[Urea cycle enzymes in rats fed with corn]. / Enzimas del ciclo de la urea en ratas alimentadas con maíz.

Activities of five urea cycle enzymes, carbamyl phosphate synthetase, ornithine transcarbamylase, argininosuccinate synthetase, argininosuccinase and arginase, were measured in liver of rats fed two types of diet: diet I: raw common corn and, diet II: made of a mixture of corn starch ("maicena"), "chuño (dried potato), sugar and fat. The activities obtained were compared with those of a group of control rats fed a balanced diet with an adequate protein content. Diets were administered after weaning, through an experimental period of 90 days, and enzymatic activities were measured at regular intervals during this time. Animals raised on diet I as well as those raised on diet II, showed low activity of the five urea cycle enzymes, but the decrease of enzymatic activity was more pronounced and appeared earlier in animals raised on diet II. Carbamyl phosphate synthetase and argininosuccinate synthetase, the two synthetases of this cycle, decreased earlier and in a greater degree than the other three enzymes in animals raised on these two types of diet.

[DNA and proteins in the liver of rats fed with corn: the importance of expressing the concentration of liver proteins in relation to DNA]. / DNA y proteínas en el hígado de ratas alimentadas con maíz: importancia de expresar la concentración proteínas hepáticas en función del DNA.

Variations in liver DNA and protein content were studied in rats fed common corn (diet I) and in another group of rats fed a diet made of corn starch ("maicena"), "chuño" (dried potato), sugar and fat (diet II). The results were compared with those from a control group fed a balanced diet with adequate protein. Diets were administered after weaning, for a period of 90 days. Animals on diets I and II showed an increase in the DNA concentrations per g of liver. Liver protein concentration was expressed in three forms: as mg of protein per g of liver, mg of protein per mg of DNA and mg of protein in the total liver weight. Animals raised on diet II had a decrease in liver protein, which was evident regardless of the way of expressing the results. On the other hand, in rats raised on corn (diet I), the results expressed as mg of protein per g of liver did not show a decrease in liver proteins, while the other two ways of expressing the results demonstrated a decrease in liver protein. It seems that the most trustworthy way to express liver protein concentration is as mg of protein per mg of DNA. The importance of expressing the results of liver protein concentrations as a function of DNA is emphasized and its usefulness demonstrated and discussed.

Isolation and characterization of polyribosomes from the salivary glands of Rhynchosciara americana.

Polyribosomes were obtained in high yield from Rhynchosciara salivary glands by a method which uses the non-ionic detergent Nonidet P 40, in moderate salt buffer and DTT as RNase inhibitor. The polysomal profiles from glands of animals which have just started to spin the communal cocoon are slightly but consistently different from those obtained from about 5 day older animals, in which DNA puffs were open in the salivary gland chromosomes. The heaviest polyribosomes which could be detected by either radioactive uridine or amino acid incorporation have 8 to 9 ribosomes. The data indicate the existence of stable messengers in the salivary glands.