Biomedical subjects

A Morros

Publications and source records attributed to A Morros.

6 recordsLinked to original sources

PubMed2000

Cholesterol efflux promotes acrosome reaction in goat spermatozoa.

Cholesterol efflux and membrane destabilization play an important role in sperm capacitation and membrane fusion in the acrosome reaction (AR). In this study we establish the effect of cholesterol removal from spermatozoa on acrosomal responsiveness. Mature goat spermatozoa were incubated in BSA-free medium in the presence of beta-cyclodextrin (betaCD) as cholesterol acceptor. After incubation with 8 mM betaCD, 50-60% of cholesterol was released from sperm membranes with no loss in the phospholipid content, and 35% of AR was induced. However, when 30% of cholesterol was lost, this moderate cholesterol decrease was unable to initiate AR. Cholesterol desorption was very rapid, following an exponential kinetics with a half-time of around 10 min, which is in contrast with the slow sigmoidal kinetics of acrosomal responsiveness: around 2 h was required for maximal AR. Our results suggest that cholesterol efflux has a direct influence on the onset of the AR, that is, merely removing cholesterol would trigger the AR.

Acrosome↗

PubMed1996

Membrane lipid dynamics during human sperm capacitation.

Sperm membranes have an unusual lipidic composition which is distinct from those of mammalian somatic cells. They have high levels of plasmalogens, a kind of ether-linked lipids, and a high content of polyunsaturated fatty acyl groups. Plasmalogens may form non-diffusible membrane regions or domains, whereas polyunsaturated ethanolamine plasmalogens are known to destabilize the lipidic bilayer. During transit of sperm through the female reproductive tract, sperm-coating proteins bind to heparin-like glycosaminoglycans. An essential feature of capacitation is the removal of cholesterol from the acrosomal membrane of sperm. Albumin and high-density lipoproteins present in the uterine and follicular fluid act as cholesterol acceptors. Plasma membrane of sperm organize in large non-diffusible lipid domains. This regionalization affects the distribution of both lipids and proteins. A barrier to lateral diffusion of lipids and proteins in the equatorial segment has been reported and contributes to the formation of macrodomains. Lateral separation into cholesterol-rich and cholesterol-depleted microdomains could also be created. Cone-shaped phospholipids induce the formation of non-bilayer phases and might facilitate membrane fusion. This review will discuss the removal of coating proteins, cholesterol efflux, domain organization, relocalization of lipids and proteins and the role of fusogenic lipids during capacitation.

Acrosome↗

PubMed1991

Thermal transitions in the structure of tubulin. Environments of aromatic aminoacids.

The environment of aromatic aminoacids in the thermal transition of brain tubulin has been studied by several spectroscopic techniques (Fourth Derivative, Difference Absorption, Fluorescence and Circular Dichroism), in order to study its denaturation. An irreversible, temperature-induced, structural transition was found at around 48 degrees C. In order to establish the relative degree of hydrophobicity of tubulin aromatic residues, before and after the thermal transition, difference and fourth derivative absorption spectra at different temperatures were compared with spectra of tyrosine and tryptophan model compounds in different media. It was found that at high temperatures, tubulin acquires a partially denatured stable state, with a significant amount of residual structure still preserved. This state is characterized by a general increase of the exposure of tyrosine residues to the medium, while the environment of tryptophans becomes more hydrophobic.

Amino Acids↗

PubMed1985

Determination of heptaminol in plasma by thin-layer chromatography and in situ fluorimetry.

A method has been developed for the determination of heptaminol in plasma samples. The main steps involved in the assay are: ethereal extraction at an alkaline pH; concentration of the extracted heptaminol as its hydrochloride; formation of a fluorescent derivative by reaction with 4-chloro-7-nitrobenzo-2,1,3-oxadiazole; separation of the fluorophore by thin-layer chromatography and in situ quantitation of the emitted fluorescence by photodensitometry. The sensitivity limit is estimated to be 25 ng ml(-1) plasma, the overall recovery is 81% and the relative standard deviation is 6% at 200 ng ml(-1). The assay is useful in studies on the pharmacokinetics of heptaminol in animals or man after administration of therapeutic doses. Plasma levels of the drug following administration of 5 mg.kg(-1) to rats are reported.

Journal Article↗

PubMed1982

The state of tyrosine and phenylalanine residues in proteins analyzed by fourth-derivative spectrophotometry. Histone H1 and ribonuclease A.

The analysis of the absorption spectra of model compounds of tyrosine and phenylalanine residues by means of fourth-derivative spectrophotometry is able to separate the contribution of the two chromophores, thus allowing the study of each one. Fourth-derivative analysis resolves the two main vibrational bands of tyrosine, giving rise to two peaks which are sensitive to changes in the environment of the phenolic ring. The parameters obtained from the fourth-derivative spectra were found to depend on the strength of the hydrogen bonds formed by the OH group of tyrosine, as well as on the heterogeneity of tyrosine environments. It is also shown that the fourth-derivative tyrosine peaks are not perturbed by broad bands, such as that arising from ionized tyrosine chromophores. The peaks arising from the phenylalanine model, although less sensitive than those of tyrosine, were found to depend on the polarity of the environment. As a check of the method, it is applied to the study of tyrosine and phenylalanine residues of calf thymus histone H1 and bovine pancreatic ribonuclease A.

Animals↗

PubMed1977

Interactions of histones and histone peptides with DNA Thermal denaturation and solubility studies.

The interactions of DNA with the five histone components (H1, H2B, H2A, H3 and H4) and with a number of histone fragments (N-H1 (1--72), C-H1 (73--216), N-H2B (l--59), C-H2B, (63--125), N-H2A (1-39), C-H2A (58--129), N-H4 (1--84) and C-H4 (85--102) have been studied by using the techniques of thermal denaturation and solubility behaviour. Complexes in 10(-3) M phosphate buffer, 2 - 10(-5) M Na(2)-EDTA, pH 7.0 were prepared by the direct mixing method. For lysine-rich histones (H1 and H2B) it has been found that the main characteristics which governs the interaction with DNA are located in the very lysine-rich part of the molecules, i.e. in the C-H1 and N-H2B segments. These regions are also responsible for a cooperative distribution of the histone along the DNA molecules in the artificial complexes. It appears from our studies that the tertiary structure of the moderately, arginine-rich histone (H2A) is an essential feature for its interaction with DNA. The two arginine-rich histones (H3 and H4) complexed with DNA behave in a similar way, both in thermal denaturation and in DNA precipitation. In the case of C-H4, a marked shift of the melting profile has been observed which is correlated with the presence in the peptide of the hydrophilic cluster Lys-Arg-Gln-Gly-Arg-Thr. Our results suggest that large segments rich in lysine and basic clustering within histones give rise to different modes of electrostatic interaction with DNA.

Animals↗