Phone: (787) 764-0000 ext. 4782
Ph.D., Rutgers University, 1976.
Biochemistry: The Organization of Lipids in Biological Membranes and the Role Played by the Acyl Composition of Phospholipids. To this end phospholipases A2 from different sources and covalent conjugates of these enzymes with receptor binding proteins have been developed as probes of the two-dimensional organization of membrane surfaces.
In our laboratory we are using phospholipases A2, isolated from different snake venoms to probe the organization and dynamics of phospholipids on cell surfaces. Our findings have indicated that phospholipid species are distributed in a non-random manner on the external surface of intact erythrocytes and those species which contain acyl chains with four or more double bonds are usually in the proximity of integral membrane proteins. One of the major lines of evidence which supports these findings being that normally non-specific Group IA phospholipases can be made specific toward arachidonate containing species by cross-linking these enzymes to lectins which bind cell surface proteins. In addition, a Group II phospholipase which binds tightly to a very limited number of cell surface sites is specific for arachidonate containing species only at enzyme concentrations which do not saturate these sites. We are currently characterizing the cell surface protein which binds to this Group II phospholipase.
Several on-going projects take advantage of the discovery that different phospholipases can probe different membrane domains. For example, low levels of several anti-inflamatory agents, local anesthetics and cationic lipophiles have been found to induce significant effects on the activity of these phospholipases, but since these are not specific with respect to phospholipase, they are probably a result of a general perturbation of the membrane. On the other hand, certain amphipathic peptides, particularly the mast cell degranulation peptides, have shown to affect
only the activity of the specific Group II phospholipase, indicating that these peptides probably interact with annular lipids. In the case of prostaglandins, PGE1 and PGE2, time-dependent changes in activity and specificity are also limited to the specific Group II phospholipase.
Long term plans call for the isolation and characterization of other secreted phospholipases which are capable of interacting with specific receptors on cell surfaces. Identifying the effects of physiologically relevant agents on the activity of phospholipases which bind to specific receptors will provide much needed and useful information on the function and role of lipids in membranes.
Litchfield, C., Greengerg, A.J., Noto, G. and Morales, R.W., Unusually High Levels of C24-C30 Fatty Acids in Sponges of the Class Demospongiae, Lipids, 1978, 11, 244-247.