Jmol is free, open source software for interactive molecular visualization. Since it is written in the Java™ programming language, it is compatible with all major operating systems and, in the applet form, with most modern web browsers. This article summarizes Jmol development and features that make it a valid and promising replacement for Rasmol and Chime in the development of educational materials, as well as in basic investigation of biomolecular structure. The description is set up by comparison with the well known abilities of Rasmol and Chime. Jmol is suitable for molecular model display and analysis in biochemistry, molecular biology, organic and inorganic chemistry, crystallography, and materials science.

Red blood cells (RBC) modified with biotin and streptavidin (SA) present an interesting potential drug delivery system. Biotinylation and SA attachment, however, alter the biocompatibility of RBC. We have reported that polyvalent SA attachment induces lysis of biotinylated RBC (b-RBC) by homologous complement via the alternative pathway. Lysis occurs due to inactivation of the membrane regulators of complement, DAF and CD59, cross-linked by SA. However, monovalent SA attachment does not induce lysis. On the basis of these findings we hypothesized that reduction of the biotin surface density on b-RBC would allow for monovalent SA attachment to b-RBC and that such SA/b-RBC should then be stable in the circulation. In the present work we injected into rats several different radiolabeled RBC probes: rat RBC biotinylated to varying degrees (b_n-RBC, where b_nrepresents the input micromolar concentration of biotinylating agent), as well as SA/b_n-RBC. Extensively biotinylated rat RBC (b₇₀₀-RBC, stable in serumin vitro) were rapidly cleared from the bloodstream. We further found that extensively biotinylated human b₁₀₀₀-RBC bound C3b from serumin vitrowithout detectable lysis, and that rat b₇₀₀-RBC bound to isolated macrophages in a complement-dependent fashion. Therefore, nonlytic C3b fixation and uptake of C3b-carrying b₇₀₀-RBC by macrophages appears to be the mechanism leading to clearance of b₇₀₀-RBCin vivo.Moderately biotinylated RBC (b₇₀-RBC and b₂₄₀-RBC) were stable in serumin vitro.SA attachment to b₂₄₀-RBC led to their rapid lysis in serumin vitro,lysis in the bloodstream, and clearance by the liver and spleen. SA attachment to b₇₀-RBC led to fast elimination of SA/b₇₀-RBC from the bloodstream, whilein vitroSA/b₇₀-RBC were stable in serum. Modestly biotinylated RBC (b₂₃-RBC) demonstrated only marginally decreased 60-min survival in the bloodstream regardless of SA attachment. Ourin vitrostudies indicate that b₂₃-RBC bound approximately 10⁵SA molecules per cell, and the resulting SA/b₂₃-RBC bound 5 × 10⁴molecules of biotinylated IgG (b-IgG) per cell. About 60% of the injected dose of b-IgG/SA/b₂₃-RBC labeled with⁵¹Cr was detected in the rat blood cells 1 day after iv injection. To assess whether b-IgG/SA/b₂₃-RBC circulate in the bloodstream as a stable complex, we have injected¹²⁵I-labeled b-IgG/SA/⁵¹Cr-labeled b₂₃-RBC in rats. Up to 60 min after injection, both radiolabels display similar level in bloodstream. Up to 3 h after injection, about 70% of¹²⁵I was detected in the blood cells. In contrast, 100% of¹²⁵I was detected in plasma after injection of nonconjugated¹²⁵I-labeled b-IgG. Thus, major portion of SA/b₂₃-RBC-attached b-IgG circulates as a complex with RBC. About 30% of RBC-bound b-IgG undergoes detachment from the carrier b-RBC, probably in the pulmonary capillaries, because lung level of¹²⁵I was twice as high as that of⁵¹Cr. Therefore, the surface density of biotin on the b-RBC membrane appears to play a key role in regulating complement-mediated clearance of b_n-RBC and SA/b_n-RBC from the bloodstream. Modest biotinylation generates b-IgG/SA/b₂₃-RBC circulating for several hours as stable immunoerythrocytes without detectable lysis or marked elimination, and it may be possible to use these RBC in a drug delivery system.

Polyethylene glycol (PEG) modification of a chimeric Fab' fragment (F9) of A5B7 (alpha-CEA), using an improved coupling method, increases its specificity for subcutaneous LS174T tumours. PEGylation increased the area under the concentration-time curve (AUC0-144) in all tissues but there were significant differences (variance ratio test, F = 27.95, P < 0.001) between the proportional increases in AUC0-144, with the tumour showing the greatest increase. The increase in AUCtumour from F9 to PEG-F9 was similar to the reported increase from Fab' to F(ab')2 while the increase in AUCblood by PEGylation of F9 was only 21% of the reported increase from Fab' to whole IgG. A two sample t-test showed no significant differences between maximal tumour/tissue ratios for PEG-F9 and F9 while the tumour/tissue ratios for PEG-F9 remained high over a longer period, with tumour levels at least double those for F9. PEG-F9 emerges as a new generation antibody with potential advantages for both radioimmunotherapy and tumour imaging. Since there was a reduction in antigen binding, optimisation of PEGylation might further improve tumour specificity. The latter resulted from complex effects on both the entry into and exit rates from tumour and normal tissues in a tissue-specific fashion.