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Proceedings Paper

Membrane lipid-protein interactions modify the regulatory role of adenosine-deaminase complexing protein: a phase fluorometry study of a malignancy marker
Author(s): Abraham H. Parola; Nurith Porat; Valeria R. Caiolfa; David Gill; Lutz A. Kiesow; Mathew Weisman; S. Nemschitz; Dahlia Yaron; Karen Singer; Ethel Solomon
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Paper Abstract

The role of membrane lipid-protein interactions in malignant cell transformation was examined with adenosine deaminase (ADA) as a representative membrane protein. ADA's activity changes dramatically in transformed cells and accordingly it is a malignancy marker. Yet, the mechanisms controlling its variable activity are unknown. We undertook the spectroscopic deciphering of its interactions with its lipidic environment in normal and malignant cells. ADA exists in two interconvertible forms, small (45 KD) and large (21OKD). The large form consists of two small catalytic subunits (55-ADA) and a dimeric complexing protein ADCP. The physiological role of ADCP was not known either. Our studies were carried out at three levels.: 1. Solution enzyme kinetics, 2. The interaction of 55-ADA with ADCP reconstituted in liposomes: Effect of cholesterol and 3. Multifrequency phase modulation spectrofluorometry of pyrene-labeled 55-ADA bound to ADCP on the membranes of normal and RSV or RSV Ts68 transformed chick embryo fibroblasts. We found: 1. ADCP has an allosteric regulatory role on 55-ADA, which may be of physiological relevance: It inhibits 55-ADA activity at low physiological adenosine concentrations but accelerates deamination at high substrate concentration. 2. When reconstituted in DMPC liposomes, it retains 55-ADA activity (in its absence the activity is lost) and upon rigidification with cholesterol, a three fold increase in 55-ADA activity is attained, contrary to ADCP's regulatory activity when free of lipids. 3. The reduced ADA activity in transformed chick embryo fibroblasts is associated with increased membrane lipid fluidity (reduced order parameter), reduced accessibility of ADCP and increase rotational dynamics of the complex. We thus obtained spectroscopic deciphering of the vertical motion of ADCP, controlled by lipid-protein interaction, resulting in variable activity of this malignancy marker.

Paper Details

Date Published: 1 May 1990
PDF: 13 pages
Proc. SPIE 1204, Time-Resolved Laser Spectroscopy in Biochemistry II, (1 May 1990); doi: 10.1117/12.17776
Show Author Affiliations
Abraham H. Parola, Ben-Gurion Univ. of the Negev (Israel)
Nurith Porat, Ben-Gurion Univ. of the Negev (Israel)
Valeria R. Caiolfa, Ben-Gurion Univ. of the Negev (Israel)
David Gill, Ben-Gurion Univ. of the Negev (Israel)
Lutz A. Kiesow, Naval Medical Research Institute (United States)
Mathew Weisman, Ben-Gurion Univ. of the Negev (Israel)
S. Nemschitz, Ben-Gurion Univ. of the Negev (Israel)
Dahlia Yaron, Ben-Gurion Univ. of the Negev (Israel)
Karen Singer, Ben-Gurion Univ. of the Negev (Israel)
Ethel Solomon, Ben-Gurion Univ. of the Negev (Israel)

Published in SPIE Proceedings Vol. 1204:
Time-Resolved Laser Spectroscopy in Biochemistry II
Joseph R. Lakowicz, Editor(s)

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