Insulin therapy in adult patients hospitalized for a critical illness, other than hyperglycemic crises, may decrease mortality in certain groups of patients.

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Electron micrographs are shown ofthe first component of human complement (CI) which has been crosslinked with a water-soluble carbodiimide to prevent dissociation into its Clq and Clr2Cls2 subunits. Two projections of the crosslinked molecule are seen in the electron micrographs, which are called "top" and "profile. " In both views, the Clq heads are visible. From the top, the Clr2Cls2 tetrameric subunit appears to be located centrally on the Clq and folded to form a compact mass obscuring most of the arms and central bundle. In profile, the tetramer appears to be located in the region of the arms between the Clq heads and the central bundle. Both the heads and the rod-like central bundle appear to be free of Clr2Cls2 in these profile projections. Sometimes it is possible to count more than six domains in the region ofthe Clq heads, as though a portion ofthe tetramer had unfolded to protrude among the heads.Excellent electron micrographs ofClq (1-4) and ofthe Clr2Cls2 tetramer have been published (5), as well as hydrodynamic studies on Clq, Clr2Cls2, and C1 (5-12). Clq has the appearance of a bouquet of tulips (13); Clr2Cls2 resembles a rod with bent ends (5). Reassembled C1, which spontaneously re-forms when one subunit of Clq is mixed with one tetrameric subunit of Clr2Cls2 in the presence of Ca2+, has hydrodynamic properties consistent with a 1-to-i complex (ref. 12; unpublished data) but the ultrastructure of the complex has remained an intriguing mystery, perhaps due to a tendency of C1 to dissociate when it adheres to a carbon-coated grid. We have successfully stabilized the C1 complex by treatment with a water-soluble carbodiimide and have succeeded in obtaining electron micrographs of this fascinating and unusual macromolecule. METHODSPreparation of Clr2C1s2. A modification of the procedure described by Medicus and Chapius (14) was used to purify Clr2Cls2. Diluted serum was pumped at a flow rate of200 mV hr, through a 2 x 30 cm rabbit IgG-Sepharose affinity column, strictly at 40C, in the presence of 30 ,uM p-nitrophenylguanidinobenzoate (NPGB). Next, the column was washed with 200 ml of a 1:1 mixture of 0.1% gelatin/0.15 mM CaCl2/L mM MgCl2 in Veronal-buffered saline (GVB) and 9.7% sucrose/ 0.15 mM CaCl2/l mM MgCl2 in Veronal-buffered saline (SVB) and then 500 ml of Veronal-buffered saline (VBS), containing NPGB. The subcomponents Clr and Cls were eluted with VBS/ 25 mM EDTA/4.85% sucrose/30 ,uM NPGB (250 ml), concentrated by ultrafiltration through a YM 10 membrane (Amicon, Lexington, MA), and reconstituted to form the Clr2Cls2 complex by dialysis against 0.01 M Tris/0. 15 M NaCl (TBS) at pH 7.3 containing 5 mM Ca2+. The reconstituted Clr2Cls2 was loaded onto a 2 X 100 cm Sepharose 4B column and eluted with TBS at pH 7.3 containing 5 mM Ca2+. The symmetrical portion of the first protein peak was pooled and concentrated by ultrafiltration. The preparation was shown to contain Clr and Cls by immunodiffusion with specific anti-Cir and anti-Cis antisera (Atlantic Antibodies, Scarborough, ME)....