A heme-octapeptide (mol wt 1,550) has been obtained from cytochrome c by successive pepsin and trypsin hydrolysis and purified by gel filtration and countercurrent distribution. It possesses peroxidatic activity characterized by an apparent Km of 0.2 M, an apparent vmax of 4 mmol/min per mg of peptide, and a pH optimum of 7.0. Using a novel two-step conjugation procedure, the heme-octapeptide was coupled to rabbit Fab antibody fragments by first derivatizing it with the N-hydroxysuccinimide ester of p-formylbenzoic acid and subsequently allowing it to form a Schiff base with the amino groups of Fab. Stable covalent linkages were then obtained by reduction of the Schiff bases with sodium borohydride. The conjugate consists of ∼2 heme-octapeptides attached to each Fab molecule. The molecular weight is 45,000 daltons when coupled to sheep Fab and 50,000 daltons with a Stokes radius of 32 Å, when conjugated to rabbit Fab. Its peroxidatic activity is characterized by an apparent Km of 0.4 M, an apparent vmax of 0.4 mmol/min and per mg of attached heme-octapeptide and a pH optimum of 7.0. The conjugate has been used for the localization at the electron microscope level of secretory immunoglobulins in the mammary gland of lactating rabbits.
PREPARATION AND CHARACTERIZATION OF AN IMMUNOELECTRON MICROSCOPE TRACER CONSISTING OF A HEME-OCTAPEPTIDE COUPLED TO Fab
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J. P. Kraehenbuhl, R. E. Galardy, J. D. Jamieson; PREPARATION AND CHARACTERIZATION OF AN IMMUNOELECTRON MICROSCOPE TRACER CONSISTING OF A HEME-OCTAPEPTIDE COUPLED TO Fab . J Exp Med 1 January 1974; 139 (1): 208–223. doi: https://doi.org/10.1084/jem.139.1.208
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