Enzyme mapping studies

Example 2 Enzyme Mapping Studies by Use of P450 Isozyme Selective Inhibitors... 

The chemical properties of the platinated DNA, termed M13-12A-Pt(-)-Stu I, were investigated by enzymatic, digestion and gel electrophoresis experiments. Platinum completely inhibits cleavage of the DNA by Stu I, as expected from the earlier restriction enzyme mapping studies. In addition, the cis-[Pt(NH3)2 d(pGpG) ] and cA-[Pt(NH3)2 d(pApG) ] intrastrand crosslinks were... 

Pharmacophoric patterns have been proposed as the result of structure-activity studies, modeling studies, mechanistic studies, and enzyme structural studies. While two atom ("distance") and three atom ("triangle") pharmacophoric patterns have been proposed, we would not expect these to be as discriminating as more detailed patterns. Proposed pharmacophoric patterns have been reviewed by Kler,9 Korolkovas,10 and Gund.7 Some additional proposed patterns of drug pharmacophores and of complementary receptor maps are listed in Table I. 

For an experimental study of the S -subsite accessibility, S mapping studies (cf. Sect. 12.5.3.3.4) are suitable. By their specific S -binding capacity, peptide nucleophiles should be capable of pushing aside the acyl moiety from the S region more efficiently than water. Therefore, the aminolysis of acyl enzymes bearing the acyl moiety in S should proceed at higher rates compared with their hydrolysis. Indeed, from the mapping studies it follows that the p-values for the deacylation of Bz-D-Ala-trypsin are dramatically lower than for Bz-L-Ala-trypsin. Consequently, the experimental data of aminolysis also support this unique catalysis mechanism for substrate mimetics. 

The piecewise linear map defined by eqns (4.5) thus allows us to explain the transitions between different simple or complex patterns of bursting as a function of the variation of parameters whose significance can be related to the properties of the biochemical model from which the map originates. Parameter a, for example, is linked to the quantity of substrate consumed by the production of a peak of product P,. An increase in the maximum rate of the reaction catalysed by enzyme Ej should therefore correspond to an increase in parameter a of the piece-wise linear map. Likewise, a rise in the rate constant results in a decrease in the amount of product Pj within the system enzyme Ej, activated by P2, should therefore become less active as increases. The amount of Pj, the substrate for enzyme Ej, will then tend to increase, owing to its diminished consumption in the second enzyme reaction. As enzyme Ei is activated by Pj, the increased level of this product raises the rate of enzyme Ei, which results in an increased amount of substrate consumed during synthesis of a peak of Pj. Thus we can see how an increase in the rate constant k in the enzyme model can also be associated with a larger value of parameter a in the one-dimensional map studied for bursting. 

After release there must be some way of terminating the action of a NT necessitating the presence of an appropriate enzyme and/or uptake mechanism. Such uptake processes can be quite specific chemically. Thus a high-affinity uptake (activated by low concentrations) can be found for glycine in the cord where it is believed to be a NT, but not in the cortex where is has no such action. This specific uptake can be utilised to map terminals for a particular NT, especially if it can be labelled, and also for loading nerves with labelled NT for release studies. 

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