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Biomedical subjects

A Ripamonti

Publications and source records attributed to A Ripamonti.

At least 19 recordsLinked to original sources
PubMed1999

Crystallization and preliminary X-ray study of chloroplast glyceraldehyde-3-phosphate dehydrogenase.

Glyceraldehyde-3-phosphate dehydrogenase from spinach chloroplasts has been crystallized by vapour diffusion in the pH range 7-8.5 in (NH4)2SO4 and Tris-HCl buffer or potassium phosphate buffer at room temperature. Crystals of the A4 isoform, grown at pH 8.5 in Tris-HCl buffer, diffract to 3.0 A (at 100 K) using synchrotron radiation. The crystals belong to the orthorhombic C222 space group, with unit-cell dimensions a = 145.9, b = 185.9 and c = 106.3 A, and probably contain one tetramer per asymmetric unit. Structure determination by molecular replacement is in progress.

Chloroplasts↗
PubMed1998

X-ray diffraction and polarizing optical microscopy investigation of the structural organization of rabbit tibia.

X-ray diffraction and polarized optical microscopy investigations were carried out on thin sections of rabbit tibia in order to study the morphological organization of the structural components of this tissue, which often is utilized to test bone response to implants. In the optical microscope, the lateral face as well as the lateral portion of the caudal face exhibit a lamellar structure with an alternation of dark and bright lamellae running parallel to the long axis of the tibia. In contrast, both in the medial face and in the medial portion of the caudal face there are numerous osteonic structures. In spite of the complexity of this morphological organization, the results of small- and high-angle X-ray diffraction analyses indicate that the structural relationship between collagen fibrils and inorganic crystals is quite similar to that observed in single osteons and allows evaluation of the orientation of the two main structural components. Both collagen fibrils and apatitic crystallites are preferentially oriented parallel to the long axis of the tibia. The degree of orientation is greater in the thickness than in the plane of the lamellae, suggesting that collagen fibrils and inorganic crystallites lie preferentially in the plane of the lamellae, where they follow an oblique course. The degree of orientation of the apatitic crystallites is higher in the lateral face than in the medial and caudal faces, in agreement with the optical microscopic images. The results provide information that must be taken into account when evaluating the structural modifications of bone due to the insertion of a prosthetic device.

Animals↗
PubMed1998

X-ray diffraction on cyclically loaded osteons.

The results of a study on the fine structural distortion due to the two previously observed types of degradation in cyclically loaded single osteons (i.e., stiffness degradation and pinching effect) are presented. Fully calcified longitudinal and alternate osteons were isolated from 350-microns-thick longitudinal sections of human femoral cortical bone. The samples were prepared from 500-microns-long central cylindrical portions of an osteon, whose two ends were penetrating into rectangular lugs for fixation to an electromechanical device that cyclically loaded the samples. This device was connected to a microwave micrometer and a recorder. The structural distortions induced by cyclic loading were investigated by high- and low-angle X-ray diffraction on conventional and synchrotron radiation sources. Cyclic loading results in a reduction in the degree of orientation of apatite crystallites, especially in longitudinal osteons, in which the most abundant longitudinal lamellae are not protected against buckling by transverse lamellae as they are in alternate osteons. In contrast, the degree of orientation of collagen fibrils does not seem to be affected by cycling loading in the two osteon types, possibly because the disorientation of collagen fibrils is, within limits, a reversible process. Finally, the contrast between the disorientation of inorganic crystallites and the apparently unaltered distribution of collagen fibrils suggests that the degradation of cyclically loaded osteons may be due to a separation of the crystallites from the fibrils.

Adult↗
PubMed1997

Chemical and structural characterization of the mineral phase from cortical and trabecular bone.

X-ray diffraction, infrared spectroscopy and chemical investigations have been carried out on the inorganic phases from rat cortical and trabecular bone. Although both inorganic phases consist of poorly crystalline B carbonated apatite, several significant differences have been observed. In particular, trabecular bone apatite displays reduced crystallite sizes, Ca/P molar ratio, and carbonate content, and exhibits a greater extent of thermal conversion into beta-tricalcium phosphate than cortical bone apatite. These differences can be related to the different extents of collagen posttranslational modifications exhibited by the two types of bone, in agreement with their different biological functions.

Animals↗
PubMed1992

The role of magnesium on the structure of biological apatites.

