Reversal of X-inactivation in female mouse somatic cells hybridized with murine teratocarcinoma stem cells in vitro

A series of near-diploid embryonal carcinoma-like hybrid cells were obtained from polyethylene glycol mediated cell fusion between murine embryonal carcinoma cells (PSA-6TG1 or OTF9-63) having one X chromosome and thymocytes or bone marrow cells from female mice carrying Cattanach's or Searle's translocation. Prior to fusion with EC cells the somatic cells are presumed to contain only one active X chromosome. Following hybrid formation, the chronology of X chromosome replication and the expression of X-linked gene Pgk-1 indicated that all X chromosomes contributed by both parents were active in these hybrids. Experiments were performed to rule out the possibility that the hybrids were formed by fusion of EC cells with rare somatic cells in which both X chromosomes were active. Taken together the data indicate that within four days of fusion there is reactivation of the entire inactive X chromosome.     

Amino acid sequence of the active site of human pseudocholinesterase

The usualE ₁ ^u and atypicalE ₁ ^a human pseudocholinesterases (acylocholine acylhydrolase, EC 3.1.1.8) were purified to homogeneity. The active-site serine residue was conjugated with diisopropyl fluorophosphate and digested with trypsin. The tryptic peptide containing the active site was isolated by gel filtration followed by two-dimensional paper chromatography and electrophoresis. The amino acid sequence of the active site peptide obtained from the usualE ₁ ^u enzyme was found to be Gly-Glu-Ser-Ala-Gly-Ala-Ser-Ala-Val-Ser-Leu. A remarkable structural homology exists between the human and the horse enzymes in their active sites. From the difference in electrophoretic mobility of the active-site peptides obtained from the usual and atypical enzymes, the probable structure of the atypical human enzyme was deduced as Gly-His-Ser-Ala-Gly-Ala-Ser-Ala-Val-Ser-Leu.     

Glucose catabolism during aging and differentiation in hypocotyls ofPhaseolus mungo seedlings

Changes in activities of the glycolytic and pentose phosphate (PP) pathways in glucose catabolism in various parts of the hypocotyls obtained from 4-day-old etiolatedPhaseolus mungo seedlings were investigated by measuring the inhibition rates of respiration by iodoacetate and malonate, and the release of¹⁴CO₂ from [1-¹⁴C]- and [6-¹⁴C]glucose. The relative activity of the PP pathway in glucose catabolism was higher in the immature part (Part I) and the aged part (Part V) of the hypocotyls than in the intermediary one (Part III), while the activity of the glycolytic pathway decreased with aging. On a fresh weight basis, the enzyme activities of the glycolytic and PP pathways were higher in Part I than in Parts III and V. On a protein content basis, however, activities of the enzymes of the PP pathway increased with aging and differentiation of the hypocotyls whereas those of the glycolytic pathway decreased. Levels of nicotinamide adenine nucleotides were found to be in the following order: Part I>Part III> Part V for NAD⁺+NADH; Part I>Part V>Part III for NADP⁺+NADPH. The stimulative effect of methylene blue on decreasing the C₆/C₁ ratio was greater in Part III than in Part I, and No effect was observed in Part V. These data suggest that a decrease in the activity of the glycolytic pathway with aging and differentiation may be due to the decreasing glycolytic enzyme activities and NAD(H) content. The higher activity of the PP pathway in the immature part is attributable to larger amounts of NADP(H) and enzymes of the PP pathway. The greater contribution of the PP pathway to glucose catabolism in the aged part than in the intermediary part seems to results from a more active turnover of NADP and the relatively higher activity of the enzymes of the PP pathway than those of the glycolytic pathway.     

The nucleotide sequency of tRNA Gly from yeast

Analysis of the factor for proximity and orientation is given for cyclopentadiene dimerization and for the general case of more complex biological molecules. Using either a probability or a statistical mechanical approach, the same ratios are obtained. The proximity effect factor is found to be about $\text{55}\text{n}{}_{\mathrm{n}}$ per reacting pair of molecules which show no net attraction or repulsion. The use of translational entropy without inclusion of a rotational entropy term gives a misleading value for this proximity factor. The calculations support the argument that orientation factors can play a large role in the catalytic power of enzymes.