CenA from Cellulomonas fimi is a beta-1,4-endoglucanase that binds tightly to cellulose. X-ray-scattering analyses show that the enzyme is tadpole-shaped: the previously identified catalytic and cellulose-binding domains comprise the head and tail respectively. It appears that this structural and functional organization is common to several cellulases from bacteria and fungi.

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The conformation of the human immunoglobulin molecule Kol [IgG I, xz yz, Gm(f)+] was studied by small-angle X-ray scattering in 0.15 M NaCl solution. The radius of gyration was found to be 5.84 k 0.04 nm, the volume 329 k 15 nm3 and the molecular weight 150000 k 10000.Information on the overall shape was obtained by comparing the experimental scattering curve with the calculated curves for various models. The models were obtained by arranging the models found for the Fab and Fc fragments of the same immunoglobulin molecule in a different manner. A model which fits all the date and the form of the experimental scattering curve is presented.In .recent years the overall structure of various immunoglobulins [l, 21 and their change upon interaction with antigen [3,4] have been studied in solution by small-angle X-ray scattering. The shape of the immunoglobulin G (IgG) molecule was simply approximated by a model composed of a few triaxial bodies. The single fragments Fab and Fc were described by one triaxial body.With the human immunoglobulin molecule Kol and its fragments Fab and Fc we looked for more detailed models which fit the small-angle data better. The investigations on the fragments and detailed models for their structure in solution have been published recently [5]. In this paper the results obtained for the whole IgG molecule Kol are presented. EXPERIMENTAL PROCEDURE Muter iulsThe immunoglobulin molecule Kol has been isolated from the serum of a female patient suffering from multiple myeloma. The methods for its isolation and purification and physicochemical characterisation have been published in detail elsewhere [6,7] and will be mentioned here only briefly.The protein, which is a cryoprotein, was collected by centrifugation of the serum in the cold. The precipitate was washed several times and finally dissolved in the buffer system which was used for the purification of the protein in ion-exchange chromatography. The homogeneity of the isolated protein was shown by electrophoretic and immunoelectrophoretic methods and by serological typing and analytical ultracentrifugation.Finally the protein was crystallised [6,7]; the crystals are suitable for X-ray crystallographic measurements at high resolution [8,9]. Smu 11-Angle X -Ray ScatteringA stabilized high-power X-ray generator (Philips PW 1140) with a tube with copper target delivered a sufficiently high primary intensity (50 kV and 30 mA). A Kratky camera with slit collimation [lo] was used. The scattered intensities were measured at an angle range of 0.00215-0.1 rad using an 120-pm entrance slit.For recording, a proportional counter with an X-ray analysis channel control and measuring system of Philips were used. The pulse height discriminator was focused on the Cu Ka line (0.154 nm). The elimination of the Cu KP line (0.139 nm) was effected by a mathematical procedure using a computer program [l 1 1. A programmable electronic step-scanning device [12] allowed a fully automatized operation which also includes the possibility of a repeated scanning of ...

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