X-ray diffraction, infrared absorption spectroscopy, and chemical investigation have been carried out on deproteinated samples of turkey leg tendon at different degrees of calcification. The inorganic phase consists of poorly crystalline B carbonated apatite. On increasing calcification, the apatite crystal size, as well as its thermal stability, increase while the relative magnesium content is reduced. On the other hand, synchrotron X-ray diffraction data clearly indicate that apatite lattice parameters do not change as the crystals get larger. At the last stage of calcification the crystal size, chemical composition, and thermal conversion of the apatite crystallites approximate those of bone samples, which have been examined for comparison. The results provide a quantitative relationship between relative magnesium content and extent of apatite conversion into B-tricalcium phosphate by heat treatment. Furthermore, they suggest that the smaller crystallites laid down inside the gap region of the collagen fibrils are richer in magnesium than the longer ones that fill the space between collagen fibrils.

Animals↗
PubMed1991

Structural analysis of turkey tendon collagen upon removal of the inorganic phase.

Calcified leg flexor tendons in which the inorganic phase content had been lowered by progressive demineralization were studied by small angle X-ray diffraction and thermogravimetry. The X-ray diffraction results agree very well with the data previously obtained on calcified turkey tendon indicating that the method used to decalcify tendons provides good correspondence with the process of calcification. Up to five thermal processes can be detected in the thermogravimetric scans: (1) water release; (2) collagen decomposition; (3 and 4) combustion of the residual organic components; (5) carbonate removal from the apatitic phase. The temperature of collagen decomposition decreases at lower inorganic phase content in agreement with the higher thermal stability of calcified collagen fibrils compared with uncalcified ones. The decrease of collagen thermal stability upon decalification is paralleled by a decrease of the structural order of the collagen fibrils as indicated by small angle X-ray diffraction data. Decalcification down to about 40% wt of inorganic phase does not significantly alter the inorganic blocks that are regularly arranged inside the gap zone of the collagen. Further removal of inorganic phase down to about 15% wt provokes a variation of the intensity distribution of the small angle meridional reflections that can be ascribed to a reduction of the mean height of the inorganic blocks. At inorganic phase contents below 15% wt the gap region is more free to contract upon air drying as a result of the reduction of the mean length of the inorganic blocks.

Animals↗
PubMed1991

Collagen structural organization in uncalcified and calcified human anterior longitudinal ligament.

Collagen structure and collagen-apatite structural relationship has been investigated in human anterior ligament, where the mineral deposition occurs on collagen fibrils morphologically different from those of bone and tendons. Ultrastructural observations made on replicas of cryoprotected and freeze fractured uncalcified samples display a "helicoidal" morphology of the collagen fibrils. X-ray diffraction analysis carried out using conventional and synchrotron radiation sources revealed that the D-axial spacing is 65.0 nm and the electron density distribution inside the repeating period is very similar to those of tendon collagen in the same conditions of hydration. The short D-period can be interpreted as due to a greater angle of molecular crimping and/or molecular tilt compared to that of tendon. Air drying does not cause any appreciable variation in the D-axial period and induces an increase of the gap/overlap ratio that can be ascribed to telopeptide disorder. In spite of the different morphology of the collagen fibrils, the structural relationship between collagen and the mineral phase in calcified ligament is very close to that observed in bone and tendons. The apatitic phase is laid down in blocks along the collagen fibrils with the same axial periodicity, D = 65.0 nm, as that of uncalcified collagen fibrils. The mean height of the mineral blocks, which are 0.45D long, is even higher than in bone and masks any further fluctuation of the electron density due to the organic matrix.

Calcinosis↗
PubMed1990

Thermal conversion of octacalcium phosphate into hydroxyapatite.

The thermal conversion of octacalcium phosphate into hydroxyapatite has been investigated by a crystallographic, thermogravimetric, and calorimetric study. The conversion of octacalcium phosphate takes place through the remotion of three of its five water molecules and yields a poor crystalline apatitic phase. The three water molecules are lost in two steps. The first one, which is reversible, corresponds to the remotion of one water molecule and induces a slight contraction of the unit cell of OCP. The successive remotion of two water molecules, which provokes the structural conversion of OCP into apatite, is in irreversible process. The mechanism of the water loss of OCP is explained in terms of its crystal structure.

Calcium Phosphates↗
PubMed1990

NMR monitoring of the anaerobic metabolism of frog muscle at rest.

