Housekeeping functions

All members of OATP/Oatp family contain 12 TM domains. Certain transporters show a more restricted tissue expression pattern (i.e., OATP1B1 [old name OATP-C]/liver), while others such as OATP2B1 (old name OATP-B) can be detected in almost every tissue that has been investigated [22], This indicates that some OATPs/Oatps have organ-specific functions, while others might be involved in housekeeping functions. 

Eaure D (2002) The family-3 glycoside hydrolases from housekeeping functions to host-microbe interactions. Appl Environ Microbiol 68 1485... 

Although it is still difficult to establish clear cause effect relationships, it is widely accepted that chemical pollution contributes for antibiotic resistance dissemination [10, 33, 34]. There are evidences that antibiotic resistance increase is related with environmental pollution and anthropic pressures. In this respect, antibiotics seem to be a major, although not the unique, form of pollution, mainly because it is estimated that about 75% of the antibiotics consumed by humans and animals are eliminated as active substances [35, 36]. In the environment, antibiotics can suffer adsorption, photolysis or biodegradation, reaching very low concentrations [37]. Nevertheless, at sub-inhibitory levels, as they are found in the environment, antibiotics can promote several alterations on housekeeping functions of the cells. Apparently, some of these alterations are not associated with antibiotic resistance. Even though, they contribute for the perturbation of the microbial community, leading, eventually, to an overall resistance increase [1, 34, 38]. 

All plants contain a PEPCase enzyme which, among other likely roles (Vidal et al., 1986), serves to replenish tricarboxylic acid cycle intermediates that are consumed during ammonium assimilation (Latzko Kelly, 1983). The role of this enzyme, other than its presumed housekeeping function, has not been studied in any detail and its activity is probably not controlled by environmental factors. Isoforms of PEPCase have been observed in many plants (C3, C4 and CAM) for example, in rice five isoforms have been detected immunologically and in most plants two to four bands that react with anti-PEPCase antibodies are found (Matsuoka Hata, 1987). It is not clear how these isoforms arise, e.g. by post-translational modification of one form, or whether all of these forms are products of different genes. The housekeeping-type PEPCase enzyme, concerned with anaplerotic functions, is distinct from other PEPCase enzymes that function in plants with C4 and CAM metabolism (see below). 

Two genes encoding different PEPCase enzymes have been identified and characterised in the ice plant (Cushman et al., 1989 Cushman Bohnert, 1989a,b). ppcl is the CAM-specific form, which is expressed predominantly in green tissue, leaves and shoots. A second isogene, ppc2, appears to be responsible for the housekeeping functions of PEPCase and is expressed constitutively at low levels in all tissues of the plant. 

Okunade, G.W., Miller, M.L., Pyne, G.J., Sutliff, R.L., O Connor, K.T., Neumann, J.C., Andringa, A., Miller, D.A., Prasad, V., Doetschman, T., Paul, R.J., Shull, G.E., 2004, Targeted ablation of plasma membrane Ca2+-ATPase (PMCA) 1 and 4 indicates a major housekeeping function for PMCA1 and a critical role in hyperactivated sperm motility and male fertility for PMCA4. J Biol Chem 279, 33742-33750. 

A more orderly type of cell death is apoptosis, in which the cells become encapsulated and are systematically removed from the organ. This essential housekeeping function is accomplished in the liver by special cells called Kupffer cells. These cells perform phagocytosis, in which a solid particle, such as a cell remnant or other foreign matter in the liver, becomes encapsulated in a plasma membrane and incorporated into the Kupffer cell, which is then eliminated. 

Synthesis of molecular chaperones may be constitutive or stress-induced. Several size classes of molecular chaperones are synthesized constitutively to facilitate the housekeeping functions associated with protein synthesis and maturation. All organisms contain constitutively expressed chaperones, and the ubiquitous occurrence of these proteins is strong reason to believe that they appeared very early in evolution. Orthologs of some classes of molecular chaperones are found in prokaryotes and all eukaryotes. 

Cox-1 is constitutively expressed and responsible for most of the housekeeping functions of eicosanoids, including processes such as calcium metabolism in the bone, and stomach mucous membrane maintenance. It is also responsible for synthesis of thromboxanes in thrombocytes and of prostacyclin (PGI) in endothelial cells, which have antagonistic function in thrombocyte aggregation and activation (see later). 

This chapter will discuss cell water, the regulation of cell volume, and the modifications produced by cell pH. These topics are housekeeping functions and do not have the glamour of genetic engineering. Nevertheless, it is quite probable that one of the first requirements for life to evolve was a guarantee of a stable fluid environment. Mechanisms had to be established that would regulate the cell content of water. 

Proteins, just like RNAs (Chapter 25), have a life-time in the cell that is determined by their turnover rate. The half-life of a protein is the period of time it takes to degrade 50% of the protein and represents the stability of a protein As shown in Table 27.1, protein half-lives are different and range from minutes to days. In general, regulatory proteins have short half-lives, such as those involved in metabolic control points, whereas proteins that provide "housekeeping" functions are long lived. 

Inhibition of COX that leads to less proinflammatory PG production at the injury site is the major mechanism of action of nonsteroidal anti-inflammatory drugs (NSAID) (4). Molecular cloning studies have identified two forms of COX (5,6), COX-1, a constitutive form responsible for housekeeping functions, and COX-2, an inducible form that mediates many of the inflammatory and inducible effects. Both forms carry out essentially the same catalytic reaction and have similar primary sequences (5,6). Selective inhibitors of the inducible COX-2 would therefore be ideal as NSAID that are free of side effects (7). 

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