The subunit structure of thyroglobulin.

Human and rat thyroglobulin were reduced and alkylated in aqueous alkaline conditions in the absence of denaturants; the product of reduction in both cases has been found to have mol.wt. about 165000, or one-quarter that of the native molecule.     

The primary structure of myohemerythrin.

The complete amino acid sequence of muscle hemerythrin (myohemerythrin) from the sipunculid Themiste (syn. Dendrostomum) pyroides has been determined by analysis of tryptic, chymotryptic, and cyanogen bromide peptides. The primary structure of myohemerythrin differs substantially from that of coelomic hemerythrins of Phascolopsis (syn. Golfingia) gouldii and Themiste pyroides, the amino acid sequence of the muscle protein being only 46 and 45% homologous with the respective coelomic hemerythrins. The most extensive regions of homology between muscle and coelomic proteins occur near the terminii. These and other shorter regions of homology are interpreted in terms of the essential iron ligand residues of the active center.     

The genetic structure of finland.

The Finnish gene pool derives primarily from a relatively homogeneous Finno-Ugric population established during the Iron Age (100 B.C.-800 A.D.) in the southwest and southeast of Finland. Gene flow from Sweden to the southwest coastal areas, dating from prehistoric times, as well as the patterns of settlement and migration throughout Finland during the past 1000 years, appear to have been the major biosocial factors underlying the genetic structure of the contemporary population. Analysis of genetic variation and covariation at nine polymorphic loci in a large random sample of rural Finns, partitioned into either 8 countries or 27 geographic districts, showed that all of the essential features of the genetic structure suggested by the archaeological and historical data could be distinguished. Procedures for obtaining inference on the genetic structure of such a population are reviewed, including coefficients of similarity and (genetic) distance among subpopulations, the relation between linear or planar geographic structure and genetic covariation, and the methods for describing allelic differentiation. Bias resulting from the inappropriate assumption of a simple phylogenetic model can be substantial, expecially for the analysis of isolation by distance; procedures for avoiding misleading inference on the genetic structure are demonstrated.     

The structure of gastrointestinal hormones.

The primary and secondary structure of the three kinds of gastrointestinal hormones, i.e. gastrin, cholecystokinin-pancreozymin and secretin are discussed.     

Primary structure of human alpha 2-macroglobulin. V. The complete structure

The primary structure of the tetrameric plasma glycoprotein human alpha 2-macroglobulin has been determined. The identical subunits contain 1451 amino acid residues. Glucosamine-based oligosaccharide groups are attached to asparagine residues 32, 47, 224, 373, 387, 846, 968, and 1401. Eleven intrachain disulfide bridges have been placed (Cys25-Cys63, Cys228-Cys276, Cys246-Cys264, Cys255-Cys408, Cys572-Cys748, Cys619-Cys666, Cys798-Cys826, Cys824-Cys860, Cys898-Cys1298, Cys1056-Cys1104, and Cys1329-Cys1444). Cys-447 probably forms an interchain bridge with Cys-447 from another subunit. The beta-SH group of Cys-949 is thiol esterified to the gamma-carbonyl group of Glx-952, thus forming an activatable reactive site which can mediate covalent binding of nucleophiles. A putative transglutaminase cross-linking site is constituted by Gln-670 and Gln-671. The primary sites of proteolytic cleavage in the activation cleavage area (the "bait" region) are located in the sequence: -Arg681-Val-Gly-Phe-Tyr-Glu-. The molecular weight of the unmodified alpha 2-macroglobulin subunit is 160,837 and approximately 179,000, including the carbohydrate groups. The presence of possible internal homologies within the alpha 2-macroglobulin subunit is discussed. A comparison of stretches of sequences from alpha 2-macroglobulin with partial sequence data for complement components C3 and C4 indicates that these proteins are evolutionary related. The properties of alpha 2-macroglobulin are discussed within the context of proteolytically regulated systems with particular reference to the complement components C3 and C4.     

The structure of Tetrahymena pyriformis mitochondrial DNA. II. The complex structure of strain GL mitochondrial DNA.

1. Isolated mtDNA from Tetrahymena pyriformis strain GL is a linear duplex molecule with an average molecular weight of 32.6 - 10(6) and without internal gaps or breaks. Denaturation of this DNA results in single strands with a duplex hairpin at one end. The length of this hairpin varies between 0 and 5 micrometer within one preparation. 2. Uder renaturation conditions the single strands with hairpins are able to circularize in two ways, depending on the length of the hairpin. Circularization is also observed after partial digestion with exonuclease III of native strain GL mtDNA. 3. All these data fit a model (see Fig.2) in which the DNA is heterogeneous in length at both ends. At the left end a 10-micrometer duplication-inversion is present; part of this duplication-inversion is complementary to a region at the right end of the molecule. 4. The analogy between the structural peculiarities of strain GL mtDNA and of some linear viral DNAs is stressed.     

The effects of deoxyribonucleic acid secondary structure on tertiary structure.

The secondary structure of supercoiled DNA was varied by changes in ionic strength. For I = 0.075-0.4 the structure remained in the previously established branched form with only minor alterations in molecular dimensions. In 4M-NaCl, which induces linear DNA to change its secondary structure to the C structure and brings about an increase in the superhelix density of the molecule, no extra branches were observed on the molecules. The limiting factors that dictate supercoil structure seem to be the number and position of potential branch points and the proximity with which the two intertwining DNA strands can approach each other on the arms of the branches. This value is close to 10nm under the conditions described, and is 14-15nm at I = 0.2. It is suggested that such values should be borne in mind when models of chromosome structure are being constructed.     

The structure of melittin in membranes.

The conformation of the polypeptide melittin in lipid membranes as determined by Raman spectroscopy is a bent alpha-helix formed by the mainly hydrophobic residues 1-21, and a nonhelical COOH-terminal segment of the hydrophilic residues 22-26. Fluorescence quenching experiments on residue Trp19 reveal that all COOH-termini are located on that side of a vesicular membrane to which melittin was added. By means of fluorescence energy transfer between unmodified and modified Trp19 residues, melittin is shown to aggregate in membranes predominantly in the form of tetramers. These and previous results on the location and orientation of melittin permit the development of a model for the structure of melittin tetramers in membranes. The hydrophilic sides of four bilayer-spanning helices face each other to form a hydrophilic pore through the membrane.