Effect of phosphorylation on tetramerization of the tumor suppressor protein p53

Human tumor suppressor protein p53 is a 393-amino acid phosphoprotein that enhances transcription in response to DNA damage from several genes that regulate cell cycle progression. The tetrameric state of p53 is critical to wild-type function; the p53 tetramerization element is located in the C-terminal region of the protein. This region is phosphorylated at several evolutionarily conserved serines, suggesting that phosphorylation may be an important regulator of p53 function. In order to determine the effect of phosphorylation on tetramer formation, we synthesized phosphopeptides corresponding to p53(Ser303-Asp393) with phosphate incorporated at Ser315, Ser378, or Ser392, and at both Ser315 and Ser392. Equilibrium ultracentrifugation analysis showed that phosphorylation at Ser392 increased the association constant for tetramer formation nearly ten-fold. By itself, phosphorylation at Ser315 or Ser378 had little effect on tetramer formation, but Ser315 largely reversed the effect of phosphorylation at Ser392. Analysis by calorimetry suggests that phosphorylation may influence subunit affinity by an enthalpy driven process.

[Mutation of p53 gene in the transformed fibroblasts detected by nonradioisotopic single strand conformation polymorphism analysis]

The human embryonic lung fibroblasts transformation was induced by chemical mutant Glycidyl Methacrylate (GMA) in vitro. Transformed clonies were isolated and then exon 5 and exon 8 of p53 gene were specifically amplified by polymerase chain reaction. Amplified fragments were detected by using silver stained single strand conformation polymorphism analysis. The results showed that exon 8 altered in the transformed cells, indicating that p53 gene played an important role in the human embryonic lung fibroblasts transformation induced by GMA.

Hydrophobic chromatography of the HL-60 cellular fraction co-binding with hexamethylene bisacetamide

Methods of separating N-acetyl-1,6-diaminohexane (NADAH) and its immobilization to diol-silica have been developed. Hexamethylene bisacetamide (HMBA) and its metabolite NADAH are used as inducers of leukemia cell differentiation. The inducing mechanism of HMBA is still not clear. Experiments show that HMBA and NADAH undergo relatively strong hydrophobic reactions and do not readily undergo ion-exchange with the proteins of the cytosolic fraction of HL-60 cells during immobilization of NADAH; the retention time of the proteins was longer than that of the phosphatides. These results show that the adsorption of HMBA and NADAH to proteins was higher than that to phosphatides. The expected biospecific receptor binding with HMBA has not been found.

Ten kilobases of 5'-flanking region confers proper regulation of the mouse alcohol dehydrogenase-1 (Adh-1) gene in kidney and adrenal of transgenic mice

The expression profile of the mouse Adh-1 gene, which encodes class I alcohol dehydrogenase enzyme (ADH), is complex and includes tissue specificity and differential hormone responsiveness. Whereas kidney Adh-1 transcription rate is stimulated six- to sevenfold by testosterone treatment, adrenal gland ADH-1 mRNA is reduced to less than 5% of control level within 18 h following hormone administration. Androgen receptor is required for both responses since neither occurs in Tfm mutant mice lacking receptor. Hormonal and tissue-specific aspects of Adh-1 regulation were studied in transgenic mice harboring either of two constructs containing either -2.5 kb or -10 kb of 5'-flanking sequence attached to an Adh-1 minigene. The minigene transcript was expressed in kidney and adrenal tissues, but not liver, in five independent lines harboring a transgene with -2.5 kb of 5'-flanking sequence. Androgen treatment repressed the level of the minigene transcript in adrenal gland, but did not cause induction in kidney. In four lines of transgenic mice carrying the construct with -10 kb of 5'-flanking sequence, the minigene transcript was both repressed in adrenal and induced in kidney by testosterone. These lines have no detectable transgene expression in liver tissue. The -10 kb region in the mouse Adh-1 gene contains necessary controlling regions for proper tissue expression and hormonal regulation in kidney and adrenal; however, this region does not contain all essential elements necessary for expression in liver.

