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Biomedical subjects

N Lieska

Publications and source records attributed to N Lieska.

25 records · Page 2Linked to original sources
PubMed1980

Subunit characterization of lens intermediate filaments.

The intermediate filaments from the bovine ocular lens can be fractionated into three 54000 dalton polypeptides (alpha, beta and gamma) which are present in equimolar quantities and differ from one another with respect to isoelectric point, two-dimensional peptide map pattern and total amino acid composition. The polypeptides, for which the name lentin is proposed, were purified from the 8 M urea extract of the water-insoluble residue of the cortical fiber cells by ion-exchange chromatography on DE- and CM-cellulose. The regeneration of native-appearance filaments from each purified fraction, or combinations thereof, definitively established the three polypeptides as the subunit species. Additionally, small diameter 'protofilaments' were regenerated when one or two fractions were utilized, but not when all three fractions were combined. This, together with the fact that the stoichiometric yield of the three species was invariably equimolar, suggests that alpha, beta, and gamma may be distinct entities not related by artifactual interconversion.

Amino Acids↗
PubMed1979

Characterization of the myoglobin of the lamprey Petromyzon marinus.

Myoglobin has been identified in the myocardium of the lamprey Petromyzon marinus, one of the most primitive of all vertebrates. This protein was isolated by ammonium sulphate fractionation and purified by successive chromatography on Ultrogel AcA 54, DEAE-Sephadex and CM-23 cellulose. The molecule differs substantially from the monomeric hemoglobins found in the lamprey as evidenced by its elution profile on DEAE-Sephadex and the fingerprint pattern of its enzymically-produced peptides. The functional significance of this protein in Agnatha is discussed.

Amino Acid Sequence↗
PubMed1979

The use of amino acid sequence analysis in assessing evolution.

The thirteen year history of assessing evolution by amino acid sequence analysis has made apparent the limitations imposed upon this system by the finite nature of the characters. This finiteness exists on several levels and ultimately expresses itself as parallelism, back mutation and the retention of primitive characters in the sequences of proteins from present day species and the putative ancestral protein chains. Sequence analysis shares these problems with other molecular approaches, but because it is concerned both with the nucleotide substitutions in the genome and with the functional roles of proteins, it has unique advantages. For example, the large fluctuation in the rate of fixation of mutations in a protein's evolution can be detected and used to point out the unreliability of any molecular clock for estimating divergence dates. Moreover, when consideration is given to studies which assign functional significance to specific amino acid sites in a protein, changes in function during the descent of a protein can be appreciated and their significance correlated with organismal evolution.

Amino Acid Sequence↗
PubMedDate not supplied

Proteins of the intermediate filament cytoskeleton as markers for astrocytes and human astrocytomas.

There is a pressing need for a more accurate system of classifying human astrocytomas, one that is based on morphologic characteristics and that could also make use of distinctive biochemical markers. However, little is known about the phenotypic characteristics of astrocytomas. Recent studies have shown that the expression of proteins comprising the intermediate filament (IF) cytoskeleton of astrocytic cells is developmentally regulated. It is our hypothesis that this changing protein profile can be used as the basis of a system for clearly and objectively classifying astrocytomas. A spectrum of human astrocytomas has been examined by immunofluorescence microscopy employing antibodies to several IF structural subunit proteins (GFAP, vimentin, and keratins) and an IF-associated protein, IFAP-300kDa. These proteins occupy unique temporal niches in the cytogenesis of the astrocytic cells: keratins in cells of the neuroectoderm; vimentin and IFAP-300kDa in radial glia and immature glia; GFAP in mature astrocytes; and vimentin in some mature astrocytes. In agreement with previous reports, our immunofluorescence studies have revealed both GFAP and vimentin in all astrocytoma specimens. Two new observations, however, are of particular interest: IFAP-300kDa is detectable in all astrocytic tumors, and the proportion of keratin-containing cells present in the astrocytomas is in direct relationship to the degree of the malignancy. Because IFAP-300kDa is not present in either normal mature or reactive astrocytes, this protein appears to represent a specific marker of transformed (malignant) astrocytes. If it is presumed that higher malignancy grades represent the most dedifferentiated cellular state of the astrocytes, the presence of keratin-containing cells is not totally unexpected, given the ectodermal (epithelial) origin of the CNS. Specific developmentally regulated proteins of the IF cytoskeleton thus appear to hold great potential as diagnostic markers of astrocytomas and as tools for investigating the biology of these tumors.

Astrocytes↗