ABSTRACT
The interaction between the antibody and the corresponding target molecule determines the characteristics of immunoassay. In this study, a single chain variable fragment antibody (scFv4C7) derived from the hybridoma strain 4C7 were prepared via genetic engineering technique. The recognition properties of scFv4 C7 was determined and compared to those of the parent monoclonal antibody by indirect competitive enzyme-linked immunosorbent assay(ic-ELISA). Three dimensional structure of the scFv4C7 was presented by Swiss-Model, and sulfathiazole ( STZ) was docked to the scFv4C7 model to obtain the structure of the binding complex. The results from the ic-ELISA showed that the binding properties of scFv4C7 were comparable with the parent monoclonal antibody and STZ was almost completely buried in a deep binding pocket formed by the heavy chain and light chain of the antibody. The interaction between STZ and scFv4C7 was more closely related to the heavy chain and the complementarity-determining region ( CDR ) H3 loop played more important role than other CDR loops. The study preliminary provided the necessary structural information for the preparation of antibody with broader specificity and higher affinity.
ABSTRACT
While attempting to purify UDP-galactose 4-epimerase from carp liver extract at pH 8.0, it was observed that the preparation even after dialysis could reduce NAD to NADH, interfering epimerase assay. The NAD reduction activity and the epimerase were co-eluted in a series of chromatographic steps. Mass spectrometric analysis of semi-purified fraction revealed that carp liver lactate dehydrogenase (LDH) contained bound lactate which was converted to pyruvate in the presence of NAD. The enzyme-bound lactate and the association with epimerase stabilized LDH from trypsin digestion and thermal inactivation at 45°C by factors of 2.7 and 4.2 respectively, as compared to substrate-free LDH. LDH and epimerase do not belong to any one pathway, but are the rate-limiting enzymes of two different pathways of carbohydrate metabolism. Typically, strongly associated enzymes work in combination, such as two enzymes of the same metabolic pathway. In that background, co-purification of LDH and epimerase as reloaded in this study was an unusual phenomenon.