Enzymatic cleavage

Other examples illustrating the effect of substituent distribution on properties include (/) enzymatic stabiUty of hydroxyethjlceUulose (16,17) (2) salt compatibihty of carboxymethylceUulose (18,19) and (J) thermal gelation properties of methylceUulose (20). The enzymatic stabUity of hydroxyethylceUulose is an example where the actual position of the substituents within the anhydroglucose units is considered important. Increasing substitution at the C2 position promotes better resistance toward enzymatic cleavage of the polymer chain. Positional distribution is also a factor in the other two examples. 

Chemically Controlled. These systems are classified together because of the hydrolysis or enzymatic cleavage of a chemical bond that allows dehvery of the dmg. There are two main types of systems, ie, pendent chain systems and bioerodible systems. 

In the pendent chain systems, the dmg is chemically bound to a polymer backbone and is released by hydrolytic or enzymatic cleavage of the chemical bond. The dmg may be attached directiy to the polymer or may be linked via a spacer group. The spacer group may be used to affect the rate of dmg release and the hydrophilicity of the system. These systems allow very high dmg loadings (over 80 wt %) (89) which decrease the cost of the polymeric materials used ia the systems. These systems have beea examiaed by many iavestigators (111,112). 

Figure 1S.6 Enzymatic cleavage of immunoglobulin IgG. The enzyme papain splits the molecule in the hinge region, yielding two Fab fragments and one Fc fragment.

Table 11 Prechromatographic denvatization involving hydrolytic and enzymatic cleavage reactions...

The enzymatic cleavage of esters is a vast and extensively reviewed area of chemistry. Recently, several new esters have been examined primarily for the preparation of peptides and glycopeptides. 

In some cases, receptor inactivation, e.g., of the V2 vasopressin receptor, is mediated by agonist-induced enzymatic cleavage of the GPCR. This nonendocytic proteolysis is promoted by a plasma membrane-associated metalloprotease. Proteinase-activated receptors (PARs) such as the thrombin receptor also follow a distinctly different pathway. PARs require the enzymatic cleavage of their N terminus, and the newly generated N terminus activates the receptor. Once... 

The amino acid sequence may be such that enzymatic cleavage at different residues may give rise to identical fragments, thus reducing the number of discrete polypeptides expected. Examination of Table 5.7 shows that, in this case, fragments T7 and T13 are identical. 

Hortensteiner, S., Vicentini, F., and Matile, P., Chlorophyll breakdown in senescent cotyledons of rape, Brassica napus L. enzymatic cleavage of pheophorbide a in vitro, New Phytol, 129, 237, 1995. 

Olson, J.A. and Hayaishi, O., The enzymatic cleavage of beta-carotene into vitamin A by soluble enzymes of rat liver and intestine, Proc. Natl Acad. Sci. USA, 54,1364,1965. 

Goldman P (1965) The enzymatic cleavage of the carbon-fluorine bond in fluoroacetate. J Biol Chem 240 3434-3438. 

La Nauze JM, H Rosenberg, DC Shaw (1970) The enzymatic cleavage of the carbon-phosphorus bond purification and properties of phosphonatase. Biochim Biophys Acta 212 332-350. 

Hapten density, and also the common positions where haptens are bound, can also be estimated by cyanogen bromide or enzymatic cleavage of the protein and either MALDI-MS or separation of the components by reversed-phase ion-pair chromatography and electrospray or electrospray time-of-flight (TOF) analysis. 

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