Increased proline transport resulting from growth of normal and Kirsten sarcoma virus-transformed BALB 3T3 cells in the presence of N(6), O(2')-dibutyryl cyclic adenosine 3',5'-monophosphate.

Proline transport in Kirsten sarcoma virus-transformed BALB 3T3 (Ki-3T3) cells was increased approximately twofold by 0.5 mm dibutyryl cAMP (dbcAMP), and the increase was observed whether transport was assayed in the presence or absence of cycloheximide. Two days of exposure to the analog was required for maximum stimulation. Increased proline transport contributed almost entirely to the increased incorporation of [¹⁴C]proline into noncollagen protein but for only 13% of the increased incorporation into collagen of dbcAMP-treated Ki-3T3 cells. Proline transport was further characterized using an assay system containing 0.1 mm cycloheximide, which did not affect transport over a 30-min period. The K_m for proline was decreased from 6.5 to 3.4 mm by dbcAMP treatment of Ki-3T3. Proline transport in Ki-3T3 proceeds almost entirely via the A system, and the effect of dbcAMP appears to be on this system specifically since glycine and glutamine transport, which are heterogeneous, were not affected but transport of N-methylaminoisobutyrate, a specific A system substrate, was increased by dbcAMP treatment. Although 0.5 mm butyrate increased proline transport in Ki-3T3 cells to a similar degree as dbcAMP, the effect of the latter appeared related to its action as a cAMP analog since N⁶-monobutyryl cAMP, having a stable butyryl group, and 8-bromo-cAMP also increased proline transport while dbcGMP did not. The rate of proline transport in normal BALB 3T3 cells was only 30–40% lower than that of Ki-3T3 cells at various growth stages, and dbcAMP and 8-bromo-cAMP treatment also increased proline transport in the normal cells. The results of these studies suggest that dbcAMP and other cAMP analogs induce the synthesis of an altered component of the A system for amino acid transport and that the effect of these compounds is unrelated to the effect of transformation on proline transport.     

The spread of somatosensory-evoked potentials within the nervous system

Four thalamic and cortical recordings were carried out in 5 patients. The thalamic-evoked potentials were typical and revealed a triphasic complex, but their latencies showed a relatively high standard deviation. They could be divided into two groups according to their latencies, both of which had low SD. These data suggested that there could be two types of latency of thalamic SEP, because the 4 patients' body sizes were very similar. More detailed surface, cortical and depth recordings are needed to resolve these questions.     

Modification by azocombination of the catalytic properties of ribonucleases

Using pancreatic RNAase and RNAase from Act. rimosus as models, the effect of modification by azocombination on the catalytic properties of enzymes were studied. It was shown that RNAases binding to soluble dextran did not cause any significant changes in their major catalytic properties, when polymeric RNA was used as a substrate. At the same time, the physico-chemical properties of the modified enzymes may result in changes in the catalytic properties in a reaction with low molecular weight substrates. Evidence for this observation can be obtained from the increase in the synthetic activity of modified pancreatic RNAase as compared to the hydrolase activity in the dinucleotide synthesis reaction.     

Isolation of serum chylomicrons prior to density gradient ultracentrifugation of other serum lipoprotein classes

A method for the removal of serum chylomicrons before density gradient ultracentrifugation of the other serum lipoproteins using an SW 41 swinging bucket rotor is presented. In a preliminary spin, the chylomicrons with an Sf greater than 400 X 10(-13) s float to the top of the gradient, whereas the other lipoproteins are retained in the infranatant fraction. After removal of the chylomicrons, the other serum lipoproteins are subsequently fractionated by isopycnic density gradient ultracentrifugation. Analysis of the separated lipoprotein fractions suggested that this procedure permits isolation of a chylomicron fraction consisting solely of chylomicrons but that the very low density lipoprotein fraction subsequently isolated also contains chylomicrons or chylomicron remnants with an Sf less than 400 X 10(-13) s, and that there is considerable overlap in flotation rate and particle size of very low density lipoproteins and chylomicrons.     

Characterization of messenger RNA from epimastigotes and metacyclic trypomastigotes of Trypanosoma cruzi

The cell-free translation products of polyribosomal and post-polyribosomal mRNAs from the non-infective epimastigotes and the infective metacyclic trypomastigotes of the parasitic protozoan Trypanosoma cruzi were compared by two-dimensional polyacrylamide gel electrophoresis. The result show that although many polypeptides are conserved, quantitative and qualitative differences are observed between both differentiation stages. The results also indicate the existence of post-polyribosomal mRNAs in equilibrium with polyribosomal counterparts. The immunoprecipitation of the in vitro synthesized polypeptides with chagasic human serum and the serum raised against an 85-kDa glycoprotein (P2-WGA), potentially involved in the process of T. cruzi penetration into mammalian cells, shows that while the chagasic serum recognizes the same 72-kDa, 68-kDa and 46-kDa polypeptides in both differentiation stages, the anti-P2-WGA serum immunoprecipitates a single 48-kDa polypeptide from in vitro translation products of metacyclic trypomastigotes.     

The Expression of Race-Specific Resistance of Wheat Seedlings to Puccinia recondita

A range of wheat cultivars with resistance factors effective against Puccinia recondita f. sp. tritici was studied to investigate the mode of action and expression of resistance at first and third seedling leaf stages. In most cultivars, resistance to isolate 74/2 resulted in extremely low levels of infection, apparently linked with a predominantly hypersensitive response by the host. In seedlings of cultivars Mans Fundin and Sterna, however, race-specific resistance was expressed as increased pathogen latent period and intermediate infection levels.