Binding of porphyrin to human serum albumin. Structure-activity relationships

S. Cohen, R. Margalit

Research output: Contribution to journalArticlepeer-review

62 Scopus citations

Abstract

The equilibrium binding of hydroxyethyl vinyl deuteroporphyrin (HVD) and of irreversible porphyrin aggregates to human serum albumin was studied at the molecular level. This protein may function as an endogenous drug carrier for porphyrins in photodynamic therapy of tumours. HVD-protein binding studies revealed two types of binding sites, which are attributed to the two HVD isomers. The binding constant for the high-affinity isomer, 2.1 (±0.3) x 108 M-1, is similar to that previously determined for protoporphyrin. At the same time the binding constant for the lower-affinity HVD isomer, 1.8(±0.3) x 106 M-1, is similar to that previously determined for haematoporphyrin. Irreversible porphyrin aggregates were purified from the haematoporphyrin derivative and from Photofrin and are defined by spectral and chromatographic data. Gel-exclusion studies indicate that the dominant size of these aggregates is ten porphyrin monomeric units. The protein-binding constant of these aggregates is 1.7(±0.2) x 105 M-1, with four binding sites per protein molecule. The distinction between the HVD isomers along the porphyrin-protein affinity sequence gives insight into the relationship of porphyrin structure to porphyrin-albumin binding. On the basis of this study an evaluation of human serum albumin as an endogenous carrier for porphyrins (at various aggregation states) in photodynamic therapy of tumours is presented.

Original languageEnglish
Pages (from-to)325-330
Number of pages6
JournalBiochemical Journal
Volume270
Issue number2
DOIs
StatePublished - 1 Jan 1990
Externally publishedYes

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