Transmembranal transport mechanism

For each description below, select the transmembranal transport mechanism it best defines ... 

It is clear that macromolecule-drug conjugates or, more accurately, macromolecular prodrugs may well alter the pharmacological and immunological activity of the parent compound. The macromolecular transport vector may vary considerably in size, electrical charges, hydrophobicity and hydrophilicity, and its ability to act as a substrate for transmembrane transport mechanisms. 

Urry, D. W. On the Molecular Structure and Ion Transport Mechanism of the Gramicidin Transmembrane Channel. In Membranes and Transport, Vol. 2, (ed. Martonosi, A.), p. 285, Plenum Publishing Corporation, New York 1982... 

Satisfaction of kinetic order. Carriers follow Michaelis-Menten-type saturation kinetics or first-order kinetics. Ion channels follow the type of respective structure—unimolecular transmembrane channels and bimolecular half-channels follow first- and second-order kinetics, respectively. The kinetic order of supramolecular channels depends on the assembly number. However, this principle can be applied only when the association constants are small. If the association becomes strong, the kinetic order decreases down to zero. Then the validity becomes dubious in view of the absolute criterion of the mechanism. Decreased activation energy compared to the carrier transport mechanism and competitive inhibition by added other cations stand as criteria. 

Two other types of specialized transport mechanisms, pinocytosis and phagocytosis, may also account for the transmembrane movement of some macromolecules (2). In these complex processes, the cell engulfs a droplet of extracellular fluid or a particle of solid material such as a bacterium. The droplet or particle is completely surrounded by a portion of the cell membrane and the resulting vesicle becomes detached and moves into the cell cytoplasm. 

Carafoli, E., and Brini, M., 2000, Calcium pumps structural basis for and mechanism of calcium transmembrane transport. Curr Opin Chem Biol, 4 152-61. 

Had it not been for the remarkable increase in their numbers when the cells are made genetically transformable and the sensitivity of the fluorescence assay with NPN, it is likely they would have remained undetected for many years to come (Figure 24A). It was the striking correlation between PHB/polyP concentrations and transformation efficiencies in A. vinelandii, B. subtilis, and E. colt that led Reusch et al 22,23,25 to postulate that the complexes play a role in DNA transmembrane transport (Figure 24B). Here we will briefly consider the experimental and structural evidence in support of this hypothesis, and speculate on a mechanism by which PHB/polyP may be used for DNA transmembrane transport. 

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