Activated protein C resistance in ischemic stroke not due to factor V arginine506-->glutamine mutation

BACKGROUND AND PURPOSE

Resistance to activated protein C (APC), a natural plasma anticoagulant, is the most common identifiable risk factor for venous thromboembolic disease. One point mutation in coagulation factor V that renders it APC-resistant is found in >90% of APC-resistant venous thrombosis patients. To determine the prevalence of APC resistance and of this factor V mutation in stroke, we screened a group of ischemic stroke patients.

METHODS

Hispanic ischemic stroke patients were screened using two different activated partial thromboplastin time-based assays. One assay using neat patient plasma determined APC resistance, and the other assay using patient plasma diluted into factor V-deficient plasma determined APC-resistant factor V, including the Arg506-->Gln mutation. Results were compared with those in 31 Hispanic control subjects of similar ages.

RESULTS

Six of 63 (9.5%) stroke patients had APC resistance compared with none of 31 (0%) control subjects. No patient or control subject had APC-resistant factor V, ie, the factor V Arg506-->Gln mutation.

CONCLUSIONS

In Hispanic patients with ischemic stroke, the incidence (approximately 10%) of APC resistance is not caused by the factor V Arg506-->Gln mutation. APC resistance not caused by this factor V mutation may be a risk factor for ischemic stroke in this population.

[Pharmacological action of siwei shaoyao decoction]

The Siwei Shaoyao Decoction possesses a marked effect on the alleviation of trigeminal neuralgia in rats caused by penicillin G potassium injection. As shown from the hot-plate test, it also has an obvious analgesic effect on mice. To some extent, the decoction has a significant anti-inflammatory effect on the acute edema in hind paws of rats and the effect is believed to be related to the reduction of capillary permeability.

[Chemical constituents of Gossampinus malabarica (L.) Merr. (II)]

Four chemical compounds isolated from the root of Gossampinus malabarica were identified as daucosterol, oleanolic acid, hesperidin and potassium nitrate by physico-chemical constants and spectroscopic analysis.

Speaker identification using time-delay HMEs

In this paper, we extend the Hierarchical Mixture of Experts (HME) to temporal processing and explore it for a substantial problem, that of text-dependent speaker identification. For a specific multiway classification, we propose a generalized Bernoulli density instead of the multinomial logit density to avoid the instability during training. Time-delay technique is applied for spatio-temporal processing in the HME and a combining scheme is presented for combining multiple time-delay HMEs in order to complete a multi-scale analysis for the temporal data. Using the time-delay HME along with the EM algorithm as well as the combination of multiple time-delay HMEs, the speaker identification system has a good performance and yields significantly fast training. We have also addressed some issues about the time-delay techniques in the HME.

Preparation of glass ionomer cement using N-acryloyl-substituted amino acid monomers--evaluation of physical properties

OBJECTIVES

The objectives of this study were (1) to develop polyacid formulations through the incorporation of amino acid-derived monomers with carboxylic acid groups at various distances away from the polymer backbone to allow for greater flexibility, less rigid ionic cluster formation and improved solubility, and (2) to test selected physical and handling properties of experimental ionomers with a conventional glass ionomer as a control.

METHODS

The polycarboxylic acids prepared and used in glass ionomer formulation in this study included N-acryloylglutamic acid (AGA) and N-acryloyl-6-aminocaproic acid (AACA)- modified acrylic acid- ++itaconic acid copolymers, where the acrylic acid:itaconic acid:amino acid monomers were combined in different proportions. The characterization and purity of the monomers were determined by FTIR and their melting points. The characterization of synthesized polymers included molecular weight and relative viscosity determinations. The compressive strengths, diametral tensile strengths, flexural strengths and fracture toughness of the experimental ionomers and a commercially available ionomer (control) were measured after storage in water, at 37 degrees C for 1 h or 7 d. The working times and setting times of the experimental ionomers were compared to the control specimens. Separate analysis of variance and Tukey's tests were used to study the statistical significance of the physical strength parameters as a function of materials and storage times.

