STUDIES ON EPITHELIAL CELLS ISOLATED FROM GUINEA PIG SMALL INTESTINE

Sheets of mucosal epithelial cells were released from guinea pig small intestine after incubation with ethylenediaminetetraacetate. Cells in sheets retained their columnar shape for 24 hr at room temperature, and exclusion of nigrosine suggested they had intact plasma membranes. When sheets were disaggregated individual cells had normal morphology for at least 4 hr. During isolation 16% of the total protein and 24% of the total lactic dehydrogenase were lost from the cells, but subsequent enzyme leakage was low. Leakage increased with shaking, incubation at 37°C, or increasing the oxygen tension of the suspending medium, but was minimal when the Na⁺:K⁺ ratio in the medium was 8:1 and the osmolarity was high. Losses of particulate enzyme activities were negligible. Respiration was constant for up to 4 hr and was insensitive to calcium, bicarbonate, oxygen tension, and pH. It was inhibited by cyanide and iodoacetate and varied with the Na⁺:K⁺ ratio of the extracellular fluid and the structural integrity of the cells. All preparations concentrated potassium and excluded sodium, but lost this ability if ouabain was added or cells were broken. Potassium-42 uptake was also sensitive to temperature, ouabain, and structural integrity. The preparations are being used to study cell metabolism in the intestinal epithelium.     

Guinea-pig liver tryptophan pyrrolase. Absence of detectable apoenzyme activity and of hormonal induction by cortisol and possible regulation by tryptophan

1. When assayed in fresh homogenates, guinea-pig liver tryptophan pyrrolase exists only as holoenzyme. It does not respond to agents that activate or inhibit the rat liver enzyme in vitro. Only by aging (for 30min at 5 degrees C) does the guinea-pig enzyme develop a requirement for ascorbate. 2. The guinea-pig liver enzyme is activated by the administration of tryptophan but not cortisol, salicylate, ethanol or 5-aminolaevulinate. 3. The tryptophan enhancement of the guinea-pig liver pyrrolase activity is prevented by 0, 34 and 86% by pretreatment with actinomycin D, cycloheximide or allopurinol respectively. 4. The guinea-pig liver tryptophan pyrrolase is more sensitive to tryptophan administration than is the rat enzyme. On the other hand, the concentrations of tryptophan in sera and livers of guinea pigs are 45-52% less than those in rats. 5. It is suggested that tryptophan may regulate the activity of guinea-pig liver tryptophan pyrrolase by mobilizing a latent form of the enzyme whose primary function is the detoxication of its substrate.     

Interaction of the glucose tolerance factor (GTF) with insulin

Partially purified glucose tolerance factor (GTF) which had been extracted from Brewer's yeast was mixed with ¹²⁵I-insulin, and the solution was chromatographed on Sephadex G-50. Similarly, ¹²⁵I-insulin which had not been reacted with GTF was chromatographed. Insulin reacted with GTF produced a significantly greater effect on glucose uptake in epididymal tissue than that of native insulin. When GTF, exclusive of insulin, was chromatographed, the fraction which potentiated insulin activity had an elution volume greater than that of insulin. These results demonstrate that GTF binds to insulin. When insulin was reacted with acetic anhydride under conditions which acetylate the α and ε amino groups, GTF binding to insulin was inhibited. These results suggest that the α and ε amino groups of insulin may be involved in the binding of GTF to insulin.     

A re-evaluation of polypodium bradeorum and P. Colysoides

During field studies on the pteridophytes of Costa Rica, a peculiarly dimorphic polypodioid fern was found in the rain-forests of the Atlantic lowlands near Puerto Viejo. The variation in the fertile frond, ranging from simple and short petiolate to pinnatisect and long petiolate, coupled with peculiarly elongate and irregular sori, prompted further investigations. Additional herbarium specimens from localities in Mexico, British Honduras, Nicaragua, and Costa Rica showed intermixed variations between plants with all leaves simple (typified byPolypodium bradeorum Rosenstock) to plants with all leaves lobed or pinnatisect (typified byP. colysoides Maxon & Copeland). Other characters were judged sufficiently homogeneous to consider these individuals as conspecific underP. bradeorum. Morphological studies indicate parallel evolution of several characters in the Asiatic generaColysis, Microsorium, andLeptochilus on the one hand and the New World members ofMicro gramma, Pleopeltis, andPolypodium bradeorum on the other