SYNOPSIS. In chemically defined media at carbohydrate concentrations ≧ 0.5% (w/v) Tetrahymena pyriformis W multiplied more rapidly, developed larger cells, and achieved greater growth as measured by optical density when carbohydrate was provided as dextrin rather than glucose. In media containing 0.3 mg/ml of amino acid nitrogen, growth increased with glucose concentration from 0.1 to 1%, did not change significantly to 3%, and was sharply inhibited at higher glucose levels. With dextrin, maximum growth paralleled carbohydrate concentration from 0.1 to 3%. At higher N levels the inhibitory concentration of glucose was lowered, but growth in dextrin media was not affected except at N concentrations that were inhibitory independent of carbohydrate source. At 1% carbohydrate levels, total cell protein per ml of culture was 60% greater, protein per cell approximately 50% greater, and cells were 1.5 to 2 times larger in media with dextrin than with glucose. Comparable differences in protein synthesis were observed at 2% carbohydrate levels and efficiency of conversion of substrate‐N to protein‐N was greater in the medium with dextrin than glucose. Growth as measured by optical density in media with 0.3 mg/ml of N and 1 or 2% (w/v) of dextrin was not significantly reduced by the simultaneous presence of 1 or 2% glucose. This observation appeared to negate osmotic pressure as an explanation of reduced growth in the presence of glucose. At higher osmolar concentrations osmotic pressure appeared to be a major determinant of overall growth but not of cell size.

Growth inhibition of Tetrahymena pyriformis by L-serine in a chemically defined medium was reversed by L-arginine in a manner which resembled competitive antagonism. Composition of the free amino acid pools from cells grown in either a balanced amino acid mixture or a mixture with serine concentrations which inhibited growth suggested an antagonism by serine with energy-yielding reactions. Growth in media with excess serine resulted in the accumulation of higher concentrations of free cellular amino acids and an apparent increase in the rate of conversion of arginine to ornithine, as compared with growth in the balanced medium. The results suggested that serine or a metabolic product of serine interferes with the formation of pyruvic acid. In the presence of high levels of serine, arginine appeared to be metabolized more rapidly and to be spared when alanine, aspartic acid, or glutamic acid was added to the unbalanced medium.

1052AFLATOXIN EFFECT ON DNA POLYMERASE against insulin as a source folr this biologic effect. In this respect the activity closely resembles the "atypical" serum insulin described by Samaan et aZ(9,lO); however, the present characterization of UILA from an obese human subject suggests that it is more closely related to albumin than to unmodified insulin.Summary. The insulin-like activity found in urine protein from obese subjects during fasting was characterized by benmic acid precipitate and Sephadex column chromatography. The major portion of the urine insulin-like activity was found in a single protein peak which was homogeneous by polyacrylamlide gel electrophoresis, and its electrophoretic mobility was identical to human serum albumin. This active fraction was significantly neutralized by rabbit antiserum to human serum albumin. These results suggest that the insulin-like activity in urine of obese subjects is more closely associated with albumin than with unmodified insulin.