Fractioning in vivo

Some divalent cations such as Cu and Pb form very stable complexes with pectate, but are unlikely to be present at sufiScient concentration in the apoplast of plants to form a major fraction of the counterions associated with the pectic fraction in vivo. The Al ion may deserve closer examination, as it is certainly able to displace Ca from cell walls and reaches substantial concentrations in plant roots under some conditions [60,61]. aluminium is not usually considered to be freely translocated, however. Basic peptides with their negative charges spaced at a similar interval to galacturonans (0.43 nm or a small multiple thereof) can in principle have a very high afiBnity for pectate [62,63], but the extensins that are associated with the most insoluble pectic fractions [M] do not appear to have this type of structure. The possibility that the non-extractable pectic polymers in most cell walls are very strongly complexed with some cation other than Ca " cannot be ruled out, but there is little evidence to support it at present. 

Stupperich, E., Eisinger, H. J., and Albracht, S. P. J., 1990, Evidence for a super-reduced cobamide as the major corrinoid fraction in vivo and a histidine residue as a cobalt ligand of the para-cresolyl cobamide in the acetogenic bacterium Sporomusa-ovata, Eur. J. Biochem. 193 1050109. 

Fia. 1. Time curves for the incorporation of valine-C into the proteins of liver cell fractions in vivo. The valine injected at zero time had a specific activity of 15,300 counts/min/nmole. [Taken from Keller and co-workers (.W). ... 

The most important part of fatty acid synthesis is achieved in vitro in this cell fraction in vivo it occurs in the microsomes. This synthesis is thus extramitochondrial in both cases. Nicotinamides as such cannot difiFiise through the cell membrane (Lehninger, 1951,... 

SCE increases absolute colony number and surviving fraction of CEU-E, CEU-G, and CEU-GM in kradiated human BM. An increase in the fraction of CDSd cells in the radioresistant S-phase has been noted, which suggests a possible mechanism (184). A cautionary note has been sounded about attempting to predict interactions between SCE and CSEs in hemopoieticaHy deprived individuals (185). Although SCE synergizes with GM-CSE or GM-CSE and lL-3 to increase CEU-GM in vitro, no such effect has been found in vivo. 

Arvin [9046-56-4] is a purified fraction from the cmde venom of Agkistrodon rhodostoma (48). The action of this venom fraction is selectively specific for fibrinogen and can rapidly deplete fibrinogen in vivo safely from the ckculating blood. Blood without fibrinogen cannot undergo clot formation. 

In normal human subjects, ANP infusion for one hour causes increased absolute and fractional sodium excretion, urine flow, GFR, and water clearance (53—55). As shown in many in vitro and in vivo animal studies, ANP achieves this by direct effect on the sodium reabsorption in the inner medullary collecting duct, ie, by reducing vasopressin-dependent free-water and sodium reabsorption leading to diuresis and by indirect effect through increased hemodynamic force upon the kidney. ANP inhibits the release of renin and aldosterone resulting in the decreased plasma renin activity and aldosterone concentration (56,57). 

Wong, W.W., Cochran, W.J., Klish, W.J., Smith, E.O.B., Lee, L.S. and Klein, P.D. 1988 In vivo isotope-fractionation factors and the measurement of deuterium- and oxygen-18-dilution spaces from plasma, urine, saliva, respiratory water vapor, and carbon dioxide. American Journal of Clinical Nutrition 47 1-6. 

Recently, water-soluble protein fractions, isolated from extracts of bone matrix, were incorporated into a collagen matrix and shown to induce bone (67,68) and cartilage formation both in vitro and in vivo (69,70). In the latter studies, in the absence of the collajgen delivery system, the proteins were incapable of inducing cartilage formation in vivo when implanted intramuscularly into mice. The success of this approach appears to depend on delivering the active agents at an effective dose over an extended time period. 

Research in this area advanced in the 1970 s as several groups reported the isolation of potent toxins from P. brevis cell cultures (2-7). To date, the structures of at least eight active neurotoxins have been elucidated (PbTx-1 through PbTx-8) (8). Early studies of toxic fractions indicated diverse pathophysiological effects in vivo as well as in a number of nerve and muscle tissue preparations (reviewed in 9-11). The site of action of two major brevetoxins, PbTx-2 and PbTx-3, has been shown to be the voltage-sensitive sodium channel (8,12). These compounds bind to a specific receptor site on the channel complex where they cause persistent activation, increased Na flux, and subsequent depolarization of excitable cells at resting... 

Complex investigations, for example on the (sub)cellular level, can be performed in a fraction of the time required for wet [in vivo or in vitro) studies. 

Clearly, the control of gene expression at the transcriptional level is a key regulatory mechanism controlling carotenogenesis in vivo. However, post-transcriptional regulation of carotenoid biosynthesis enzymes has been found in chromoplasts of the daffodil. The enzymes phytoene synthase (PSY) and phytoene desaturase (PDS) are inactive in the soluble fraction of the plastid, but are active when membrane-bound (Al-Babili et al, 1996 Schledz et al, 1996). The presence of inactive proteins indicates that a post-translational regulation mechanism is present and is linked to the redox state of the membrane-bound electron acceptors. In addition, substrate specificity of the P- and e-lycopene cyclases may control the proportions of the p, P and P, e carotenoids in plants (Cunningham et al, 1996). 

In contrast to previous in vivo models, this in vitro model provides the possibility of dissociating experimentally two important processes of intestinal absorption cellular uptake and secretion. Under conditions mimicking the postprandial state (taurocholate/oleic acid supplementation), differentiated Caco-2 cells were able to (1) take up carotenoids at the apical sides and incorporate them into CMs and (2) secrete them at the basolateral sides associated with CM fractions. Using this approach, the extent of absorption of P-carotene through Caco-2 cell monolayers after 16 hr of incubation was 11.2%, a value falling within the in vivo range (9 to 22%). ° - Of the total amount of P-carotene secreted, 78% was associated with the two CM fractions and 10% with the VLDL fraction. ... 

Bioassay for "killing" ability (in vivo and in vitro against bacteria) of peritonial macrophages after treatment with polysaccharide fractions. 

D. J., Jeffrey, P. Improving the in vitro prediction of in vivo centtal nervous system penetration Integrating permeability, P-glycoprotein efflux, and free fractions in blood and brain. 

Albano, E., Lott, K.A.K., Slater, T.F., Stier, A., Symons, M.C.R.and Tomasi, A. (1982). Spin trapping studies on the free radical products formed by metabolic activation of carbon tetrachloride in rat liver microsomal fractions, isolated hepato-cytes and in vivo in the rat. Biochem. J. 204, 593-603. 

Comporti, M., Saccocci, C. and Dianzani, M.U. (1965). EfiFect of carbon tetrachloride in vitro and in vivo on lipid peroxidation of rat liver homogenates and subcellular fractions. Enzymologja 29, 185-204. 

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