Isolation and partial characterization of a protein synthesis inhibitor from brine shrimp embryos.

Encysted embryos of the brine shrimp, Artemia salina, contain an inhibitor of protein synthesis that appears to be important in translational control. In cyst homogenates, the inhibitor appears to be partitioned almost equally between the cytosol and ribosome fractions and it has been purified from both fractions to near homogeneity. In a cell-free protein-synthesizing system derived from Artemia cysts, with poly(U) as messenger, the protein inhibits polyphenylalanine synthesis proportional to inhibitor concentration up to about 75% inhibition, and the primary site of action appears to be at the elongation step. The inhibitor activity is not altered by 50-150 mM KCl in the reaction mixture, but it is slightly more effective at 5 mM MgCl2 than at 10 mM MgCl2. The inhibitor is a heat-labile protein of 130000 molecular weight and is devoid of hydrolase activity. Our data indicate that the inhibitor is not elongation factor EF-1 or EF-2, but we are studying the possibility that it may be a modified form of elongation factor EF-2.

L-ascorbate 2-sulfate and mobilization of cholesterol from plaque deposited in rabbit aortas.

Rabbits were randomly assigned to two groups. Age and body weight distribution were equal in both groups. All animals were placed on a high cholesterol diet for 9 wk, then returned to a normal diet for 1 wk. At the end of this dietary regimen, one group of animals received subcutaneous injections of psysiological saline 3 times/day, 5 days/wk for 10 wk, and the other group recieved L-ascorbate 2-sulfate (0.37 mmole) according to the same timetable. On alternate weeks, the serum levels of total and free cholesterol were determined. After 10 wk of treatment the animals were killed; the plaques were excised from the aortas and examined for total mass and cholesterol content. We observed that, under these dietary conditions, L-ascorbate 2-sulfate does not mobilize cholesterol or its esters from preformed aortic plaque. However, we did observe that animals showing high cholesterol levels in their sera died prematurely when injected with L-ascorbate 2-sulfate. Gross and histopathological investigations of organs and tissues did not reveal any significant differences among the animals that died prematurely and those that survived to the termination of the experiment.

L-ascorbic acid, L-ascorbate 2-sulfate, and atherogenesis.

Rabbits on a high cholesterol diet were divided into three groups: one group received subcutaneous injections of physiological saline 3 times/day, 5 days/wk for 10 wk; another group received subcutaneous injections of L-ascorbic acid (0.37 mmole) according to the same timetable; and the third group was administered an equivalent amount of L-ascorbate 2-sulfate as outlined above. Each week the serum levels of total and free cholesterol and triglycerides were measured. At the end of 10 wk the animals were killed and the cholesterol content of the livers, spleens, and adrenal glands was measured. The aortas were examined for plaque deposition; the deposits were excised and pooled according to groups; and the total mass and cholesterol contents of the pooled plaques were determined. Administration of ascorbic acid or ascorbate 2-sulfate did not prevent hypercholesterolemia or elevated levels of serum triglycerides. No significant differences among the groups were found either in tissue cholesterol levels or in the extent or type of lesions found. Although plaque deposition appeared to be similar in the aortas of these animals, a marked difference was found in total mass and cholesterol content of the plaques: The plaques of the saline-treated group had a total mass and cholesterol content approximately 2.5 times that found in the group injected with ascorbic acid and about 1.5 times that found in the animals treated with ascorbate 2-sulfate. These results indicate that ascorbic acid, in particular, minimizes the total quantity of plaque deposition even though it is ineffective in preventing hypercholesterolemia, elevated serum triglycerides, and accumulation of cholesterol by several tissues.