The time dependence of Lactate (Lac), H+, Adenosine-triphosphate (ATP), Phosphocreatine (PCr), Hexose-monophosphate (PME), and Inorganic Phosphate (Pi) levels has been obtained for frog muscle at rest in anaerobic conditions by multinuclear NMR. All information has been collected on the same samples alternatively tuning the probehead on 1H- and 31P-NMR frequencies. ATP, PCr and H+ levels show the same time dependence for all the samples, while PME, Pi and Lac levels vary in time differently from one sample to another. No direct correlation between the Lac appearance and the H+ concentration has been found.

Adenosine Triphosphate↗
PubMed1988

Structural and chemical characterization of inorganic deposits in calcified human mitral valve.

X-ray diffraction, i.r. absorption, and chemical analyses have been carried out on the mineral deposits of calcified human mitral valves and glutaraldehyde-preserved porcine aortic grafts. The mineral deposits isolated from highly calcified mitral valves and porcine aortic grafts are constituted of type B-carbonate apatite. Magnesium substituted beta-tricalcium phosphate is present, together with an apatitic phase similar to dahllite, in the ashes of poorly calcified mitral valves. The contraction of the unit cell of beta-tricalcium phosphate due to magnesium incorporation is compared with the variation of the lattice constants of synthetic beta-tricalcium phosphate at different degree of magnesium substitution for calcium. The results reveal the important role of magnesium on the calcification of human valves. In fact, the apatitic phase deposited at the beginning of the calcification process, when there is a high magnesium content, converts completely into beta-tricalcium phosphate by heat treatment at 1,000 degrees C. On the other hand, when the calcification becomes massive, magnesium content appears highly reduced, and the deposited apatitic phase is characterized by a high thermal stability.

Calcinosis↗
PubMed1986

Pattern recognition of sequence similarities in globular proteins by Fourier analysis: a novel approach to molecular evolution.

A new algorithm is introduced for analyzing gene-duplication-independent (orthologous) and gene-duplication-dependent amino acid sequence similarities between proteins of different species. It is based on the calculation of an autocorrelation function D(x) as a Fourier series analogous to that used in crystal analysis by x-ray diffraction. The primary structure of the protein is decomposed into "homopolypeptide-defective sequences" containing identical or similar amino acid residues and vacancies corresponding to the missing amino acid residues. The Fourier transforms F(h) simulating the diffraction patterns of defective linear gratings corresponding to the defective homopolypeptide sequences are calculated. The squared F(h) values are then used as coefficients of Fourier series corresponding to the autocorrelation functions D(x). A peak of D(x) corresponds to a vector of length x, which is the distance between two identical amino acid residues. It is pointed out that optical diffraction methods, instead of computer methods, would also be useful. It is shown through a number of examples that this method allows satisfactory pattern recognition of homologies and internal duplications of an initial segment of the polypeptide chain. In the latter case the value of the above method may be seen from the fact that it detects repeated duplications in proteins such as spinach ferredoxin and myoglobin, for which other methods had either failed or given inconclusive results. The above approach appears most promising for studies of molecular evolution and structure-sequence correlations.

Amino Acid Sequence↗
PubMed1985

Metabolic fate of zetidoline, a new neuroleptic agent, in man.

Healthy volunteers administered orally a single dose (20 mg) of [2-14C]zetidoline, a new dopamine antagonist, exhibited rapid absorption of radioactivity with peak plasma levels of 250-300 ng/ml achieved in 1 h. The compound underwent intensive metabolic first-pass so that plasma radioactivity was represented mostly by two products, metabolite B endowed with neuroleptic activity, and metabolite D inactive, while unchanged zetidoline was not detected. Disappearance of radioactivity from plasma was rapid with a half-life of 1.78 +/- 0.20 h. The simultaneous assay of plasma prolactin showed increased levels of the hormone (+ 464% at the peak time) up to the 6th h after dosing, with plasma concentration profile which mimic those of metabolite B. The radioactive test-dose was eliminated mainly via the kidneys with an average urinary recovery of 84.7 +/- 1.7% in 4 days (73.4 +/- 1.1% within 8 h). The main urinary metabolite (metabolite G) and two minor ones (metabolites B and D) were purified and their structures assigned by IR, MS and NMR spectroscopy, they are: 1-(3-chloro-4-hydroxyphenyl)-3 [2-(3,3-dimethyl-1-azetidinyl)ethyl]imidazolidin-2-one, metabolite B; 1-[2-(3,3-dimethyl-1-azetidinyl)ethyl]-imidazolidin-2-one, metabolite D and the 4'-O-sulphate ester of metabolite B, metabolite G. The metabolic fate of zetidoline in man follows the same phase I reactions demonstrated in rats and dogs, while the phase II reaction is sulphoconjugation instead of the glucuronidation observed in animals.

