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One of these isolectins has four “E” subunits and is designated PHA-E. PHA-E possesses strong hemagglutinating activity but is a poor mitogen. PHA-L, with four “L” type subunits, does not agglutinate red cells but is a potent mitogen. The other three isolectins, designated E3L1, E2L2, and E1L3, have erythroagglutinating and mitogenic activities proportional to the number of respective “E” or “L” subunits. We have termed the mixture of the five isolectins PHA (E+L). All of these isolectins are glycoproteins with molecular weights of approximately 125,000 and have isoelectric points between pH 5.2 for PHA-L and pH 6.0 for PHA-E.
PHA-L, although a potent mitogen, has a rather narrow range of concentrations for mitogenic stimulation and appears to require calcium and manganese ions for activity. The presence of some “E” subunits in PHA appears to broaden the concentration range of maximum mitogenic stimulation. As a consequence, PHA (E+L) may be preferred for general mitogenic assays. PHA-L has been found to be an excellent, specific marker for use in anterograde neuronal tracing. |