The use of fluorescent molecules as probes of protein conformation is recognized as a technique which provides very specific information and has been applied, in recent years, to the study of the role of tropomyosin (TM) in the regulation of contractile processes. The isolation and sequencing of TM from horse blood platelets (P-TM) has shown it to be different from muscle TM, especially near the NH₂-and COOH-termini. These differences have been suggested to weaken end-to-end interaction of P-TM molecules. TM's are two chain coiled coils and P-TM has cysteine residues at the penultimate COOH-terminus position of adjacent chains. These can be labelled with sulfhydryl-specific fluorescent probes that reflect conformational changes in that region of the molecule via changes in their emission characteristics. The results of experiments on both pyrene (Py) (40) and acrylodan (AD) labelled P-TM show that there is a preferred interaction of the COOH-terminus of P-TM with the NH₂-terminus of cardiac TM over that with the NH₂-terminus of P-TM. This indicates that the altered NH₂-terminus of P-TM, with respect to muscle TM, is responsible for the relative loss of polymerizability of P-TM at low salt concentration. Addition of actin to the Py-P-TM (40) and AD-P-TM species showed changes in emission characteristics indicative of binding to the F-actin filaments, suggesting that the presence of the probes had not affected the function of the P-TM adversely. However, the presence of pyrenes at the COOH-terminus seemed to reduce further the ability of P-TM to self-polymerize. Thermal denaturation of AD-P-TM, AD-C-TM and AD-labelled truncated P-TM followed by fluorescence polarization suggested that, contrary to the theory of Skolnick and Holtzer on the stability of two chain coiled coils, the region towards the COOH-terminus is among the last to lose its helical character. / Science, Faculty of / Chemistry, Department of / Graduate

Using nuclei isolated from less than 0.2 g tissue or 107 cells, a method is presented for the quantitative determination of amounts of DNA per cell at the picogram level. This technique is based on the enhanced fluorescence of 4′,6-diamidino-2-phenylindole (DAPI) when it binds to DNA. A rapid, one-step nuclear isolation and DNA staining procedure is used to prepare tissue samples for flow cytometric analysis. Frozen tissues give results comparable to those for fresh tissue. Both chicken and trout erythrocyte nuclei were used as reference standards in the determination of amounts of DNA per diploid cell for several mammals and Amazon molly fish. The consistent values obtained for different tissues from the same organism show the accuracy of this method for DNA measurement.

A case is presented in which flow cytometric and cytogenetic analysis was done on a biopsy from a highly anaplastic metastatic adenocarcinoma. Flow cytometric analysis of DNA content failed to show a significant population of aneuploid cells. However, histologic examination revealed a substantial number of tumor cells, and cytogenetic analysis produced chromosome counts ranging from 20 to 144.