Substructure of membranes in cultivated chick embryo fibroblasts

Summary Electron microscope examination of the plasma membrane of chick embryo fibroblasts cultured in vitro revealed the presence of a single osmiophilic layer about 90 Å thick and a substructure composed of ovoid sub-units associated with an amorphous component. These ovoid sub-units measured approximately 112 Å along the major axis and 75 Å along the minor axis and were composed of a central core, approximately 30 Å by 60 Å, surrounded by a peripheral component.Examination of other membranous components of these cells revealed a similar ovoid subunit structure in a single layered membrane. Differences in thickness and in the sizes of ovoid sub-units were seen in these membranes. The ergastoplasmic membranes, the outer nuclear membranes, the outer mitochondrial and the Golgi membranes were found to be the thinnest.These varied in thickness from approximately 75 Å to 80 Å. The thickest membranes seen were the inner nuclear membranes. These were approximately 100 Å thick. The dimensions of the ovoid sub-units corresponded with differences in the thickness of the various membranes. These findings support the concept of a particulate substructure of cell membranes.This work was aided by Research Grant PH 5593 from the National Science Foundation. Some of the equipment used was purchased with funds from the National Institutes of Health Grant 2TI GM 326. I wish to thank Dr. Robert M. Dougherty from the Department of Microbiology who grew and supplied me with the chick embryo fibroblast cultures used in these studies, and Mrs. Ursula Feller fer her technical assistance.     

DNA ploidy of human breast cancer

Ploidy was determined on 663 resectable primary tumors from untreated patients. Nuclei obtained by mechanical disaggregation of frozen tissue were stained with propidium iodide and analysed in a FACS IV. Aneuploidy was detected in 73% of cases. It was not significantly related to nodal involvement or tumor size, although the highest frequencies were observed in large tumors (88%) or with more than 10 positive nodes (77%). Aneuploidy was more frequently observed in ductal infiltrating (81%) than in lobular histology and in tumors lacking both progesterone and estrogen receptors (85%). Analysis of ploidy in primary and synchronous lymph node metastases from the same patient showed a high agreement rate (90%) of DNA patterns simply defined as diploid or aneuploid. However, differences in DNA stemlines and DNA indices between the two synchronous lesions from the same patient were a rather frequent event.     

Effect of protons on the amidase activity of human alpha-thrombin. Analysis in terms of a general linkage scheme

The amidase activity of human alpha-thrombin has been studied in the pH range 5.5 to 10, and at four different chloride concentrations from 5 mM to 1 M. The Michaelis-Menten constant, Km, shows a bell-shaped dependence over the pH range studied, with a minimum around pH 8. The pH dependence of the catalytic constant, kcat, shows multiple inflection points especially at low (less than 0.1 M) chloride concentrations, thereby implicating the existence of multiple catalytic forms of the enzyme. A general linkage scheme is proposed for the analysis of the effect of protons on thrombin amidase activity, and experimental data have globally been analysed over the entire pH range in terms of such a scheme. Four proton-linked ionizable groups seem to be involved in the control of thrombin amidase activity. Two of these groups change their pK value upon substrate binding to the enzyme and account for the pH dependence of Km. All four groups control the catalytic activity of the enzyme which decreases with increasing protonation. Chloride has little effect on Km, while kcat changes significantly at pH less than 8. This effect is due to an increased enzymatic activity of the highly protonated intermediates at high chloride concentrations, as well as to the pK shift of two proton-linked ionizable groups.