RESULTS

Significant increases (p< 0.001) in diametral tensile, compressive, flexural strengths and fracture toughness were observed in the AGA co-polymers, while significant increases were observed in diametral and flexural strengths in the AACA co-polymers compared to the control Fuji II. The working and setting times of all except one experimental ionomer studied were comparable to the controls.

SIGNIFICANCE

The use of amino acid-modified acrylic monomers to produce water soluble copolymers of acrylic-itaconic acid offers a new route of discovery to produce chemical-cured glass ionomers with improved physical properties. The spacer chain length, the hydrophobicity of the chains, the molecular weight and viscosity of the polymer all played important roles in determining the physical properties of the material.

Coi1-dependent expression of an Arabidopsis vegetative storage protein in flowers and siliques and in response to coronatine or methyl jasmonate

The phytotoxin coronatine and the plant growth regulator methyl jasmonate (MeJA) inhibit the growth of Arabidopsis seedlings. Coronatine and MeJA induced the accumulation of an approximately 29-kD protein in wild-type seedlings but not in seedlings of the coi1 mutant, which is insensitive to both compounds. The approximately 29-kD protein was recognized not only by antibodies raised against the partially purified polypeptide, but also by antibodies raised against vegetative storage proteins (VSPs) from soybean (29 kD) and poplar (32 kD). In the absence of added MeJA/coronatine, the VSP-like protein was highly expressed in flowers and siliques but not in seeds, seedlings, or mature leaves of wild-type Arabidopsis. By contrast, this protein could not be detected in coi1 seedlings treated with coronatine or MeJA, and it was found in very low levels in the male sterile flowers of coi1. A transcript corresponding to the gene of the Arabidopsis 27-kD VSP precursor shows the same pattern of expression as the VSP-like protein. Significantly, the VSP-like protein was not detected in green siliques or seeds obtained from coi1 flowers fertilized with wild-type pollen. We conclude that the VSP-like protein is normally expressed in maternal tissues, where it is regulated by COI1, but is not essential for the development of siliques.

[Cryosurgical resection of pulmonary metastases (experience of twenty years)]

Cryosurgical resection of pulmonary metastases was performed in 112 patients from 1973 to 1993. The cumulative 1, 3, 5, 10 year survival rate was 80.37%, 41.81%, 28.01% and 17.28%. One patient died of respiratory failure after operation. Thirty-day mortality rate was 0.89%. The disease-free interval (DFI) between the control of primary tumor and appearance of metastases was significantly correlated with post-thoracotomy survival. The multiple factor analysis also demonstrated that DFI was the most important prognostic factor for patients after cryosurgical resection of pulmonary metastatic lesions. The overall 5 year survival rate of patients treated with cryosurgery in our report was higher than that of those treated by local resection of pulmonary metastases reported by other authors. Our results indicated that cryosurgical resection of pulmonary metastases was effective and safe, the survival time of most patients could be prolonged and some patients could be cured.

The heat capacity of proteins

The heat capacity plays a major role in the determination of the energetics of protein folding and molecular recognition. As such, a better understanding of this thermodynamic parameter and its structural origin will provide new insights for the development of better molecular design strategies. In this paper we have analyzed the absolute heat capacity of proteins in different conformations. The results of these studies indicate that three major terms account for the absolute heat capacity of a protein: (1) one term that depends only on the primary or covalent structure of a protein and contains contributions from vibrational frequencies arising from the stretching and bending modes of each valence bond and internal rotations; (2) a term that contains the contributions of noncovalent interactions arising from secondary and tertiary structure; and (3) a term that contains the contributions of hydration. For a typical globular protein in solution the bulk of the heat capacity at 25 degrees C is given by the covalent structure term (close to 85% of the total). The hydration term contributes about 15 and 40% to the total heat capacity of the native and unfolded states, respectively. The contribution of non-covalent structure to the total heat capacity of the native state is positive but very small and does not amount to more than 3% at 25 degrees C. The change in heat capacity upon unfolding is primarily given by the increase in the hydration term (about 95%) and to a much lesser extent by the loss of noncovalent interactions (up to approximately 5%).(ABSTRACT TRUNCATED AT 250 WORDS)

