Secondary structure relation with molecular weight

Larger molecules such as proteins usually do not fit these predictions, probably because the molecules adopt an ordered three-dimensional structure in which many of the hydrophobic residues are buried within the structure and unavailable for interaction with the reversed phase. As might be expected from the proposed mechanism of separation, the retention of proteins on reversed-phase columns is not related to molecular weight of the sample, but rather the surface polarity of the molecule. Table I shows that there is a correlation of hydrophobicity (measured by mole % of strongly hydrophobic residues) with retention order for seven different proteins. It is unlikely that the retention of all proteins on a reversed-phase column can be correlated in this manner, because many protein structures have few nonpolar residues exposed to the aqueous environment. For example, although the major A and C apolipoproteins are eluted from a ju-Bondapak alkylphenyl column in an order which can be related to the proposed secondary structures, there is little correlation with the content of hydrophobic residues in each protein and the degree of interaction with the stationary phase. A similar lack of correlation be-... 

The essential distinction between the approaches used to formulate and evaluate proteins, compared with conventional low molecular weight drugs, lies in the need to maintain several levels of protein structure and the unique chemical and physical properties that these higher-order structures convey. Proteins are condensation polymers of amino acids, joined by peptide bonds. The levels of protein architecture are typically described in terms of the four orders of structure [23,24] depicted in Fig. 2. The primary structure refers to the sequence of amino acids and the location of any disulfide bonds. Secondary structure is derived from the steric relations of amino acid residues that are close to one another. The alpha-helix and beta-pleated sheet are examples of periodic secondary structure. Tertiary... 

When Herman Mark first evaluated the crystal structure of rubber (with E. A. Hauser) and cellulose (with J. R. Katz) in 1924 and 1925, it was generally accepted that these materials were low molecular weight or monomeric. The unusual properties of these substances, now known to be related to high molecular weight, were then attributed to aggolomeration or "association" of the low molecular weight precursors. A common explanation for the associations were secondary forces such as Johannes Thiele s partial valences. 

Polyethylene is a man-made homopolymer. Its chemical synthesis is well understood. It is a random walk polymer with little secondary or tertiary structure. A batch can largely be characterised by its molecular weight distribution, and its rheology can be related to these parameters by developed rules of polymer behaviour. The action of specific chemicals as plasticisers can be used to modulate these bulk properties in a predictable way, allowing the nature and characterisation of its glass to fluid transition to be predicted. 

Ferritin consists of (1) an apoferritin protein coat, (2) an iron-protein interface, and (3) an inner iron core [7]. The apoferritin coat, or shell, contains 24 subunits arranged as an icosahedron with a molecular weight (MW) of 440 kDa. The subunits are of two related types, designated as H and L, with MW of 21000 and 19000, respectively. These homologous subunits have similar secondary and tertiary structures with a 55% identity and can polymerize together in different proportions to form many hybrid molecules, or isoferritins. 

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