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Biomedical subjects

R F Doolittle

Publications and source records attributed to R F Doolittle.

At least 163 records · Page 9Linked to original sources
PubMed1976

Amino acid sequences of lamprey fibrinopeptides A and B and characterizations of the junctions split by lamprey and mammalian thrombins.

The amino acid sequences of the fibrinopeptides A and B from lamprey fibrinogen have been determined. The fibrinopeptide A is the shortest fibrinopeptide ever isolated, being comprised of only six amino acids. The fibrinopeptide B, on the other hand, is the largest fibrinopeptide characterized to date, having 36 amino acid residues and a cluster of covalently bound carbohydrate. As reported previously, lamprey fibrinogen is readily clotted by mammalian thrombins, but only the fibrinopeptide B is released during the process. Lamprey fibrinopeptide A is not released by mammalian thrombins and could only be removed with the use of lamprey thrombin. Firm proof that the lamprey fibrinopeptides A and B are the amino segments of the alpha and beta-chains respectively was obtained by a series of stepwise degradations on lamprey fibrinogen and lamprey fibrins produced in turn by the action of mammalian thrombin (fibrin B) and lamprey thrombin (fibrin A). These studies were supplemented by stepwise degradations on the individual Aalpha and Bbeta-chains. It the case of the lamprey Aalpha-chain it was also possible to release the 6-residue fibrinopeptide A from the isolated chain with lamprey thrombin and demonstrate that the newly exposed amino-terminal sequence begins with the Gly-Pro-Arg sequence characteristic of mammalian fibrin alpha-chains. In fact, the sequences on the fibrin side of both of the junctions split by thrombin(s) are highly conserved and virtually identical with those found in mammalian alpha and beta-chains.

Amino Acid Sequence↗
PubMed1976

Amino acid compositions of the subunit chains of lamprey fibrinogen. Evolutionary significance of some structural anomalies.

Our original objective in studying lamprey fibrinogen was embodied in the notion that the proteins of this ancient vertebrate might themselves by more primitive. As such, it was possible that the subunits of lamprey fibrinogen might have been more similar, one to another, than is the case in higher vertebrates, or even identical. Amino acid analysis of the individual polypeptide chains indicates, however, that the alpha, beta and gamma-chains are instead more dissimilar from each other than are the corresponding chains from human fibrinogen. This finding was somewhat surprising because regions of homology have been detected recently among those three chains when isolated from human fibrinogen, suggesting that all three chains have indeed descended from a common ancestor. The paradox is especially evidenced by the unusual amino acid composition of the lamprey alpha-chain, 45% of which is composed of glycine, serine and threonine. This unusual amino acid distribution may be involved in the anomalous behavior of these chains on sodium dodecyl sulfate polyacrylamide gel electrophoresis.

Amino Acids↗
PubMed1976

The evolution of vertebrate fibrinogen.

The origins of the vertebrate fibrinogen molecule and its constituents chains have been considered, first by examining certain features of the molecule as it exists in a primitive vertebrate (the lamprey), and then by comparing the amino acid sequences of certain portions of the three nonidentical chains as they exist in the human molecule. Although the lamprey protein is distinctly homologous to mammalian fibrinogens, at the present stage of characterization its three nonidentical chains appear to be even more different one from another than are the three mammalian chain types. On the other hand, certain sequence resemblances in the three human chains clearly indicate a common ancestry for the alpha-, beta-, and gamma-chains. It is concluded that the ancient fibrinogen molecule was composed of all identical chains and that its differentiation into three chain types occurred long before the divergence of lampreys and higher vertebrates.

Amino Acid Sequence↗
PubMed1975

Amino acid sequence studies on the alpha chain of human fibrinogen. Location of four plasmin attack points and a covalent cross-linking site.

The amino acid sequence of a 38-residue midsection piece of the alpha chain of human fibrinogen has been determined using a combination of plasmin-derived peptides and cyanogen bromide fragments. The segment contains several important features, including four early plasmin attack points, one of the two alpha-chain cross-linking acceptor sites, and a peptide homologous to one isolated from plasmin digests of bovine fibrinogen, and reported to have anticoagulant activity. The segment is sequentially adjacent to and overlapping with a large molecular weight (20000-25000) fragment released during plasminolysis. This latter material is very rich in glycine and serine and deficient in nonpolar amino acids. It also contains the other alpha-chain cross-linking acceptor site.

Amino Acid Sequence↗
PubMed1975

Amino acid sequence of the carboxy-terminal cyanogen bromide peptide of the human fibrinogen beta-chain: homology with the corresponding gamma-chain peptide and presence in fragment D.

The carboxy-terminal cyanogen bromide fragment of the human fibrinogen beta-chain has been isolated and its structure determined. It is a nonapeptide with the sequence Lys-Ile-Arg-Pro-Phe-Phe-Pro-Gln-Gln and is homologous with a portion of the carboxy-terminal cyanogen bromide fragment of the gamma-chain. The peptide has also been isolated in full yield from cyanogen bromide digests of the plasmin-derived fragment D, indicating that the carboxy-terminal region of the beta-chain is resistant to plasmin digestion. In contrast, a small portion of the corresponding gamma-chain carboxy-terminal region was missing in the same fragment D.

Amino Acid Sequence↗
PubMed1975

Amino acid sequence studies on plasmin-derived fragments of human fibrinogen: amino-terminal sequences of intermediate and terminal fragments.

The progressive changes in amino-terminal sequence brought about by the digestion of human fibrinogen by plasmin have been studied. In addition, the limit products (fragments D and E) have been isolated and characterized in the same way. These studies have confirmed the generally accepted scheme of fibrinogen being changed into a large molecular weight fragment X, which in turn is converted into an intermediate fragment Y and a limit fragment D, followed by the breakdown of fragment Y into an additional fragment D and another core fragment E. Our data allow the precise identification of several of the junctions being attacked, including one in a region of the gamma-chain whose sequence has not previously been reported. The cleavages are not singular in any case, however, and, as suggested by others, intermediate species exist which correspond to "early D," "late D," etc. In addition to localizing the exact bonds split by plasmin, we have been able to sequentially position the core fragments relative to each other, since the gamma-chain amino terminus of fragment D has been found to be contiguous to the known carboxy-terminal sequence of fragment E.

Amino Acid Sequence↗
PubMed1974

Platelet and plasma fibrinogens are identical gene products.

Human platelet fibrinogen has been shown to be indistinguishable from plasma fibrinogen by a variety of criteria, including subunit composition and cross-linking characteristics as judged by sodium dodecyl sulfate-gel electro phoresis, quantitative amino terminal analysis of fibrin, and the amino acid compositions of fibrinopeptides released from platelet and plasma fibrinogens is products of the same gene or genes.

Amino Acid Sequence↗