On a colloidal solution for the functional examination of human reticuloendothelial system that will withstand the intra venous injection, Kobayashi of our laboratory and the author have proposed the following requirements as essential: 1) that it should not become a source of heterogenous protein; 2) that it should be readily sterilized; 3) that it should be easily prepared and radioisotope can readily be added to it: 4) that its granule distribution is colloidchemically adequate and the diameter of granules is uniform in size; 5) that it is stable and can be harvested for use any time after storage; and 6) that, after being phagocytized by the reticuloendotheilal system in vivo, it would enter the next metabolic step effectively without eliciting inhibitory phenomenon and should be not harmful in vivo.
However, we have as yet no colloidal solutions that meet satisfactorily these conditions. Therefore, the authors have selected some of iron colloids that are of loose binding in nature for this purpose, and conducted a series of screening texts with them. As the result it has been possible to prepare several new loose-binding iron colloid solutions. The present communication deals briefly with the colloidal chemical properties of these preparations.
The conclusions reached may be stated as follows:
1. It has been found that glycyl-lycine iron colloid, serum iron colloid, chondroitin iron phosphate colloid, glutamic iron colloid, and ATP iron colloid are all loose-binding colloids, and with only a slight lowering of pH, Fe… can readily be released, without causing iron-blocking in the reticulo-endothelial system, and thus enabling Fe… to enter readily into the next metabolic step.
2. More than 80% of glycyl-lycine irrn colloid is cmposed of colloidal granules of the size ranging 400-800Å, being approximately uniform in size and distributed evenly, and when brought in contact with serum or plasma its granule distribution becomes more satisfactory.
3. When 100 mg glycyl-lycine is made to bind to Fe…, up to 3 mg equivaleut of Fe… turn to a stable sol.
4. Glycyl-lycine iron colloid stays in the form of sol at the pH between 5.7 and 8.4, but it transforms to lyogel below pH 5.6, and above pH 8.5 to coagel.
5. Glycyl-lychine iron colloid can be prepared raedily and it can be sterilized completely.
6. Even when glycyl-lycine iron colloid tranforms from sol to gel, the size of individual colloidal granules remains unchanged excepts for the change in the size of micelles, and the colloid form of sol and gel is reversible by the change of pH.
These results have verified conclusively that glycyl-lycine iron colloid is almost an ideal colloid for the use in examining the function of human reticulo-endothelial system, judging from its chemical properties