A physiological importance

How could (3-hydro xy-(3-methylbutyrate be formed in muscle Could it be a physiologically important precursor to cholesterol ... 

Motohashi, H., and Yamamoto, M. Nrf2-Keapl defines a physiologically important stress response mechanism. Trends Mol. Med. 10, 549-557, 2004. 

Pyridoxine phosphate oxidase is a flavoprotein, and activation of the erythrocyte apoenzyme by riboflavin 5 -phosphate in vitro can be used as an index of riboflavin nutritional status (Section 7.4.3). However, even in riboflavin deficiency, there is sufficient residual activity of pyridoxine phosphate oxidase to permit normal metabolism ofvitamin Be (Lakshmi and Bamji, 1974). Pyridoxine phosphate oxidase is inhibited by its product, pyridoxal phosphate, which binds a specific lysine residue in tbe enzyme. In tbe brain, tbe Ki of pyridoxal phosphate is of the order of 2 /xmol per L - the same as the brain concentration of free and loosely bound pyridoxal phosphate, suggesting that this inhibition may be a physiologically important mechanism in the control of tissue pyridoxal phosphate (Choi et al., 1987). 

In vitro experiments (38) showed that iron could form soluble chelates with ascorbic acid at the pH of the normal intestinal lumen. Soluble ascorbic acid-iron chelates formed at an acidic pH remained in solution even after the alkalinization of the medium (39). Intraintestinal installation of the pH-adjusted chelates into the rat enhanced the absorption of iron. The authors also suggest that the ascorbic acid normally present in mammalian bile has a physiologically important role in the absorption of nonheme iron from the diet. Whether the whole ascorbic acid-iron chelate is taken up intact into the mucosal cell under these conditions has not been established. Iron is, at the same time, more soluble, reduced, and more absorbable at intestinal pH in the presence of ascorbic acid those factors, with or without direct mucosal uptake of ascorbic acid-iron complexes, explain the contribution of ascorbic acid to the enhancement of iron availability. 

A physiologically important category of irreversible enzyme inhibition is produced by the antienzymes, exemplified by various trypsin inhibitors. These are proteins that... 

AAT may also be a physiologically important inhibitor of leukocyte neutral protease, kaUikrein, renin, urokinase, plasmin, and thrombin. It probably does not inhibit leukocyte collagenase (a metalloproteinase), as is often stated it more likely inhibits a leukocyte protease that activates procoHagenase. 

A physiologically important aspect of signal transmission via transmembrane receptors is its regulation. The cell has various mechanisms available, with the help of which the number and activity of transmembrane receptors can be regulated. The aim of... 

Most data are available for the pi 10a p85a subtype of PI3-kinase. For brevity, this is referred to as PI3-kinase in the following. The PI3-kinase phosphorylates various Ptdlns derivatives at the 3 position (see Fig. 6.4) in vitro (review Divecha and Irvine, 1995). A physiologically important substrate is PtdIns(4,5)P2, which is converted to PtdIns(3,4,5)P3 by PI3-kinase. PtdIns(3,4,5)P3 is an intracellular messenger that has a regulatory effect in many elementary functions of the cell, such as growth control, chemotaxis and glycogen synthesis (see Section 6.6.2). 

What is the ionization state of phosphoric acid in the cytoplasm Why is phosphoric acid such a physiologically important compound ... 

This chapter presents research on the organization of carotenoid-lipid membranes. Diverse experimental techniques show a pronounced influence of carotenoid pigments on structural and dynamic properties of membranes. It is, however, a matter of debate whether all these effects are physiologically relevant. The problem of a physiological importance of carotenoids in membranes will be pointed out in the last section... 

The efficiency of this four-site adsorption/desorption process can be seen by noting that for a physiologically important change from 5 x 10 M oxygen to 5 x 10 M,... 

---