Biological transporters

An important aspect of biological transport is that nature makes extensive use of the reduction of dimensionality to speed up search and discovery (SD) (see also section C2.14.6.2). SD is enonnously enlranced upon moving from tliree to two or one dimensions, because the spatial extent to be explored is drastically reduced. Affinity follows kinetics in being enlranced upon moving from tliree dimensions to two dimensions 1791. 

FIGURE 5.13 Two basic types of biological transport are (a) transport within or between different cells or tissues and (b) transport into or out of cells. Proteins function in both of these phenomena. For example, the protein hemoglobin transports oxygen from the lungs to actively respiring tissues. Transport proteins of the other type are localized in cellular membranes, where they function in the uptake of specific nutrients, such as glucose (shown here) and amino acids, or the export of metabolites and waste products. 

Braun K., Peschke P., Pipkorn R., Lam-pel S., Wachsmuth M., Waldeck W., Friedrich E., Debus J. A biological transporter for the delivery of peptide nucleic acids (PNAs) to the nuclear compartment of living cells./. Mol. Biol. 

True zwitterionic compounds are rare among drugs. The oral absorption of truly zwitterionic compounds is poor unless the compound is a substrate for an absorptive biological transporter as in an a-amino acid which is a substrate for the PepTl nutrient transporter. The aqueous solubility of a true zwitterionic compound will be at a minimum at the isoelectric point which unfortunately for many compounds happens close to the neutral pH at which oral absorphon occurs. Species extrapolation predicting oral absorphon and pk/pD from preclinical animal tests to man are difficult for zwitterions. 

Compounds that are substrates for biological transporters are exceptions to the rule... 

Biological Transport Phenomena in the Gastrointestinal Tract Cellular Mechanisms... 

MH Friedman. Principles and Models of Biological Transport. New York Springer-Verlag, 1986. 

Kam, N.W.S. et al. (2005) Carbon nanotubes as multifunctional biological transporters and near-infrared agents for selective cancer cell destruction. Proceedings of the National Academy of Sciences of the U.S.A., 102 (33), 11600-11605. 

Gruetter, R., Novotny, E. J., Boulware, S. D. etal. Non-inva-sive measurements of the cerebral steady-state glucose concentration and transport in humans by 13C magnetic resonance. In L. Drewes and A. Betz (eds), Frontiers in Cerebral Vascular Biology Transport and its Regulation, vol. 331. New York Plenum Press, 1993, pp. 35-40. 

Time required to transport selected radionuclides added into marine waters at surface from the upper mixed layer by biological transport... 

Govindarajan, S. and V.N.R. Rao. 1992. Accumulation of trace metals in the marine biota and their biological transport. Acta Botan. Indica 20 1-5. 

Table 32.12 Time Required to Transport Selected Radionuclides Added into Marine Waters at Surface out of the Upper Mixed Layer by Biological Transport (Processes include diurnal vertical migration, fecal pellets, and sinking of dead matter.)...

Biological interfaces. 2. Chemical kinetics. 3. Biological transport. I. Leeuwen, H. P. van. II. Koster, Wolfgang. III. Series. 

The biocompatibility and toxicological studies of CNTs have become a controversial hotspot. Although several reports showed that CNTs are non-toxic and could be used as in vivo multifunctional biological transporters (Kam et al., 2005), there is no doubt that the possible hazards associated with CNTs are significant, and that concern is valid the key to address the challenge is to clarify the range and mechanism of nanohazards of CNTs, and possible measurements to reduce CNTs toxicity. 

Rective Sites and Biological Transport Halvor N. Christensen... 

Edwards, J. 0. Proceedings of Symposium on Non Biological Transport and Transformation of Pollutants on land and Water, National Bureau of Standards, 1976. 

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