Effect of bredinin and its aglycone on L5178Y cells

The aglycone of the nucleoside antibiotic, bredinin, was as strongly cytotoxic to L5178Y cells as bredinin. The cytotoxic properties of the aglycone were very similar to those of bredinin and the minimum inhibitory concentrations of both were 10(-5)M. The growth inhibitory effects of both agents regardless of their concentrations, were reversed by guanylic acid, guanosine or guanine. However, on increasing the concentrations of these agents, the reversing effect of guanylic acid decreased gradually, the dose-response curves for the two agents being similar. Both agents inhibited the incorporation of thymidine and uridine, but not leucine into macromolecules in L5178Y cells and their inhibitory effects were reversed to similar extents by guanylic acid. On the other hand, the growth inhibitory effect of the aglycone on L5178Y cells was prevented by adenine only, though not be adenosine or adenylic acid while the effect of bredinin was not prevented by adenine. These results suggest that the aglycone itself does not inhibit growth, but that its effect is due to its conversion to bredinin by an enzyme such as adenine phosphoribosyl transferase. For recovery of growth, three moles of adenine were required per mole of the aglycone. When the aglycone was administered orally to rats, bredinin was administered orally to rats, bredinin was recovered in their serum and urine.

Partial purification and properties of cathepsin D in the retinal pigment epithelium

Cathespin D from the retinal pigment epithelium of bovine eyes was purified about 25-fold from a crude extract of retinal pigment epithelium by acid treatment, ammonium sulfate fractionation, and Sephadex G-200 column chromatography. The purified enzyme hydrolyzed bovine serum albumin optimally at pH values close to 4.0. Exposure of the enzyme to 60 degrees C. for 2 minutes resulted in 50 per cent inactivation of the activity. The enzyme activity was completely inhibited by 0.1 microgram per milliliter of pepstatin, slightly inhibited by trasylol, and not affected by soybean trypsin inhibitor. The apparent molecular weight of cathepsin D was estimated to be about 60,000 by gel filtration on Sephadex G-200.

Action of bredinin on mammalian cells

Bredinin, a new nucleoside antibiotic, inhibited multiplication of several mammalian cell lines in culture and had a cytotoxic effect on L5178Y cells. Growth inhibition by bredinin was prevented by guanosine 5'-monophosphate (GMP), guanosine, or guanine but not by other purine or pyrimidine nucleotides, nucleosides, or bases. Inhibition by bredinin at a low GMP; but at higher concentrations of bredinin the inhibition was not reversed even when the concentration of GMP was raised. Addition of GMP after cellular damage had occurred produced no effect on the damaged cells but it prvented further damage. Bredinin caused marked chromosomal aberrations such as breakages, translocations, and fragmentation in L5178Y cells.