Enzymes, packing density

Polycondensation reactions in oriented monolayers and bilayers proceed without catalysis, and simply occur due to the high packing density of the reactive groups and their orientation in these layers. Bulk condensation of the a-amino acid esters at higher temperatures does not lead to polypeptides but to 2,5-diketopiperazines. No diketopiperazines are found in polycondensed monolayers or liposomes. Polycondensation in monolayers and liposomes leading to oriented polyamides represents a new route for stabilizing model membranes under mild conditions. In addition, polypeptide vesicles may be cleavable by enzymes in the blood vessels. In this case, they would represent the first example of stable but biodegradable polymeric liposomes. 

Alternatively, an oligomeric polymerase enzyme formed in the cytoplasm precipitates or adsorbs onto the granule surface. At a volume fraction of PHA in the bacterium of approximately 0.58 the latex particles reach a close-packing density and coagulation between latex particles occurs, which is accompanied by a decrease in both the rate of polymerization and molar mass of the polymer formed [41,42,46]. 

Careful examination of the yellowish sediment obtained after spinning down the crude mitochondrial fraction showed it was frequently overlaid with loosely packed, fluffy material —the fluffy layer. Experiments from de Duve s and, later, Novikoff s laboratories in the 1950s demonstrated that the lighter, lysosomal fraction was enriched in a number of hydrolases including acid phosphatase, aryl sulphatase, B glucuronidase, RNAase, and a peptidase, cathepsin. All the enzymes had optimal pHs in the acid range (pH 5-pH 6). Density... 

Fairbaim and Williamson studied P. bracteatum anatomically and compared it to P. somniferum (18). They found the two plants to be very similar in stmcture. The laticifers of P. bracteatum were usually more closely packed and anastomose more frequently. The subcellular fraction of protoplasts from cultured P. bracteatum cells (organelles sedimenting at 1000 g) was the major site where thebaine and sanguinarine accumulated (19). It also contained dopamine as a precursor and the vacuolar enzyme a-mannosidase. Dopamine also appeared in the supernatant. Dopamine compartmentalization in vacuoles of cultured cells was observed by histofluorescence microscopy. Dopamine, sanguinarine, and thebaine occurred in vacuoles of different densities. This result is consistent with... 

Pack AM, Olarte LS, Morrell MJ, et al. Bone mineral density in an outpatient population receiving enzyme-inducing antiepileptic drugs. Epilepsy Behav 2003 4 169-174. 

Parameters defining the quality of the interface such as enzyme orientation, substrate packing, hydrophobicity, charge density, and film pressure come into consideration [2-4], and terms characterizing enzyme activities such as Vmax and Km have different meanings. 

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