--which handles parallelism at higher level. On a SUN Enterprise 6000 server with 12 processors, a speed of nearly 200 million matrix cells per second has been obtained. A sequence of length 300 amino acids is scanned against SWISSPROT R33 (1,8531,385 residues) in 29 s. This procedure is not restricted to databank scanning. It applies to all cases handled by LASSAP (intra- and inter-bank comparisons, Z-score computation, etc.

Algorithms↗

PubMed1997

Isolation, genetic diversity, and geographic distribution of Bayou virus (Bunyaviridae: hantavirus).

Bayou hantavirus, previously implicated in human hantavirus pulmonary syndrome in Louisiana, was isolated from a rice rat (Oryzomys palustris) captured in Georgia. The presence of antibody among rice rats captured throughout the southeastern United States and the extent of diversity among the genetic variants of Bayou viruses suggest that the rice rat is the most likely natural reservoir of the virus and that both virus and host have probably co-evolved for some years.

Animals↗

PubMed1996

Effects of the type of divalent cation, Ca2+ or Mg2+, bound at the high-affinity site and of the ionic composition of the solution on the structure of F-actin.

F-actins containing either Ca2+ or Mg2+ at the single high-affinity site for a divalent cation differ in their dynamic properties [Carlier (1991) J. Biol. Chem. 266, 1-4]. In an attempt to obtain information on the structural basis of this difference, we probed the conformation of specific sites in the subunits of Mg- and Ca-F-actin with limited proteolysis by subtilisin and trypsin. The influence of the kind of polymerizing salt was also investigated. At high proteinase concentrations required for digestion of actin in the polymer form, subtilisin gives a complex fragmentation pattern. In addition to the earlier known cleavage between Met47 and Gly48 in the DNAse-I-binding loop, cleavage of F-actin between Ser234 and Ser235 in subdomain 4 has recently been reported [Vahdat, Miller, Phillips, Muhlrad and Reisler (1995) FEBS Lett. 365, 149-151]. Here we show that actually a larger segment, comprising residues 227-235, is removed and the bond between Leu67 and Lys68 in subdomain 2 is split in both G- and F-actin, and that the differences in the fragmentation patterns of the G- and F-forms are accounted for by the protection of the bond 47-48 in F-actin. The subtilisin and trypsin cleavage sites in segment 61-69, subtilisin sites in segment 227-235 and trypsin sites between Lys373 and Cys374 were less accessible in Mg-F-actin than in Ca-F-actin. These are intramolecular effects, as similar changes were observed on Ca2+/Mg2+ replacement in G-actin. The cation-dependent effects, in particular those on segment 61-69, were however less pronounced in F-actin than in G-actin. The results suggest that substitution of Mg2+ for Ca2+, and KCl-induced polymerization of CaATP-G-actin, bring about a similar change in the conformation of subdomain 2 of the monomer. The presence of Mg2+ at the high-affinity site also resulted in an increased protection of the bond 47-48. This latter appears to be an intermolecular effect because it is specific for F-actin. The susceptibility to subtilisin and trypsin was also strongly influenced by the kind and concentration of polymerizing salt. The digestion patterns suggest that the exposure and/or flexibility of the regions containing the cleavage sites diminish with enhancement of the ionic strength of the solution. The results are discussed in terms of the current models of F-actin.

Actins↗