Are polyclonal catalytic antibodies heterogeneous?

Abstract

Following the first demonstration of antibody-mediated catalysis in 1986 [ 1,2] most investigations have been concerned with monoclonal antibodies [3-51. Another aspect of the field is concerned with polyclonal catalytic antibodies. The finding (reviewed in [6]) that, despite early discouraging results [7,8], substantial catalytic activities can be generated reproducibly in polyclonal preparations [9141 suggests valuable opportunities for studies and applications complementary to those involving monoclonal catalytic antibodies. The particular value of the former was pointed out in [lo] and emphasised by others [6,12-151. Because polyclonal IgG necessarily represents the entirety of the immune response, the relative immunogenic capabilities of a series of haptens may be assessed more effectively than by studies on a small selection of isolated monoclonal antibodies[ 141. A potential problem in the evaluation of the catalytic activity of polyclonal IgG is that heterogeneity might result in complex kinetic behaviour. We have reported the kinetic characteristics of catalyticallyactive polyclonal IgG preparations purified from sheep serum [9-121. IgG from sheep immunised with a 4-nitrophenylphosphate-keyholelimpet haemocyanin (KLH) conjugate (I) was shown to catalyse the hydrolysis of the analogous 4-nitrophenyl carbonate (11) at pH 8.0. It is an important observation that the catalysis obeyed the Michaelis-Menten equation (at least in the range of [S] studied, ca 0.2-17pM). This provides no evidence for functional heterogeneity in the various IgG preparations. As is well known, catalysis by mixtures of enzymes with significantly different characteristics deviates from adherence to the Michaelis-Menten equation such that plots of [S]/V~ versus [S] are markedly curved concave downwards [16]. H H