Vitamin B12-binding proteins of the horseshoe crab Limulus polyphemus.

Vitamin B12-binding proteins were detected in the body fluids and/or tissues of horseshoe crabs (Limulus polyphemus), clams and sponges. Among the biological specimens tested the Limulus plasma was especially rich in free B12-binding proteins. Gel filtration experiments revealed that Limulus plasma contains two classes of B12-binding proteins.

Drug-induced suppression of phospholipid synthesis in HeLa cells by inhibition of choline uptake.

2-(4-Anisidino)-4,6-bis (2-(diethylmethylammonium)ethylamino)-1,3,5-triazine diiodide was found to inhibit specifically the incorporation of [14 C]-choline into cold 5 percent trichloroacetic acid-insoluble materials in HeLa cells without affecting other vital areas of cellular metabolism. Further studies indicated that this drug did not affect any of the intracellular reactions leading to phosphatidylcholine formation; instead, the inhibition of lecithin synthesis was due primarily to the suppression of choline transport through the cytoplasmic membrane. The level of inhibition of the latter process was comparable to that observed for the inhibition of choline incorporation into cold 5 percent trichloroacetic acid-insoluble precipitates in whole cells.

Dependence of diaminopurine utilization on the mutational site of purine auxotrophy in Bacillus subtilis. II. Tracer experiments.

Tracer experiments were carried out in an attempt to explain why guanineless auxotrophs can use diaminopurine as a guanine replacement but nonexacting purine auxotrophs cannot do so. Cell suspensions of the nonexacting purineless Bacillus subtilis MB-1356 incorporated more radioactivity from diaminopurine-2-(14)C into nucleic acid than did guanineless B. subtilis MB-1517.