Adult↗
PubMed1985

A low-angle X-ray diffraction analysis of osteonic inorganic phase using synchrotron radiation.

Using synchrotron radiation the low-angle X-ray diffraction method has been applied to single osteon samples to yield new data on the texture of the inorganic bone fraction. Two sample types--cylindrically shaped osteonic samples and osteonic radial hemisections--were prepared from longitudinal and alternate osteons at both the initial and final stages of calcification. The results indicate that the diffraction pattern is due to the inorganic phase, which reveals the same axial periodicity as native collagen fibrils and fits into the main band. No change is appreciable as osteons pass from the initial to the final stage of calcification. This means that when crystallites covering much more than a collagen axial period are observed under the electron microscope, they do not appreciably affect the calcified banding of collagen fibrils. The osteonic axis corresponds to the main direction of collagen orientation both in longitudinal and alternate osteons. The degree of orientation, however, is lower in alternate osteons than in longitudinal ones, where only few thin, incomplete transversal lamellae are found.

Adult↗
PubMed1985

Metabolic pathways of the anti-hypertensive agent, N-(2,5-dimethyl-1H-pyrrol-1-yl)-6-(4-morpholinyl)-3-pyridazinamine+ ++ hydrochloride. I. Studies in the rat.

The metabolic fate of a new anti-hypertensive, 1-pyrrolyl pyridazinamine, was studied in male Wistar rats after both p.o. and i.v. administration (1 mg/kg). The compound undergoes rapid metabolism, disappearing from the central compartment with a half-life of about 0.5 h. Plasma concn. of the parent drug and its major metabolite I following i.v. and p.o. administration suggest a route-dependent first-pass metabolism. Ten metabolites were isolated from the urine and identified by u.v., i.r., mass and 1H-n.m.r. spectroscopy. The structure of some was confirmed by 13C-n.m.r. and chemical synthesis. All biotransformations are restricted to the pyrrole ring which undergoes oxidative cleavage followed by a series of chemical rearrangements. A minor pathway leads to the formation of methyl sulphinyl and methyl sulphonyl pyrroles. It is suggested that, as with natural indoles, the pyrrole might be oxidized by a 2,3-dioxygenase. The three major metabolites, I, II and IX, along with two minor ones, VI and VII, were inactive when tested i.v. for antihypertensive activity.

Administration, Oral↗
PubMed1985

Metabolic pathways of the anti-hypertensive agent, N-(2,5-dimethyl-1H-pyrrol-1-yl)-6-(4-morpholinyl)-3-pyridazinamine hydrochloride. II: Studies in the dog.

The metabolic fate of a new anti-hypertensive, 1-pyrrolyl-pyridazinamine, was studied in male Beagle dogs given both p.o. and i.v. doses of the 14C-labelled drug (1 mg/kg). The compound given as a single i.v. injection disappeared from the central compartment with a half-life of about 0.9 h. Plasma levels of total 14C were represented mostly by metabolites. Eight urinary metabolites designated as metabolites I, II and XI-XVI were purified and their structures assigned by means of u.v., i.r., n.m.r. and mass spectrometry. Quantitatively the primary metabolic attack involved the morpholine moiety of the molecule which undergoes oxidative opening. A minor pathway afforded the cleavage of the pyrrole followed by chemical rearrangements to form six-membered sidnone-like products or a triazole derivative. The major (XIII) and three minor metabolites were studied for their antihypertensive activity in rats and were shown to be inactive.

Administration, Oral↗
PubMed1984

Thermal behavior of bone and synthetic hydroxyapatites submitted to magnesium interaction in aqueous medium.

The thermal behavior of the products obtained from magnesium interaction with powdered femoral bone and carbonate containing synthetic hydroxyapatite under conditions of pH fluctuation in aqueous medium has been investigated. The products, heat treated at different temperatures from 100 to 1300 degrees C, have been characterized by infrared spectroscopy and X-ray diffraction technique. The results show that the interaction with magnesium ion destabilizes the apatitic structure and favours its thermal conversion into beta-tricalcium phosphate (beta-TCP). The replacement of magnesium with calcium in the beta-TCP crystal lattice hinders its subsequent thermal conversion into the alpha form. The influence of magnesium on the thermal stability is much more evident for carbonate-containing synthetic hydroxyapatite than for bone apatite.

Animals↗