Synchronization of 9L rat brain tumor cells by centrifugal elutriation

Asynchronous 9L cells were separated into relatively homogeneously-sized populations using centrifugal elutriation with both a conventional collection method and a long collection method. A substantial increase in the homogeneity of the volume distributions and in the degree of synchrony of the separated fractions was obtained using the long collection method. Autoradiographic data indicated that fractions containing ≥97% G₁ cells, ≥80% S cells, and 70–75% G₂ cells could be routinely recovered with this procedure. Recovery in these fractions varied from 5 to 8% of the total number of cells elutriated. The colony forming efficiency (CFE) of cells from fractions representing each phase of the cell cycle was a constant 60–70%, which was comparable to the 60–80% usually found for asynchronous 9L cells. The percentage of cells in the G₁, S, and G₂ phases in the elutriated fractions was more accurately determined from the volume distribution than from computer fits of the DNA histogram obtained from flow cytometry. In general, the degree of synchrony was related to the coefficient of variation (CV) of the volume distributions of the elutriated fractions. The CV was about 14% for all elutriated fractions. When the ≥97% G₁ population was allowed to progress to S and G₂, the CVs were about 17 and 20.2%, respectively. Thus, the best nonperturbing method for obtaining synchronous 9L cells in the S or G₂ phases was direct elutriation with the long collection method.     

Creatine phosphate inhibition of adenylate deaminase is mainly due to pyrophosphate.

Inhibition of rat skeletal muscle adenylate deaminase by creatine phosphate reported previously is due to inorganic pyrophosphate present as a contaminant in commercial preparations of creatine phosphate. This conclusion is based on the following evidence: a compound that inhibits adenylate deaminase can be separated from commercially prepared creatine phosphate by ion exchange chromatography; the inhibition by "creatine phosphate" and by the separated inhibitory compound is relieved by treatment with inorganic pyrophosphatase; inhibition by inorganic pyrophosphate is similar to that produced by unpurified creatine phosphate; and pyrophosphate is present in commercially available creatine phosphate in amounts sufficient to account for the inhibition. Some commercial preparations of creatine phosphate contain much less pyrophosphate than others; these preparations are only weakly inhibitory. Inorganic triphosphate is a more powerful inhibitor of the enzyme than pyrophosphate; it may also be present as a contaminant in creatine phosphate.     

Requirement for negatively charged dispersions of phospholipids for interaction with lipid-depleted adenosine triphosphatase.

The basis of the requirement for a net negative charge on phospholipid dispersions able to re-activate lipid-depleted (Na++K+)-dependent adenosine triphosphatase was studied. The origin and density of the charge in phospholipid dispersions were varied before interaction with the adenosine triphosphatase protein, and the charge density on restored phospholipid-adenosine triphosphatase complexes was changed after interaction. The results indicated that: (a) re-activation requires a lamellar arrangement of the lipid molecules with sufficient density of negative charge, but not necessarily negatively charged phospholipid molecules; (b) the net charge appears to be necessary for the correct interaction between the enzyme protein and the phospholipids, although the amount of phospholipid that binds to the protein is also a function of the nature of the acyl chains; (c) it is not possible on the basis of these findings and those in the literature to decide unequivocally if the charge is also required for the enzyme reaction itself. The possible relevance of the findings to the situation in vivo is discussed in terms of the charge being concerned only with lipid-protein interaction.     

Ultrastructural and chemical distinction of melanins formed by Verticillium dahliae from (+)-scytalone, 1,8-dihydroxynaphthalene, catechol, and L-3,4-dihydroxyphenylalanine

Microsclerotia of three melanin-deficient mutants of Verticillium dahliae formed malanin from (+)-scytalone, 1,8-dihydroxynaphthalene, catechol, and L-3,4-dihydroxyphenylalanine. The melanins formed from (+)-scytalone or 1,8-dihydroxynaphthalene resembled wild-type melanin chemically and ultrastructurally, whereas the melanins formed from catechol and L-3,4-dihydroxyphenlalanine were different. This suggests that scytalone and 1,8-dihydroxynaphthalene but no catechol or L-3,4-dihydroxyphenylalanine are natural intermediates of melanin biosynthesis in V. dahliae.     

