Apical amino

The complex shifts to high-spin on protonation of the apical amino groups. The structure of [Fe(NH3)2sar](N03)4.H20 is a trigonally distorted octahedral (0=29°). Unfortunately, because of the easy oxidation of the NH-CH2 functions to imines, this compound is very air-sensitive, making the spectroscopic characterization rather difficult. 

The relatively low nucleophilicity of the apical amino substituent in cobalt(III) diaminosarcophaginate has been used in acylation and alkylation reactions leading to a variety of apical functionalized cobalt(III) sarcophaginates with apical pendant aromatic and heteroaromatic substituents [109],... 

The reactivity of apical amino groups has been used in the synthesis of surface-active sarcophaginates (surfactants) [110] ... 

Stepwise methylation of apical amino substituents in cobalt(III) sarcophaginate make it possible to obtained a tris-N-methylated complex with conformational inversions in the ethylenediamine moieties from mainly a ZeZ -conformation in [Co(diAMsar)] + cation to an 063 conformation in [Co(diMe3AMHsar)]3+ sarcophaginate both in the solid state and in solution [116]. 

The X-ray crystallography and EPR data, as well as pKa measurements, allow one to propose a structure in which the apical amino groups are protonated and the two coordinated amine sites are deprotonated [244]. The observed rhombic distortion results from structural disorder due to the presence of deprotonated groups in the framework. 

Redox potentials (mV) of the cobalt(III) sarcophaginates with apical amino substituents [116]. 

A good agreement between the Oi values and Hammet s constants is observed in some cases (Fig. 56). For sepulchrate and sarcophaginate cobalt(III)/cobalt(II) pairs with apical amino, methyl, and chlorine substituents, the Log/en values correlate with inductive constants of these substituents (Fig. 56). 

The assumed transition state for this reaction is shown in Scheme 5.5. The two bulky t-butoxy groups are expected to locate at the two apical positions. One of the 3,3 -phenyl groups would effectively shield one face of an imine, and consequently, a diene attacks from the opposite side. Judging from this model, similar selectivities were expected in the Mannich-type reactions of imines with silyl eno-lates. Actually, when ligand 10 was used in the reaction of imine la with S-ethyl-thio-l-trimethylsiloxyethene, the corresponding / -amino thioester was obtained in 84% ee (Scheme 5.6). As expected, the sense of the chiral induction in this case was the reverse of that observed when using catalyst 6 [12, 25]. 

Biochemical studies of plasma membrane Na /H exchangers have been directed at two major goals (1) identification of amino acids that are involved in the transport mechanism and (2) identification and characterization of the transport pro-tein(s). To date, most studies have been performed on the amiloride-resistant form of Na /H" exchanger that is present in apical or brush border membrane vesicles from mammalian kidney, probably because of the relative abundance of transport activity in this starting material. However, some studies have also been performed on the amiloride-sensitive isoform present in non-epithelial cells. 

Recently, Tse et al. [73] and Orlowski et al. [74] have cloned a third isoform of Na /H exchanger (named NHE-3). The inferred 832-amino acid sequence of rabbit NHE-3 is 41% identical with NHE-1, 44% identical with NHE-2, and has a similar secondary structure. In contrast to NHE-1 and NHE-2, NHE-3 is only expressed in epithelia in intestine and kidney. Moreover, administration of glucocorticoids, which stimulates transport activity of the apical Na /H" exchanger in rabbit intestine, increased levels of NHE-3 transcripts but did not affect NHE-1 or NHE-2 [75]. Taken together, these results suggest that NHE-3 may encode a resistant-type Na /H exchanger of epithelia. A fourth Na /H exchanger isoform (NHE-4) is preferentially expressed in stomach [74]. 

We have previously shown that a 209 amino acid region (aa288-497, asymmetric localization domain) of Insc is necessary and sufficient for apical cortical localization and for mitotic spindle orientation along the apical-basal axis (Tio et al 1999). In a yeast two-hybrid screen we identified Partner of Inscuteable (Pins), a novel 658aa protein with multiple repeats of the Tetratricopeptide (TPR) motif. Affinity purification experiments using embryonic extracts demonstrate that Pins complexes with Insc in vivo. In vitro protein interaction assays demonstrates that Pins interacts with the Insc asymmetric localization domain (see Yu et al 2000). 

Na+-amino acid contransporter Apical [108] Basolateral [260] Apical [147]... 

Leier I, Hummel-Eisenbeiss J, Cui Y, Keppler D. ATP-dependent para-amino-hippurate transport by apical multidrug resistance protein MRP2. Kidney Int 2000 57(4) 1636—1642. 

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