Relationship between cell density and prolidase activity in human skin fibroblasts: effects of ascorbate and fructose

To evaluate the influence of cell density on the activity of fibroblast prolidase (EC 3.4.13.9), we determined this activity in sparse and dense cultures. We also investigated, the effects of different concentrations of β-d(?) fructose and l(+) ascorbate, which both increased cell density at confluency. For a fructose concentration of 25 mM, we observed that in the absence of glucose, intracellular total proteins increased 1.5-fold and prolidase specific activity, 1.8-fold. For ascorbate, a broad optimum concentration was found (range 0.01 – 0.50 mM). Addition to cultures of 0.1 mM ascorbate increased total proteins 1.4-fold, and doubled prolidase activity. This investigation was prompted by our previous results [J. Metab. Dis. 1983, 6, 27–31], confirmed here, and suggesting that increased prolidase activity at confluency was due to a rise in cell density.     

Alpha-DNA. IV: Alpha-anomeric and beta-anomeric tetrathymidylates covalently linked to intercalating oxazolopyridocarbazole. Synthesis, physicochemical properties and poly (rA) binding

A new set of molecules made of an intercalating agent (oxazolopyridocarbazole, OPC) covalently linked through a polymethylene chain of various length to the 3' end of alpha-anomeric or beta-anomeric tetradeoxynucleotides (alpha- or beta-T4) have been synthesized. The beta-thymidylate modified compound (beta-T4C5OPC) is able to interact with the complementary sequence, beta-poly (rA); this interaction is strongly stabilized compared to the parent compound, beta-oligo(dT)4 and is specific for poly (rA). The molecule synthesized from the unnatural alpha-anomer, alpha-T4C5OPC, is also able to interact with poly (rA) leading to the formation of an alpha-beta hybrid stabilized by the energy provided by the OPC moiety. The stoechiometry of the binding reaction shows that an A-T pairing occurs in the alpha-beta heterohybrids. Tm studies reveal that the alpha-beta heterohybrids are more stable than their beta-beta counterparts.     

Creatine kinase activity of urinary bladder and skeletal muscle from control and streptozotocin-diabetic rats

The urinary bladder depends on intracellular ATP for the support of a number of essential intracellular processes including contraction. The concentration of ATP is maintained constant primarily via the rapid transfer of a phosphate from creatine phosphate (CP) to ADP catalyzed by the enzyme creatine kinase (CK). Since muscular pathologies associated with diabetes are in part related to intracellular alterations in metabolism, we have characterized the CK activity in both skeletal muscle and urinary bladder from control and streptozotocin-diabetic rats.The following is a summary of the results: 1) Bladder tissue from control rats showed linear kinetics with a V_max = 390 nmoles/mg protein/min, and a K_m = 275 µM. 2) Urinary bladder tissue isolated from diabetic rats displayed biphasic kinetics with V_max = 65 and 324 nmoles/mg protein/min, and K_m's = 10 µM and 190 µM respectively. 3) Skeletal muscle isolated from control rats showed linear kinetics with an approximate V_max of 800 nmoles/mg protein/min and a K_m of 280 µM CP. 4) Homogenates of skeletal muscle from diabetic rats showed complex kinetics not separable into distict component forms. 5) The K_m for ADP for both skeletal muscle and bladder was approximately 10 µM.These studies demonstrate that whereas bladders isolated from both control and diabetic rats possess a low-affinity isomer(s) of CK with similar maximum enzymatic activity, there is a high affinity isomer present within the urinary bladder muscle of diabetic rats that is not present in bladder tissue isolated from control rats. Skeletal muscle isolated from both diabetic and control rats exhibited a maximal activity 2 to 3 times higher than that of the bladder.     

The compositional distribution of coding sequences and DNA molecules in humans and murids

Summary The compositional distributions of coding sequences and DNA molecules (in the 50-100-kb range) are remarkably narrower in murids (rat and mouse) compared to humans (as well as to all other mammals explored so far). In murids, both distributions begin at higher and end at lower GC values. A comparison of homologous coding sequences from murids and humans revealed that their different compositional distributions are due to differences in GC levels in all three codon positions, particularly of genes located at both ends of the distribution. In turn, these differences are responsible for differences in both codon usage and amino acids. When GC levels at first+second codon positions and third codon positions, respectively, of murid genes are plotted against corresponding GC levels of homologous human genes, linear relationships (with very high correlation coefficients and slopes of about 0.78 and 0.60, respectively) are found. This indicates a conservation of the order of GC levels in homologous genes from humans and murids. (The same comparison for mouse and rat genes indicates a conservation of GC levels of homologous genes.) A similar linear relationship was observed when plotting GC levels of corresponding DNA fractions (as obtained by density gradient centrifugation in the presence of a sequence-specific ligand) from mouse and human. These findings indicate that orderly compositional changes affecting not only coding sequences but also noncoding sequences took place since the divergence of murids. Such directional fixations of mutations point to the existence of selective pressures affecting the genome as a whole.     

Prochlorococcus marinus nov. gen. nov. sp.: an oxyphototrophic marine prokaryote containing divinyl chlorophyll a and b

Several years ago, prochlorophyte picoplankton were discovered in the N. Atlantic. They have since been found to be abundant within the euphotic zone of the world's tropical and temperate oceans. The cells are extremely small, lack phycobiliproteins, and contain divinyl chlorophyll a and b as their primary photosynthetic pigments. Phylogenies constructed from DNA sequence data indicate that these cells are more closely related to a cluster of marine cyanobacteria than to their prochlorophyte relatives Prochlorothrix and Prochloron. Several strains of this organism have recently been brought into culture, and herewith are given the name Prochlorococcus marinus.