Localization of Drosophila nasutoides satellite DNAs in metaphase chromosomes

Metaphase chromosomes of D. nasutoides were hybridized situ with ³H-cRNA synthesized from the four satellites which make up 50–60% of the total DNA of this species. All four satellites were localized in the large, metacentric, heterochromatic chromosome four. They did not, however, appear to hybridize to centromeric or other constitutive heterochromatin, nor did they, with the exception of satellite I, seem to hybridize in the specific regions of chromosome four which, on the basis of C, Q, and H banding and AT contents, were predicted to contain some of these satellites. —Comparison of grain patterns with the results of fluorescent staining indicated that satellite-bearing heterochromatin was not always associated with other fractions of constitutive heterochromatin in interphase nuclei and was, at least partially, decondensed in some larger nuclei.     

Location of the sequences coding for capsid proteins VP1 and VP2 on polyoma virus DNA.

The 19S and 16S polyoma virus late mRNAs have been separated on sucrose-formamide density gradients and translated in vitro. The 16S RNA codes only for polyoma capsid protein VP1, while the 19S RNA codes in addition for capsid protein VP2. Since the 19S and 16S species have been previously mapped on the viral genome, these results allow us to deduce the location of the sequences coding for VP1 and VP2. Comparison of the chain lengths of the capsid proteins with the size of the viral mRNAs coding for them suggests that VP1 and VP2 are entirely virus-coded. Purified polyoma 19S RNA directs the synthesis of very little VP1 in vitro, although it contains all the sequences required to code for the protein. The initiation site for VP1 synthesis which is located at an internal position on the messenger is probably inactive either because it is inaccessible or because it lacks an adjacent "capped" 5' terminus. Similar inactive internal initiation sites have been reported for other eucarotic viral mRNAs (for example, Semliki forest virus, Brome mosaic virus, and tobacco mosaic virus), suggesting that while eucaryotic mRNAs may have more than one initiation site for protein synthesis, only those sites nearer the 5' terminus of the mRNA are active.     

Insulin stimulation of heart glycogen synthase D phosphatase (protein phosphatase).

Insulin rapidly produced an increase in per cent of total heart glycogen synthase in the I form in fed rats. In fasted rats the response was diminished and delayed. In diabetic animals there was no response over the 15-min time period studied. Since synthase phosphatase activity is necessary for synthase D to I conversion, the phosphatase activity was determined in extracts from these groups of animals. In the fasted and diabetic rats phosphatase activity was less than one-half of that in fed animals. Administration of insulin to fasting animals increased synthase phosphatase activity to a level approaching that of fed animals by 15 min. In diabetic animals insulin also stimulated an increase in synthase phosphatase activity but 30 min were required for full activation. Insulin had no effect in normal fed animals. Insulin activation of synthase phosphatase activity in heart extracts from fasted animals was still present after Sephadex G-25 chromatography and ammonium sulfate precipitation. Thus insulin had induced a stable modification of the phosphatase itself or of its substrate synthase D rendering the latter a more favorable substrate for the reaction. A difference in sensitivity of the reaction to glycogen inhibition was present between fed and fasted animals. Increasing concentrations of glycogen had only a slight inhibitory effect in extracts from fed animals but considerably reduced activity in extracts from fasted animals. Insulin administration reduced the sensitivity of the phosphatase reaction to glycogen inhibition. This could explain, at least in part, the increased phosphatase activity noted in the insulin-treated, fasted rats since glycogen was routinely added to the homogenizing buffer.     

The effects of the trinitrophenylation of the amino groups of glucagon on its conformational properties and on its ability to activate rat liver adenylyl cyclase.

Trinitrophenyl groups have been specifically introduced into the alpha- and/or the epsilon-NH2 groups of glucagon by reaction with trinitrobenzenesulfonic acid. Introduction of this group into the epsilon-NH2 position of the hormone leads to an apparant increase in the helical content as measured by circular dichroism, while substitution on the alpha-NH2 position causes little change in this property. The usefulness of the trinitrophenyl group for the study of intramolecular singlet excitation transfer from tryptophan is suggested. The pK and reactivity of the amino groups, as measured by the pH dependence of the rate of reaction with trinitrobenzenesulfonic acid, showed that the two amino groups of glucagon have similar properties to those of small model peptides. The trinitrophenyl-glucagon derivatives have little or no activity in stimulating adenylyl cylase of rat liver. By comparison with previously reported results, this demonstrates that the effect of chemical modifications of the amino group on the biological activity of glucagon depends critically on the group which is introduced.