Enzyme degradation, control

Hence, sometimes phenomena associated with enzyme kinetics control the rate of biotransformations. If suitable enzymes are present in the microbial community, for example due to consumption of structurally related growth substrates, then we may see immediate degradation of compounds of interest like BQ when they are added to these metabolically competent microbial communities (Fig. 17.17). For such cases, if the abundance of the bacteria is varied, the rate of removal changes accordingly. Consequently, the removal of BQ could be described by a second-order rate law (Smith et al., 1978) ... 

The dietary triacylglycerol, cholesteryl esters, and phospholipids are enzymically degraded ("digested") by pancreatic enzymes, whose secretion is hormonally controlled. 

The rate of cholesterol biosynthesis appears to be regulated primarily by the activity of HMG-CoA reductase. This key enzyme is controlled by the rate of enzyme synthesis and degradation and by phosphorylation-dephosphorylation reactions. Synthesis of the mRNA for the reductase is inhibited by cholesterol delivered to cells by means of low-density lipoproteins (LDLs). 

Factors affecting the rate of synthesis include the level of induction or repression of the gene encoding the enzyme (see Topics G3 and G4 and also the rate of degradation of the mRNA produced from that gene. Many key enzymes at control points in metabolic pathways have particularly short-lived mRNAs and the rate of enzyme synthesis is thus readily controlled by factors that affect the rate of gene transcription. 

Know the heme degradation pathway leading to bilirubin intermediates (recognize structures), enzymes, and controls. 

The other system controlling cholesterol biosynthesis involves both the cytosolic HMG-CoA synthase and the ER enzyme HMG-CoA reductase and is based on the cellular levels of respective mRNAs. Increasing free cholesterol decreases both enzyme activities by decreasing the levels of their mRNAs and increasing enzyme degradation processes. The half-life of HMG-CoA reductase may be as short as 1.7 h. Cellular uptake of LDL maintains cholesterol biosynthesis at a relatively low level, and this is achieved through an LDL degradation product-free cholesterol. Some authorities have maintained that hydroxylated... 

Alternatively, the enzyme in the gut can be utilized to control the release of the active drug in the gut. For example, sulfasalazine, which is employed in the treatment of ulcerative colitis, is a combination of sul-fapyridine and 5-aminosalicylate chemically linked via an azo bond. It remains absorbed and intact throughout the GI tract until it reaches the large intestine, where bacterial azoreductase enzymes degrade the azo bond and release sulfapyridine and 5-aminosalicylate to act locally on the lesions. 

Kim (94) has demonstrated the degradation of myofibrillar proteins purified from porcine semimembranosus muscle by porcine leukocyte lysosomal proteinases. Troponin treated with leukocyte lysosomal pro-teinases mixed with tropomyosin did not result in the normal increase in viscosity of this system. The emulsifying capacity of aetomyosin treated with lysosomal proteinases at 37 °C and pH 7 for 12 hr was higher than that of aetomyosin incubated without enzymes. On the other hand, aetomyosin treated with papain had low emulsifying capacity because of extensive degradation. Control aetomyosin incubated at 37 °C, pH 7 for 12 hr formed a gel after removal of KC1, but aetomyosin treated with lysosomal proteinases or papain did not gel. 

Uses Rheology control agent, flow aid, thickener for latex paints Features Resist, to cellulolytic enzyme degradation Regulatory FDA 21 CFR 175.105,175.300,176.170,176.180,177.1210, 182.99 ERA 40CFR 180.1001 (c) DOT nonregulated SARA 302/304/... 

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