Demonstration and ontogenesis in the rat of a serum protein analogous to human thyroxine binding globulin

It has been reported evidence based on equilibrium binding, electrophoretic, immunoelectrophoretic studies, that the rat possesses a major high affinity thyroid hormone binding protein, with an electrophoretic mobility and binding properties similar to those of the human thyroxine binding globulin (TBG). It is shown that in the sera of postnatal developing animals, between 3 and 21 days, the thyroxine (T4) and the triiodothyronine (T3) binding activities increase up to 10 times over adult or foetal levels, due to a high transient post-natal surge of the rat TBG. In the adult serum, the TBG persists in decreased amounts: it then yields the predominant role as T4 carrier to the thyroid binding prealbumin (TBPA), but retains the major role as binder of T3, i.e. of the biologically active thyroid hormone.     

The lack of effect of pentoxifylline on random skin flap survival

The effects of pentoxifylline on skin flap survival were studied in rabbits. A total of 40 rabbits had caudally based single-pedicle flaps measuring 4 x 14 cm raised on the mid dorsum of each animal. Twenty of these rabbits were given intraperitoneal injections of pentoxifylline in doses of 24 mg/kg per day beginning 48 hours prior to flap construction and continued daily for 7 days postoperatively. The remaining 20 control rabbits received intraperitoneal injections of saline in equal volumes as the experimental groups. At the end of 7 days, viable flap length was visually inspected and measured in all 40 rabbits. There was no significant difference in skin flap viability in rabbits treated with pentoxifylline compared to the control group.     

Purification and properties of 2-aminoadipate: 2-oxoglutarate aminotransferase from bovine kidney.

Escherichia coli endonuclease IV hydrolyses the C(3')-O-P bond 5' to a 3'-terminal base-free deoxyribose. It also hydrolyses the C(3')-O-P bond 5' to a 3'-terminal base-free 2',3'-unsaturated sugar produced by nicking 3' to an AP (apurinic or apyrimidinic) site by beta-elimination; this explains why the unproductive end produced by beta-elimination is converted by the enzyme into a 3'-OH end able to prime DNA synthesis. The action of E. coli endonuclease IV on an internal AP site is more complex: in a first step the C(3')-O-P bond 5' to the AP site is hydrolysed, but in a second step the 5'-terminal base-free deoxyribose 5'-phosphate is lost. This loss is due to a spontaneous beta-elimination reaction in which the enzyme plays no role. The extreme lability of the C(3')-O-P bond 3' to a 5'-terminal AP site contrasts with the relative stability of the same bond 3' to an internal AP site; in the absence of beta-elimination catalysts, at 37 degrees C the half-life of the former is about 2 h and that of the latter 200 h. The extreme lability of a 5'-terminal AP site means that, after nicking 5' to an AP site with an AP endonuclease, in principle no 5'----3' exonuclease is needed to excise the AP site: it falls off spontaneously. We have repaired DNA containing AP sites with an AP endonuclease (E. coli endonuclease IV or the chromatin AP endonuclease from rat liver), a DNA polymerase devoid of 5'----3' exonuclease activity (Klenow polymerase or rat liver DNA polymerase beta) and a DNA ligase. Catalysts of beta-elimination, such as spermine, can drastically shorten the already brief half-life of a 5'-terminal AP site; it is what very probably happens in the chromatin of eukaryotic cells. E. coli endonuclease IV also probably participates in the repair of strand breaks produced by ionizing radiations: as E. coli endonuclease VI/exonuclease III, it is a 3'-phosphoglycollatase and also a 3'-phosphatase. The 3'-phosphatase activity of E. coli endonuclease VI/exonuclease III and E. coli endonuclease IV can also be useful when the AP site has been excised by a beta delta-elimination reaction.     

Binding activities of thyroxine binding globulin versus thyroxine binding prealbumin in rat sera: differential modulation by thyroid hormone ligands, oleic acid and pharmacological drugs

We use gel equilibration and electrophoretic techniques to compare the binding properties of thyroxine binding globulin and thyroxine binding prealbumin in rat sera. The evidence indicates that TBG bears the serum lowest capacity highest affinity sites for thyroxine (T4) and triiodothyronine (T3) (Ka1 greater than or equal to 10(9) M-1) as well as weaker saturable T3 sites (Ka2 approximately 10(8) M-1). TBPA bears for T4 only Ka2 approximately 10(8) M-1 sites and for T3 only Ka approximately 10(6) M-1 sites. Consistent with these parameters are the specific responses of TBG and TBPA binding activities to varying serum concentrations of T4, T3, oleic acid, the drugs diphenylhydantoin or salicylate. The primary attack of these compounds is aimed at TBG. Small T4, oleate or DPH doses chase the TBG-bound T4 to TBPA, high doses of T4 or oleate but not of DPH inhibiting the T4 binding to both proteins. In the T3-serum interactions, all tested compounds displace the TBG-bound hormone without chasing it to TBPA. The high reactivity of TBG sites designates the protein as crucially involved in modulating the free vs bound serum levels of T4 and T3 against physiological or pathological variations of binding competitors.     

Studies on the submicrosomal fractions of bovine oligodendroglia: Lipid composition and glycolipid biosynthesis

Oligodendroglia were isolated from bovine brain, and a crude, microsomal fraction obtained from cell homogenates was subfractionated into myelin (MP), plasma membranes (PM), Golgi (GF), smooth (SER) and rough (RER) endoplasmic membranes using discontinuous-sucrose gradient centrifugation. The submicrosomal fractions were characterized by ultrastructural examination and analysis of the specific organelle markers. The myelin and plasma membrane rich fractions contained characteristically the highest amounts of the lipid with lower mole percentages of total phospholipids and phosphatidylcholine, and higher concentrations of phosphatidylethanolamine (+plasmalogens), cholesterol and galactolipids. Considerable amounts of the typical myelin galactolipids (galacto-cerebrosides, sulfatides and monogalactosyl diglycerides) were also found in the Golgi fraction (GF). The GF fraction had the greatest enrichment of glycolipid-forming galactosyltransferases, and the distribution of these enzymes correlated well with that of the Golgi marker enzymes. The results give evidence that intracellular Golgi apparatus of oligodendroglia is rich in the myelin-specific lipids, and suggest its involvement in the synthesis and processing of myelin lipids.