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ISOLATION AND STUDY OF A FRAGMENT OF HUMAN SERUM ALBUMIN CONTAINING ONE OF THE ANTIGENIC SITES OF THE WHOLE MOLECULE.

1. A fragment of human serum albumin called ;inhibitor' has been degraded by trypsin, and one of the degradation products, designated fragment F1, has been isolated. Fragment F1 has a molecular weight of 6600. It contains neither tyrosine nor tryptophan. It is not precipitated with rabbit anti-sera to human serum albumin. 2. Fragment F1 was coupled to p-aminobenzylcellulose to form an insoluble conjugate. Rabbit anti-(human serum albumin) antibodies reacting with fragment F1 were specifically adsorbed on this conjugate and were desorbed by glycine-hydrochloric acid buffer. The isolated antibodies are composed of gamma-globulin and beta(2)-macroglobulin. 3. Human serum albumin and fragment F1 formed with 7s anti-(fragment F1) antibodies soluble complexes that were studied by passive haemagglutination, ultracentrifugation and electrophoresis. Fragment F1 was shown to contain only one of the antigenic sites of albumin molecule. The 7s anti-(fragment F1) antibodies were shown to be bivalent and monospecific.

Animals↗

PHOTOMETRIC EVIDENCE FOR THE OSMOTIC BEHAVIOR OF RAT LIVER MICROSOMES.

Electron microscope observations are consistent with the interpretation that the elements of the endoplasmic reticulum are osmotically active in situ as well as after isolation. More recently, it has been reported that microsomal suspensions equilibrate almost completely with added C(14)-sucrose and that no osmotic behavior is evident from photometric data. These findings were considered at variance with the electron microscope data. However, equilibration with added label simply attests to a relatively high permeability, and, in addition, the photometric data need not be critical. Osmotic volume changes, measured photometrically, may be masked by concomitant events (e.g., changes in the refractive index of the test solutions at varying osmotic pressures, breakdown of the particles, and agglutination). For these reasons the photometric experiments were repeated. In this work, the reciprocal of optical density of microsomal suspensions was found to vary linearly with the reciprocal of concentration of the medium at constant refractive index. These changes probably correspond to osmotic volume changes, since the effect was found to be (a) independent of substance used and (b) osmotically reversible. The transmission of the suspension was found to vary with the refractive index of the medium, the concentration of particles, and the wavelength of incident light, according to relationships that are similar to or identical with those obtained for mitochondrial suspensions.

Animals↗