Biological properties, reducibility

The saturated soils that occur during wetland, or lowland, rice cultivation give rise to a set of physical, chemical, and biological properties that are quite different from upland soils. Rice is the only major row crop produced under flooded-soil conditions and the absence of air-filled pores along with reduced soil-atmosphere interactions result in an almost entirely different set of processes than those occurring in upland cropping systems. 

The bis-disulfide bridged human insulin 59 (l.Omg, 0.17pmol) in TFA (0.6mL) was treated with Me-SiCl3 (5 pL 250 equiv) in the presence of PhS(0)Ph (0.7 mg, 20 equiv) at 25 °C for 15 min. NH4F (3 mg) was added to the mixture, and the solvent was removed in under reduced pressure. The residue was dissolved in 50% AcOH (1 mL) and the soln was gel-filtered on Sephadex G-25. The product 42 was further purified by semipreparative HPLC yield 0.6mg (61%) the synthetic human insulin was characterized by amino acid analysis and FAB-MS, it exhibited identical chromatographic and biological properties as a reference compound. 

The need to limit the number of parameters becomes especially evident if molecular shape, which decisively influences the biological properties of chemical compounds, must be considered. Principally, shape can be precisely accounted for by the coordinates of all the atoms in the molecule. Even with rather small molecules (e.g. 20 atoms) one would need a prohibitive amount of parameters (e.g. 60) alone for representation of steric properties. Again, simplifying assumptions are made to reduce the number of parameters. Thus, one can for example assume that only the steric bulk in a certain position determines the biological properties, in which case a one-parameter representation may suffice, e.g. MR or van der Waals volume of the respective substituent. 

Deoxyfructoserotonin has a strong reducing power and ability for complexation. The sugar derivative shows the following biological properties ... 

The different biological properties of NO and HNO can be partially explained by the high reduction potential for NO and the slow rate of deprotonation of HNO. However, HNO is a mild reductant (163, 164), and biomolecules such as ferricyt c (170) and SOD (83, 84) are reduced, at least formally, by HNO donors, resulting in formation of free NO. The relevance of these and other reactions that have been observed with purified biomolecules to the complex, heterogeneous environments of cells and tissue can be determined by elucidation of the chemical biology of HNO. This process includes identification of potential reactions, mechanistic determinations, and systematic comparisons of relative reaction rates, particularly for modification of biological targets in relation to consumption pathways. 

On the other hand, under reducing conditions the pentavalent compounds are easily converted into the trivalent ones. This is of importance since the biological properties within this group seem to be associated with the trivalent state. 

A His residue is often found at the active site of enzymes where it functions as a catalyst in acid-base and nucleophilic processes. Substitution of fluorine on His reduces the pKa by about 5 pH units, and this dramatic drop in basicity is reflected in altered biological properties of FHis-containing proteins. The presence of 2-FHis in cell cultures inhibits the stimulation of several enzymes, for example, the stimulation of pineal gland A-acetyltransferase activity, in cell culture and in vivo. This stimulation is accompanied by His and cyclohex-imide-sensitive incorporation of 2-FHis into cellular protein192,193. A direct comparison of His and 2-F-His in mouse L cells showed that the analogue is incorporated at about 17% the efficiency of the parent194.4-FHis showed none of the above biological activity. 

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