The oligodendroglial reaction to brain stab wounds: an immunohistochemical study

Myelin/oligodendrocyte specific protein was compared to glial fibrillary acidic protein and 2'3'-cyclic nucleotide 3'-phosphodiesterase expression in normal rat brains and following stab wounds to the cerebral cortex, corpus callosum and hippocampus. Animals with stab wounds were allowed to recover for 5, 15, 28, 45 and 70 days post-operation before fixation by perfusion. Sections were reacted with antibodies against myelin/oligodendrocyte specific protein, glial fibrillary acidic protein and 2'3'-cyclic nucleotide 3'-phosphodiesterase, and observed by light and electron microscopy. Normal cerebral cortex had very few myelin/oligodendrocyte specific protein-positive and 2'3'-cyclic nucleotide 3'-phosphodiesterase-positive cells, but some glial fibrillary acidic protein-positive cells. The myelinated fibres of the corpus callosum were heavily stained for myelin/oligodendrocyte specific protein but unstained by glial fibrillary acidic protein or 2'3'-cyclic nucleotide 3'-phosphodiesterase antibodies. Some immunopositive cells were present in the corpus callosum and hippocampus with all three antibodies. After stab wound myelin/oligodendrocyte specific protein-positive reactive cells had more and longer processes and stained more intensely than equivalent cells in normal brain. These cells were distributed along the wound track, including within the cerebral cortex. The numbers of these cells increased until 28 days post-operation and then decreased so that very few were found at 70 days post-operation except in the corpus callosum. Where demyelination occurred myelin/oligodendrocyte specific protein-staining was lost. Staining for 2'3-cyclic nucleotide 3'-phosphodiesterase revealed a similar pattern. Glial fibrillary acidic protein-positive reactive cells, which were also more robust than the normal cells, were more widely distributed. They increased in number throughout the time periods studied and gliosis was evident on the contralateral side. The glial fibrillary acidic protein-positive astrocytes were also different from the myelin/oligodendrocyte specific protein-positive and 2'3'-cyclic nucleotide 3'-phosphodiesterase-positive oligodendrocytes in terms of cell shape. With electron microscopy myelin/oligodendrocyte specific protein-positive cells showed features typical of immature oligodendrocytes. We conclude that the injury caused a numerical increase in oligodendrocytes and that myelin/oligodendrocyte specific protein is a good marker for the oligodendroglial response and demyelination in pathological conditions.

Intracoronary ultrasound following excimer-laser angioplasty. An in-vitro study in human coronary arteries

To study the ablation effects induced by excimer laser coronary angioplasty (ELCA), we examined 41 segments of nine isolated coronary arteries. An electronic intracoronary ultrasound device (ICUS: 20 MHz, 3.5F, Endosonics) was positioned coaxially within the vessel. Angioplasty was performed using a 1.7 mm ELCA catheter (Spectranetics) which was placed in the lumen and directed vertically onto the intimal surface of the vessel (fluence: 10-50 mJ.mm-2). The laser catheter was removed after each lasing cycle to allow the stepwise evaluation of the morphological effects of ELCA and to avoid reaching the adventitia. Ultrasound images were compared with the corresponding histological specimens. In all cases, the ablation site could be correctly identified by ICUS. No penetration of the adventitia was seen at histology. Ablation depth was 0.31 +/- 0.18 mm as determined by histology and 0.34 +/- 0.18 mm as determined by ultrasound; the diameter of the crater was 0.63 +/- 0.21 mm, and 0.75 +/- 0.16 mm, respectively, and wall thickness was 0.68 +/- 0.18 mm, and 0.83 +/- 0.20 mm, respectively. A statistical relationship between ultrasonic and histology measurements was only found, however, for assessment of wall thickness (r = 0.71).

