Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Acids”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,225 records · Page 68Linked to original sources
PubMed1986

Isocholic acid formation from 7 alpha,12 alpha-dihydroxy-3-keto-5 beta-cholanoic acid with human liver enzyme.

The formation of isocholic acid from 7 alpha, 12 alpha-dihydroxy-3-keto-5 beta-cholanoic acid by human liver preparations was examined in vitro. Liver preparations were incubated with 7 alpha, 12 alpha-dihydroxy-3-keto-5 beta-cholanoic acid at pH 7.4 in a phosphate buffer containing NADPH or NADH. The products formed were analyzed by gas chromatography and gas chromatography/mass spectrometry. Results showed that 7 alpha,12 alpha-dihydroxy-3-keto-5 beta-cholanoic acid was reduced mainly to isocholic acid and to cholic acid in a smaller amount in the presence of NADPH, while it was reduced only to cholic acid in the presence of NADH. The reducing enzyme participating in the formation of isocholic acid was localized largely in the cytosol and had more specificity to the unconjugated form as substrate than to the conjugated forms. 3-Keto bile acid analogues, 3-keto-5 beta-cholanoic and 7 alpha-hydroxy-3-keto-5 beta-cholanoic acids were not reduced to the corresponding iso-bile acids by the cytosol in the same conditions used in the isocholic acid formation and the activity of the enzyme catalyzing the reduction of 7 alpha,12 alpha-dihydroxy-3-keto-5 beta-cholanoic acid to isocholic acid was not inhibited by the addition of 3-keto-5 beta-cholanoic acid or 7 alpha-hydroxy-3-keto-5 beta-cholanoic acid to the reaction mixture. Furthermore, on column chromatography of Affi-Gel Blue, the peak of the enzyme catalyzing the reduction of 7 alpha,12 alpha-dihydroxy-3-keto-5 beta-cholanoic acid to isocholic acid was clearly distinguished from that of the enzyme catalyzing the reduction of 3-keto-5 beta-cholanoic acid to isolithocholic acid and that of alcohol dehydrogenase. These results indicate that this enzyme catalyzing the reduction of 7 alpha,12 alpha-dihydroxy-3-keto-5 beta-cholanoic acid to isocholic acid is different from the enzyme(s) catalyzing the reduction 3-keto-5 beta-cholanoic and 7 alpha-hydroxy-3-keto-5 beta-cholanoic acids to the corresponding iso-bile acids and from alcohol dehydrogenase, and has a stereospecific character for 7 alpha,12 alpha-dihydroxy-3-keto-5 beta-cholanoic acid.

Bile Acids and Salts↗
PubMed2002

Low and high affinity amino acid H+-cotransporters for cellular import of neutral and charged amino acids.

Amides and acidic amino acids represent the major long distance transport forms of organic nitrogen. Six amino acid permeases (AAPs) from Arabidopsis mediating transport of a wide spectrum of amino acids were isolated. AAPs are distantly related to plasma membrane amino acid transport systems N and A and to vesicular transporters such as VGAT from mammals. A detailed comparison of the properties by electrophysiology after heterologous expression in Xenopus oocytes shows that, although capable of recognizing and transporting a wide spectrum of amino acids, individual AAPs differ with respect to specificity. Apparent substrate affinities are influenced by structure and net charge and vary by three orders of magnitude. AAPs mediate cotransport of neutral amino acids with one proton. Uncharged forms of acidic and basic amino acids are cotransported with one proton. Since all AAPs are differentially expressed, different tissues may be supplied with a different spectrum of amino acids. AAP3 and AAP5 are the only transporters mediating efficient transport of the basic amino acids. In vivo competition shows that the capability to transport basic amino acids in planta might be overruled by excess amides and acidic amino acids in the apoplasm. With the exception of AAP6, AAPs do not recognize aspartate; only AAP6 has an affinity for aspartate in the physiologically relevant range. This property is due to an overall higher affinity of AAP6 for neutral and acidic amino acids. Thus AAP6 may serve a different role either in cooperating with the lower affinity systems to acquire amino acids in the low concentration range, as a system responsible for aspartate transport or as an uptake system from the xylem. In agreement, a yeast mutant deficient in acidic amino acid uptake at low aspartate concentrations was complemented only by AAP6. Taken together, the AAPs transport neutral, acidic and cationic amino acids, including the major transport forms, i.e. glutamine, asparagine and glutamate. Increasing proton concentrations strongly activate transport of amino acids. Thus the actual apoplasmic concentration of amino acids and the pH will determine what is transported in vivo, i.e. major amino acids such as glutamine, asparagine, and glutamate will be mobilized preferentially.

Algorithms↗