Chick-erythrocyte nucleus reactivation in heterokaryons: suppression by inhibitors of proteolytic enzymes

Reactivation of chick-erythrocyte nuclei in heterokaryons (obtained by Sendai virus-induced fusion of chick erythrocytes with HeLa cells) is suppressed by specific inhibitors of trypsin and trypsin-like enzymes. N-alpha-tosyl-L-lysyl-chloromethane and N-alpha-tosyl-L-arginine methylester inhibit erythrocyte nuclear enlargement and suppress RNA and DNA synthesis in nuclei of erythrocytes and HeLa cells in heterokaryons at concentrations that only minimally influence individual HeLa cells or HeLa homokaryons. Although other unknown mechanisms of action cannot be formally excluded, the data are interpreted as fitting best with an intracellular site of action of the protease inhibitors studied, and as suggesting a role for cellular proteases in reactivation of chick-erythrocyte nuclei in heterokaryons.

Uptake of tritium-labeled adenosine triphosphate by the cytoplasm of fixed interstitial cells from rat testes

The cytoplasm of histologically fixed interstitial cells of rat testes becomes heavily labeled after incubation in the presence of tritium-labeled adenosine triphosphate. The phenomenon shows a high degree of specificity; none of the other eight types of cells studied (five of nontesticular origin) exhibits significant labeling under the same conditions. The cell labeling seems to be nonenzymatic in character; specific macromolecules associated with retention of the label have not been identified. Label retained by the cytoplasm of interstitial cells withstands: (a) prolonged washings in cold 5% trichloroacetic acid; (b) washings in a solution of high ionic strength; (c) repeated washings with alcohol and with water; (d) heating to 100°C; and (e) treatment with enzymes hydrolyzing nucleic acids (deoxyribonuclease I, ribonuclease A, ribonuclease T2, micrococcal nuclease and phosphodiesterase).

Modification of the gelatin substrate procedure for demonstration of acrosomal proteolytic activity

In situ proteolytic activity in the heads of sperm of seven mammalian species has been demonstrated using autoradiographic film as a gelatin substrate. The film is first exposed and processed and then coated with the sperm sample. Proteolytic activity is monitored by following the appearance of "halos," which are areas of gelatin digestion and are found to surround the heads of reacting sperm. The proteolytic factor appears to be released from the acrosome and may be the protease with trypsin-like activity that has been found associated with the acrosome in biochemical studies. l-Chloro-3-tosylamido-7-amino-2-heptanone and diisopropyl fluorophosphate, both of which inhibit trypsin activity, apparently interact with a substance released from the acrosome but do not interfere with the formation of halos. Sperm treated with trichloroacetic acid, urea or formalin do not form halos.

Quantitative studies on enzymes in structures in striated muscles by labeled inhibitor methods. I. The number of acetylcholinesterase molecules and of other DFP-reactive sites at motor endplates, measured by radioautography

Di-isopropylfluorophosphate (DFP) labeled with phosphorus-32 was applied to fragments of the diaphragm and sternomastoid muscles of the mouse, in conditions in which it saturated all available sites at the motor endplates. After adequate washing and exchange with unlabeled DFP, single endplates were obtained by microdissection and their radioactivity was found by beta track radioautography. The number of sites phosphorylated by DFP-(32)P per endplate was relatively constant for each muscle: in the sternomastoid, about 9 x 10(7) sites per endplate, in the diaphragm, about 3 x 10(7). Reaction with DFP-(32)P was abolished by prior treatment with unlabeled DFP. Labeling was unaffected by prior fixation in formaldehyde, but was inversely proportional to the time of incubation in the Koelle staining medium, when this preceded labeling. The contribution of acetylcholinesterase (AChase) to this total number of DFP-reactive sites was determined by three methods. The first involved reactivation of the phosphorylated AChase by pyridine-2-aldoxime methiodide (2-PAM), in conditions in which the reactivation of other enzymes would be insignificant. The other two methods involved protection of the active centers of AChase from phosphorylation by labeled DFP by use of 284C51, an inhibitor highly specific for this enzyme, or by use of eserine. Each of these methods indicated that about 35% of the DFP-reactive sites at endplates of the sternomastoid and diaphragm are AChase. The mean number of AChase molecules was thus found to be 3.1 x 10(7) and 1.1 x 10(7)per endplate in sternomastoid and diaphragm, respectively. No significant reaction of labeled DFP with muscle and nerve was observed. Mast cells in the muscle had a concentration of DFP-reactive sites far higher than the endplates.

Quantitative analysis of the esterases in rat megakaryocytes by a radio-isotope cytochemical technique

Megakaryocytes from bone marrow of immature rats have been treated with 3H-DFP, and the grain density over them measured in autoradiographs. The uptake of labeled DFP is reduced by one-third by eserine and by the AChase inhibitor 284C51, and by reactivation with pyridine-2-aldoxime. It is concluded that one-third of the DFP taken up by megakaryocytes represents binding to true AChase. The other esterases present include no significant amount of pseudocholinesterase.

Autoradiography with tritiated methotrexate and the cellular distribution of folate reductase

Bound methotrexate has been revealed by an autoradiographic procedure, presumed to introduce a method for cytochemical study of folate reductase. Preferential localization is seen in kidney proximal tubules, intestinal epithelium, and nuclei of parenchymal liver cells in mice. The extremely firm binding and prolonged retention of this drug should render it suitable as an inert label for the autoradiographic study of cell migrations and lifetimes.