Age changes in the H1 group of histones from rat liver.

Histones were obtained from young and old rat livers by extracting them in 0.25 N HCl. They were fractionated on 15% acid urea polyacrylamide gels containing 6.25 M urea and the changes in the ratio of the major histone fractions as a function of age were calculated. Data presented show a significant increase in the amount of H1 degree fraction in the liver of old rats as compared to young rats. This data is discussed and the possible involvement of H1 degree fraction in an increased resistance of old rat liver chromatin to micrococcal nuclease digestion of linker DNA is suggested. Finally, in connection with this increased resistance, some possible consequences in chromatin structure are discussed.

A simple spectrophotometric method for the measurement of ribonuclease activity in biological fluids.

We have developed a rapid and sensitive method for detecting ribonuclease (RNAase). The method makes use of a RNA-Pyronine Y complex which has a different absorption spectrum from that of Pyronine Y alone. When the RNA is hydrolyzed by RNAase, the spectrum of the complex changes to that of unbound Pyronine Y. The resultant decrease in absorbance at 572 nm is linear for final RNAase concentrations ranging from 2 to 45 ng/ml. Optimal assay conditions were 11.5 micrograms/ml Pyronine Y, 0.56 mg/ml RNA, 80 mumol/ml Tris-HCl buffer, pH 7.8, and 2-45 ng/ml RNAase. The effect of complex concentration, pH, molarity and temperature upon the rate of the reaction were determined. The assay is applicable to crude cell-free extracts.

Ultrastructure of the liver cells in Salamandra salamandra (L.) in the end of Winter.

Following hibernation, most salamander liver cells undergo alterations. The liver cells containing the structure of their active period present a normal nucleus, glycogen granules disseminated throughout the entire cytoplasm and granular mitochondria with several peripheral cristae. Most cells, however, possess altered mitochondria, transformed into electron-dense masses, or clear vesicles with the possibility of digesting the ambient organelles. Other cells have clear vacuoles with similar digestive possibilities. The endoplasmic reticulum is poorly represented in the liver cells that have suffered advanced alteration. The nucleus of these cells is homogeneously granular. The sytoplasm is populated by electron-dense bodies and lipid vacuoles. The nucleolemma and plasmalemma are thickened. The pigmented cells, altered concomitantly with the liver cells, contain granular aggregates. Some of the pigmented cells exhibit electron-clear formations similar to the reflecting platelets of the iridocytes of the integument of lower vertebrates.