CONCLUSIONS

The identification of small ablation effects by ICUS was possible with great accuracy and ELCA could be performed without penetration of the adventitial layers. However, exact quantification of the crater dimensions was not possible due to limitations of the axial and lateral resolution. Thus, for the guidance of ELCA by ICUS a further improvement in the resolution capabilities of ICUS devices is mandatory.

Thermodynamic characterization of an equilibrium folding intermediate of staphylococcal nuclease

High-sensitivity differential scanning calorimetry and CD spectroscopy have been used to probe the structural stability and measure the folding/unfolding thermodynamics of a Pro117-->Gly variant of staphylococcal nuclease. It is shown that at neutral pH the thermal denaturation of this protein is well accounted for by a 2-state mechanism and that the thermally denatured state is a fully hydrated unfolded polypeptide. At pH 3.5, thermal denaturation results in a compact denatured state in which most, if not all, of the helical structure is missing and the beta subdomain apparently remains largely intact. At pH 3.0, no thermal transition is observed and the molecule exists in the compact denatured state within the 0-100 degrees C temperature interval. At high salt concentration and pH 3.5, the thermal unfolding transition exhibits 2 cooperative peaks in the heat capacity function, the first one corresponding to the transition from the native to the intermediate state and the second one to the transition from the intermediate to the unfolded state. As is the case with other proteins, the enthalpy of the intermediate is higher than that of the unfolded state at low temperatures, indicating that, under those conditions, its stabilization must be of an entropic origin. The folding intermediate has been modeled by structural thermodynamic calculations. Structure-based thermodynamic calculations also predict that the most probable intermediate is one in which the beta subdomain is essentially intact and the rest of the molecule unfolded, in agreement with the experimental data. The structural features of the equilibrium intermediate are similar to those of a kinetic intermediate previously characterized by hydrogen exchange and NMR spectroscopy.

Structure based prediction of protein folding intermediates

The complete unfolding of a protein involves the disruption of non-covalent intramolecular interactions within the protein and the subsequent hydration of the backbone and amino acid side-chains. The magnitude of the thermodynamic parameters associated with this process is known accurately for a growing number of globular proteins for which high-resolution structures are also available. The existence of this database of structural and thermodynamic information has facilitated the development of statistical procedures aimed at quantifying the relationships existing between protein structure and the thermodynamic parameters of folding/unfolding. Under some conditions proteins do not unfold completely, giving rise to states (commonly known as molten globules) in which the molecule retains some secondary structure and remains in a compact configuration after denaturation. This phenomenon is reflected in the thermodynamics of the process. Depending on the nature of the residual structure that exists after denaturation, the observed enthalpy, entropy and heat capacity changes will deviate in a particular and predictable way from the values expected for complete unfolding. For several proteins, these deviations have been shown to exhibit similar characteristics, suggesting that their equilibrium folding intermediates exhibit some common structural features. Employing empirically derived structure-energetic relationships, it is possible to identify in the native structure of the protein those regions with the higher probability of being structured in equilibrium partly folded states. In this work, a thermodynamic search algorithm aimed at identifying the structural determinants of the molten globule state has been applied to six globular proteins; alpha-lactalbumin, barnase, IIIGlc, interleukin-1 beta, phage T4 lysozyme and phage 434 repressor. Remarkably, the structural features of the predicted equilibrium intermediates coincide to a large extent with the known structural features of the corresponding intermediates determined by NMR hydrogen-exchange experiments.

Estimation of changes in side chain configurational entropy in binding and folding: general methods and application to helix formation

