Enzyme changes with carbon

New data from our experiments on enzyme changes with other chemicals now show that in rats, not only carbon tetrachloride but also ethylene dichloride, benzene, and methanol bring about a reduction in serum B-esterase during 4 days after a single oral dose at the acute level. These findings seem to indicate that the serum esterase activity response is considerably independent of the chemical structure and the molecular configuration of the stressing chemical, except that the stimulation of esterase activity occurs later than with the chlorinated hydrocarbon pesticides. 

This step leaves two cleavage products. The first, derived from the two carbons at the carboxyl end of the fatty acid, is acetyl-CoA, which can be further metabolized in the TCA cycle. The second cleavage product is a shorter fatty acyl-CoA. Thus, for example, the initial step of digesting a fatty acid with 16 carbons is an acyl-CoA molecule where the acyl group has 14 carbons and a molecule of acetyl-CoA. The P-oxidation scheme may be used to accommodate unsaturated fatty acids also. The reactions occur as described previously for the saturated portions of the molecule. Where a trans carbon-carbon double bond occurs between the %- and p-carbons of the acyl-CoA, the accommodation is fairly simple reaction 1 isn t needed. Where the double bonds are in the cis configuration, or are between the P and y carbons, isomerase enzymes change the location of the double bonds to make recognizable substrates for P-oxidation. 

As with carbonic anhydrase the metal is in a cleft that exposes the active site. Interestingly the metal-free enzyme is inactive but the cobalt and nickel analogues are more active. It appears that the transition state complex, where the terminal amino acid side chain is held in place while the peptide bond is hydrolysed, requires six-fold co-ordination. The activation energy required to change from the tetrahedral to octahedral geometries is higher for zinc than the other metals. 

McLean, P., Reid, E., and Gurney, M. W., Effect of azo-dye carcinogenesis on enzymes concerned with urea synthesis in the rat. Biochem. J. 91, 464-473 (1964). McLean, P., and Rossi, F., Changes in the activities of urea-cycle enzymes after the administration of carbon tetrachloride. Biochem. J. 91, 261-270 (1964). McMurray, W. C., Mohyuddin, F., Bayer, S. M., and Rathbun, J. C., Citrul-linuria a disorder of amino acid metabolism associated with mental retardation. Int. Copenhagen Congr. Sci. Study Meat. Retard., Proc. 3rd 1, 117 (1964). McMurray, W. C., Rathbun, J. C., Mohyuddin, F., and Koegler, S. J., Citrul-linuria. Pediatrics 32, 347-357 (1963). 

Most of the microsomal reactions can be classified as oxidations by what are referred to as mixed-function oxidases utilizing molecular oxygen and cofactors. The key enzyme is an iron-hemecytochrome P-450, a flavoprotein dependent in its reduction and reoxidation on the NADPH to NADP reaction. The 450 notation is based on the 450 nm absorption peak the enzyme exhibits on reaction with carbon monoxide. Thus, drug interactions with this enzyme system can be evaluated by measuring absorption spectra changes. 

In addition to nucleic acids, enzymes have also been incorporated into conducting a polymer matrix for biosensor applications. As a transducer, a CP can convert the chemical response into an electric current. To enhance the sensitivity and the response time, fabrication of CPs/enzyme nanocomposites with large surface area is a meaningful objective. Syu and Chang demonstrated the immobilization of urease onto PPy nanotubes over carbon paper substrate by a physical entrapment approach [124]. The composite electrodes exhibited a detection sensitivity for the determination of urea of 53.74 mVdecade and a detection limit on the urea concentration of 1.0 pM. Furthermore, the composite electrode shows rapid response, storage stability and reusability. Lipase can also be covalently immobilized... 

The effect of different amino acids supplements on the synthesis of PHB by recombinant E. coli was evaluated by Mahishi and Rawal. The study revealed that when the basal medium is supplemented with amino acids, except glycine and valine, all other amino acid supplements enhanced PHB accumulation in recombinant E. coli harboring PHB synthesizing genes from S. aureqfaciens. Cysteine, isoleucine, or methionine supplementation increased PHB accumulation by 60, 45, and 61%, respectively. Amino acid biosynthetic enzyme activities in several pathways are repressed by end produa supplementation. End product inhibition in the cysteine biosynthetic pathway controls the carbon flow due to sensitivity of serine transacetylase to cysteine. Hence, supplementation of cysteine favors a change in carbon flux that eliminates the requirement of acetyl-CoA for serine transacetylation which in turn provides more carbon source and acetyl-CoA for PHB synthesis. Degradation of methionine and isoleucine yields succinyl CoA, an intermediate of tricarboxylic acid cycle and allows more acetyl-CoA to enter the PHB biosynthetic pathway. 

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