Linked Life Data

3707952

Source:http://linkedlifedata.com/resource/pubmed/id/3707952

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
2
pubmed:dateCreated
1986-7-2
pubmed:abstractText
The effects of hydrophobicity and charges of dicarboxylic porphyrins upon their interactions with membrane model systems are investigated. Four protonation steps are evidenced from fluorescence emission studies of hematoporphyrin IX and its more hydrophobic parent compound lacking of alcoholic chain, deuteroporphyrin IX. They are attributed to the successive protonations of the inner nitrogens of the porphyrin cycle (pK = 4.7 and 2.9 for hematoporphyrin and 4.4 and 2.7 for deuteroporphyrin) and successive deprotonations of propionic groups (pK approximately equal to 5.0 and 5.5 for hematoporphyrin and 5.4 and 6.0 for deuteroporphyrin). These porphyrins, as well as their dimethyl ester forms, are shown to incorporate as monomers into the hydrophobic bilayer of egg phosphatidylcholine small unilamellar vesicles, although the esterified forms are highly aggregated in aqueous solutions. In the case of the non-esterified forms, the incorporation of the porphyrins into the lipidic bilayer is reversible and strongly pH-dependent. A theoretical model is presented which takes into account the various protonation steps and the partition equilibria of the porphyrin between the vesicle lipidic phase and the water medium. The neutral form of the porphyrin (i.e., carboxylic groups protonated) presents the higher affinity, with constants of K approximately equal to 2 X 10(5) and K approximately equal to 6 X 10(6) M-1 (relative to lipid concentration) for hematoporphyrin and deuteroporphyrin, respectively. Protonation of one inner nitrogen leading to the monocationic form is sufficient to prevent incorporation into the hydrophobic bilayer. On the other hand, deprotonation of the peripheral propionic chains leading to anionic forms is less effective. These interactions between vesicles and porphyrins lead to shifts of the apparent pK of nitrogens and carboxylic groups, the latter one being now in the range of physiological pH. These results are discussed with regards to the hypothesis of a possible role of pH in the preferential uptake of porphyrins by tumors.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
May
pubmed:issn
0006-3002
pubmed:author
pubmed:issnType
Print
pubmed:day
28
pubmed:volume
857
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
238-50
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1986
pubmed:articleTitle
Spectrofluorimetric study of porphyrin incorporation into membrane models--evidence for pH effects.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't