Enzyme inhibition by antibodies

Abstract

The interest in the inhibition of enzymes by their specific antibodies stems mainly from the fact that these systems can serve as suitable models in the study of neutralization of biologically active molecules in general. The interaction of enzymes with their specific antibodies generally leads to a reduction in their enzymatic activity. The mechanism of this inhibition is rarely a direct combination of the antibodies with the catalytic site, but is rather due to steric hindrance, namely, barring the access to the active site. In several systems the mechanism of the antibody effect is by conformational changes which it induces on the enzyme. In these cases, the interaction with the antibody may result either in inhibition or in enhancement of the enzymatic activity. In every instance, however, the effect of the antibody is dependent on its narrow specificity, namely, on the regions of the enzyme to which it is directed. The extent of inhibition or enhancement is, therefore, a reflection of the nature and distribution of the various antigenic determinants on the enzyme molecule. Antibodies specific exclusively to defined regions of an enzyme molecule can be prepared. This has been performed for both lysozyme and staphylococcal nuclease by two procedures: a) Selective separation of the relevant antibodies from the anti-enzyme serum by an immunoadsorbent containing a particular immunologically active fragment of the enzyme. b) The use of an isolated antigenic fragment of the enzyme, or a conjugate of it, for immunization. The antibodies thus prepared, specific toward a unique defined region of the lysozyme molecule (residues 60-83, denoted "loop") recognize the structural conformation of the fragment and are reactive with the intact enzyme molecule. Furthermore, a chemically synthesized loop-like derivative was proved immunologically identical with the natural fragment, and when forming a part of a completely synthetic conjugate, elicited conformation-specific antibodies, reactive with native lysozyme. These findings are relevant to the topic of an immunological approach to fertility control from two different viewpoints: In the first place they are informative regarding the specific inhibition by antibodies of sperm enzymes which partake in the fertilization process. Secondly, they encourage the synthetic approach for induction of an immune response toward hormones which are crucial in fertilization or implantation.