Theoretical estimations of changes in side chain configurational entropy are essential for understanding the different contributions to the overall thermodynamic behavior of important biological processes like folding and binding. The configurational entropy of any given side chain in any particular protein can be evaluated from the complete energy profile of the side chain. Calculations of the energy profiles can be performed using the side chain single bond dihedrals as the only independent variables as long as the structures at each value of the dihedrals are allowed to relax through small changes in the valence bond angles. The probabilities of different side chain conformers obtained from these energy profiles are very similar to the conformer populations obtained by analysis of side chain preferences in the proteins of the Protein Data Bank. Also, side chain conformational entropies obtained from the energy profiles agree extremely well with those obtained from the Protein Data Bank conformer populations. Changes in side chain configurational entropy in binding and folding can be computed as differences in conformational entropy because, in most cases, the frequency of the rotational oscillation around the energy minimum of any given conformer does not appear to change significantly in the reactions. Changes of side chain conformational entropy calculated in this way were compared with experimental values. The only available experimental data--the effect of side chain substitution on the stability of alpha-helices--were used for this comparison. The experimental values were corrected to subtract the solvent contributions. This comparison yields an excellent agreement between calculated and experimental values, validating not only the theoretical estimates but also the separability of the entropic contributions into configurational terms and solvation related terms.

Normal sequences of muscarinic acetylcholine receptors (m1 and m2) in patients with Alzheimer's disease and vascular dementia

The genes for muscarinic acetylcholine receptors, m1 and m2, were studied in autopsied brains from nine Alzheimer's disease, six vascular dementia and three control. The genes were amplified by the polymerase chain reaction and sequenced by the dideoxy method. Although one DNA polymorphism was found in m1, the deduced amino acid sequences of the muscarinic acetylcholine receptor were unchanged. The amino acid sequences of m1 and m2 in Alzheimer's disease and vascular dementia were intact.

Thermodynamic prediction of structural determinants of the molten globule state of barnase

Recently, it has been demonstrated that the enthalpy and heat capacity changes for protein folding/unfolding can be predicted rather accurately from the crystallographic or NMR solution structure of a protein. (K.P. Murphy, V. Bhakuni, D. Xie and E. Freire, Mol. Biol. 227 (1992) 293-306.) Under some conditions proteins do not unfold completely, giving rise to states in which the molecule remains in a compact configuration after denaturation. These compact denatured or molten globule states retain a hydrophobic core, exhibit residual structure and a compactness close to that of the native state. This phenomenon is reflected in the thermodynamics of the process. By using the structural parametrization of the energetics, it is possible to develop an algorithm aimed at selecting partly folded states that conform to the experimental thermodynamic constraints of the molten globule. We have applied our molten globule search algorithm to the globular protein barnase. This approach has allowed a structure based selection of a unique family of structural states that satisfy the experimental criteria of the molten globule. The prediction of the molten globule search algorithm indicates that the first helix together with most of the beta-sheet structure (beta 2, beta 3-5) and loop 5 constitute the main determinants of the molten globule intermediate, in agreement with the NMR data. These results open the prospect for an automated search of the structural determinants of the molten globule state of proteins and suggest that solvation parameters can be effectively used to probe structural states of proteins.

Molecular basis of cooperativity in protein folding. V. Thermodynamic and structural conditions for the stabilization of compact denatured states

The heat-denatured state of proteins has been usually assumed to be a fully hydrated random coil. It is now evident that under certain solvent conditions or after chemical or genetic modifications, the protein molecule may exhibit a hydrophobic core and residual secondary structure after thermal denaturation. This state of the protein has been called the "compact denatured" or "molten globule" state. Recently is has been shown that alpha-lactalbumin at pH < 5 denatures into a molten globule state upon increasing the temperature (Griko, Y., Freire, E., Privalov, P.L. Biochemistry 33:1889-1899, 1994). This state has a lower heat capacity and a higher enthalpy at low temperatures the stabilization of the molten globule state is of an entropic origin since the enthalpy contributes unfavorably to the Gibbs free energy. Since the molten globule is more structured than the unfolded state and, therefore, is expected to have a lower configurational entropy, the net entropic gain must originate primarily from solvent related entropy arising from the hydrophobic effect, and to a lesser extent from protonation or electrostatic effects. In this work, we have examined a large ensemble of partly folded states derived from the native structure of alpha-lactalbumin in order to identify those states that satisfy the energetic criteria of the molten globule. It was found that only few states satisfied the experimental constraints and that, furthermore, those states were part of the same structural family. In particular, the regions corresponding to the A, B, and C helices were found to be folded, while the beta sheet and the D helix were found to be unfolded. At temperatures below 45 degrees C the states exhibiting those structural characteristics are enthalpically higher than the unfolded state in agreement with the experimental data. Interestingly, those states have a heat capacity close to that observed for the acid pH compact denatured state of alpha-lactalbumin [980 cal (mol.K)-1]. In addition, the folded regions of these states include those residues found to be highly protected by NMR hydrogen exchange experiments. This work represents an initial attempt to model the structural origin of the thermodynamic properties of partly folded states. The results suggest a number of structural features that are consistent with experimental data.

