Time-controlled degradation

First, the effects of aerobic and anaerobic culture conditions on toxaphene degradation were studied with washed P. putida cells grown on camphor and incubated with no readily usable carbon source. The radioactivities remaining in water after extraction with n-hexane were used as an indicator of metabolic activity. This was further extracted with ethyl acetate after acidification to divide this "total polar metabolites" fraction into aqueous buffer phase and ethyl acetate phase, i.e., the total polar metabolites reported refer to summation of the aqueous buffer and ethyl acetate soluble phases (Table 4). All radioactivities have been corrected by zero time controls and autoclaved 8 hr controls are included in each experiment. 

Hydrogel degradation time was controlled by the molecular weight obtained and the crosslink density of the material. 

The degradation rate can be controlled using acidic and basic excipients acidic excipients increase the degradation rates and facilitate a zero-order release rate over a 2-week period (Sparer et al. 1984). Basic additives increase the degradation time of the polymers and create a polymer that degrades specifically at the surface (Heller 1985). By careful choice of the excipient added, the degradation rate can be closely controlled. No experiments have shown the use of these polymers with proteins or peptides. This is not, however, indicative of the fact that these polymers are not compatible with proteins or peptides, but they are probably not the most appropriate polymeric carrier for oral delivery of biomacromolecules. 

Serizawa T, Yamaguchi M, Akashi M (2003) Time-controlled desorption of ultrathin polymer films triggered by enzymatic degradation. Angew Chem Int Ed 42 1115-1118... 

On occasion, positioner use can degrade process control. Such is the case when the process controller, the process, and the process transmitter have time constants that are similar or smaller than that of the positioner/actuator. This situation is characterized by low process-controller P gain (P gain < 0.5), and hunting or limit cycling of the process variable is observed. Improvements here can be made by doing one of the following ... 

Secretion of ecdysone starts the many biochemical processes that are necessary for the molting. The cells in the epidermis are stimulated to produce a new cuticle, and when ready, the insect will creep out of its old skin. The molecular mechanism of ecdysone has been studied in some detail. The molecular target of ecdysone and other ecdysteroids consists of at least two proteins, the ecdysteroid receptor (EcR) and ultraspiracle (USP). Both EcR and USP are members of the steroid hormone receptor superfamily with characteristic ligand-binding domains. An EcR-USP-ecdysteroid complex is formed, which activates several genes that code for transcription factors, i.e., proteins that activate or repress the activity of other genes, and the appropriate amounts of proteases and other enzymes necessary to degrade old structures and rebuild new ones are formed in a time-controlled sequence. 

The breakdown of repeated 2,4-D and MCPA applications made to a field soil has been monitored using a white mustard bioassay procedure (21) Repeated applications of the two herbicides resulted in a reduction in degradation time from 10 weeks for 2,4-D and 20 weeks for MCPA, after one treatment, to 4 and 7 weeks, respectively, after 19 annual applications. From these pretreated soils microbial isolates were extracted and, in mineral salt medium, were found to degrade 2,4-D and MCPA more rapidly than isolates from untreated control soils (35). The microbial isolates from the 2,4-D treatments would also rapidly degrade MCPA added to... 

The prime aim in the alkaline extraction of the demineralized and degraded alga is obviously to obtain maximum extraction in the minimum time without further degradation. A controlling factor is that the extract should contain not more than 0.1% sodium alginate, above which concentration the solution is too viscous to filter. 

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