Turnover rates, cellular

When older proteins are broken down in the body, they must be replaced. This concept is called protein turnover, and different types of proteins have very different turnover rates. Protein synthesis occurs during the process of translation on ribosomes. Protein breakdown occurs generally in two cellular locations ... 

Stop protein translation sites. Furthermore, protein synthesis and stability may also be regulated by constantly changing cellular processes and extracellular signals such as heat shock proteins, growth factors, and toxins. The end result of these processes could lead to changes in protein localization and interactions, generation of protein fragments, and alteration in protein function and turnover rates. 

Buccal tissue is a robust tissue owing to its continuous exposure to a multitude of substances and its high cellular turnover rate.92 93 The absence of Langerhans cells in the oral mucosal tissues reduces sensitivity to potential allergens.94,95 Hence irritation and hypersensitivity reactions due to drugs and their formulation excipients may be minimal in the short term as well as chronic treatment by this route. 

The turnover rates of GSH and the activity of GSH synthetase during oxidative stress induced by butylhydroperoxide in young and mature animals have been measured. These studies have found that defense mechanisms against oxidative stress in the brain differ with age. Young people can increase the cellular availability of GSH, whereas older people can increase GSH synthetase activity during oxidative stress. These differences make older people more susceptible to brain oxidative damage. 

Hochachka, P.W. and G.B. McClelland (1997). Cellular metabolic homeostasis during large scale changes in ATP turnover rates in muscles. J. Exp. Biol. 200 381-386. 

The proteins and other molecules that bind to the inositol lipids will affect their turnover rate and the extent of their impact on cellular metabolism. If so many cytoskeletal proteins bind to the inositol lipids, does this mean that the lipids are associated with the cytoskeleton Ptdlns 3-kinase activity is cytoskeletal associated (Dove et al., 1994) and at least one form of Ptdlns 4-kinase, (the type III Ptdlns 4-kinase) is cytoskeletal associated (Stevenson etal., 1998). 

Assimilation of NOs" assimilation of NOs requires the synthesis of NOs and N02 reductases, associated active transport systems, and the turnover of cellular ATP and NADPH (Chapter 32 by Berges and Mulholland, this volume McCarthy, 1981 Syrett, 1981). Further, supply of NOs is limited by rates of nitrification and vertical... 

In contrast to the rapid changes upon receptor activation in intracellular concentrations of lower inositol polyphosphates (e.g., Ins(l,4,5)P3), InsPe concentrations seem immutable. This finding, along with observations of the sluggish incorporation of radiolabeled inositol into InsPe, prompted interpretations of slow turnover rates for InsPe in vivo. However, the identification of InsPe as a precursor to even more phosphorylated inositol polyphosphates overturned these misconceptions and revealed the true dynamic nature of cellular InsPe. 

Many cellular components are in a dyTiemic state whereby they are synthesized and degraded at a constant turnover rate while their total concentration remains constant. The turnover rate can be measured if the specific component can be labeled. 

M (increases in nasal cell Wilmer et al. 1987 turnover rates squamous metaplasia with cellular hyperplasia)... 

M (increased cell turnover rates thinning disarrangement of the nasal epithelium squamous metaplasia with cellular hyperplasia minimal to moderate rhinitis)... 

This increased conversion of pyruvate to lactate decreases the pH in areas of the brain that have rapid ATP turnover rates and leads to cellular destruction. 

II. CELLULAR ENERGY STORES AND METABOLIC TURNOVER RATE... 

Most cellular functions depend on enzymatic reactions. Turnover rates for intracellular enzymes are typically several hundred reactions per second, although the variation in catalytic power is high (Table 4.10). A typical intracellular compartment (L 1 fim) will be well mixed by diffusion if D 10 cm /s, with a diffusion time of 10 ms. In this micrometer-scale compartment, any two molecules will collide every 1 s [131]. Clearly, this rate of collision will have important implications for the overall rate of reaction for enzymes with high turnover number. 

---