The middle-aged generation is at high risk for suicide in Japan. A comparison between the 1950s and the 1980s

The suicide rate in Japan was the highest in the world the 10 years after World War II. There were many suicides among young and aged people. Now, Japan has many suicides among middle-aged people, and suicides among elderly people are still remarkable. These findings suggest that middle-aged people in 1980s have a high risk of suicide and that suicide among elderly people will increase in 10-20 years.

Molecular mutagenesis induced by glycidyl methacrylate

Glycidyl methacrylate (GMA) is a recently recognized mutagen. In order to explore the mutagenicity and mechanism of GMA, plasmid pBR322 was used for in vitro binding, mutant screening, restriction enzyme mapping, and DNA sequencing. To explore the mechanism by which an initial premutational event is converted into a stable heritable mutation, pBR322 and GMA-bound pBR322 were transformed into E. coli HB101, and the following results were obtained: 1) GMA-bound pBR322 induced phenotype changes in competent cells. Two stable and heritable mutants were isolated (ApRTcS and ApSTcR). 2) When restriction enzyme mapping was used to analyze the mutant ApRTcS, four of seven maps showed changes, but no large DNA insertion or deletion were observed. 3) The frequency of deletion and insertion forms counted about 10%. Sequence specificity and hot spot regions were evident in the sequence analysis of mutated plasmid. The above results indicate that the premutagenic lesions of plasmid induced by GMA can be converted into point mutations in vivo.

Entropy in biological binding processes: estimation of translational entropy loss

The loss of translational degrees of freedom makes an important, unfavorable contribution to the free energy of binding. Examination of experimental values suggest that calculation of this entropy using the Sackur-Tetrode equation produces largely overestimated values. Better agreement is obtained using the cratic entropy. Theoretical considerations suggest that the volumes available for the movement of a ligand in solution and in a complex are rather similar, suggesting also that the cratic entropy provides the best estimate of the loss of translational entropy.

Fibronectin fragments alter matrix protein synthesis in cartilage tissue cultured in vitro

We reported earlier that fibronectin fragments (Fn-f) added to bovine articular cartilage cultured in serum-free culture causes marked protease expression with resultant proteoglycan (PG) degradation and release into the culture media. We have further characterized the effects of Fn-f by studies of the effects on proteoglycan, collagen, general protein, and DNA synthesis and reversibility of the cartilage damage. We report here that the most active Fn-f, a 29-kDa amino-terminal Fn-f, when added to a 1 microM concentration, depressed PG and general protein synthesis in cartilage by over 50% within 24 h, as measured by sulfate and methionine/cysteine incorporation, respectively. This same Fn-f decreased PG synthesis throughout the full thickness cartilage section as shown by autoradiography. PG and general protein synthesis were significantly depressed within 24 h by 29-kDa Fn-f concentrations as low as 10 nM. Synthesis rates were effected by 100-fold lower Fn-f concentrations than was induction of proteinases. Removal of the 29-kDa Fn-f allowed a gain to supernormal levels of PG and protein synthesis. Cartilage damaged to the extent of removal of over 50% of the total PG did not replace PG after over 4 weeks in 10% serum-Dulbecco's modified Eagle minimum with or without added TGF-b1 and rIGF-a. These data show that while the effects of Fn-f on elevating protease expression and depressing PG synthesis are reversible, the resultant cartilage damage is apparently irreversible in vitro. Therefore, if Fn-f-mediated cartilage damage occurs as part of cartilage disease processes, the pathologic effects would be quite significant.