Studies on (pro)insulin biosynthesis and secretion of pancreatic islets of sand rats (Psammomys obesus) after different feeding conditions.

It was possible to induce different metabolic states in sand rats of our breeding colony or in newly caught Egyptian sand rats, respectively, by feeding a pellet diet or vegetable diet (green cabbage). Newly captured sand rats fed only on native food were used as reference group (group C). Plasma IRI-level and glucose in vivo and [3H]-leucine incorporation into proinsulin and insulin, insulin secretion and insulin content in vitro were investigated. Sand rats fed on pellet chow and ad libitum (group B) developed a hyperinsulinism and showed higher sensitivity of [3H]-leucine incorporation into proinsulin and insulin to glucose (maximal stimulation at 3 mM) and increased incorporation rates in vitro. Restriction of pellet food to 35-40 kcal/animal/day (group A) lead to changes of all parameters, which were investigated in the same direction as in group B, but to a much smaller extent. Newly captured sand rats, which were fed green cabbage for 4 to 6 weeks divided into two groups: One group (group D1) was comparable to the normal group (C) in IRI levels, glucose levels, glucose sensitivity and amount of [3H]-leucine incorporation. The other group (group D2) tended to group A. Marked changes in insulin content and insulin secretion of isolated pancreatic islets could not be found in any group.     

Investigation of the structure of two-phase flow fermentation model media in bubble-column bioreactors

Summary Electrical conductivity microprobes have been used to estimate the transverse variation of bubble size, local gas holdup and local specific gas/liquid interfacial area in bench scale bubble column bioreactors containing fermentation model media. Inserted O₂-electrodes and plane parallel windows alter the structure of the two phase flow. Even slight tilting of the column strongly influences the transverse profiles of the bubble size and local gas holdup. The larger bubbles are collected at the wall, where they can be redispersed. These observations open up new possibilities for the construction of bubble column bioreactors.     

Comparison of the bile salts of frogs with those of their tadpoles. Bile-salt changes during the metamorphosis of Rana Catesbeiana Shaw.

1. The bile salts of three frog species of the genus Ptychadena and of Rana catesbeiana have been compared with those of their tadpoles. For R. catesbeiana comparison was made of the bile salts in at least ten of the recognized stages of tadpole metamorphosis. 2. In all cases, adult bile salts were more complex than those of the tadpoles. 3. In R. catesbeiana after stage 18, 26-deoxy-5 alpha-ranol was hydroxylated to form 5 alpha-ranol (27-nor-5 alpha-cholestane-3 alpha, 7 alpha, 12 alpha, 24 xi, 26-pentol) and at least two other bile alcohols appeared in solvolysed bile salts. 4. Tadpole bile salts were not found to be biochemically more primitive than those of fully metamorphosed frogs; in some, but not all, cases tadpole bile alcohols could be regarded as biochemical precursors of those in the adult frogs. 5. Detailed evidence for the structure of the bile salts from mass-spectral fragmentation patterns has been deposited as Supplementary Publication SUP 50097 (2 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169, 5.     

Nickel,cobalt, and molybdenum requirement for growth of Methanobacterium thermoautotrophicum

Growth of Methanobacterium thermoautotrophicum on H₂ and CO₂ as sole energy and carbon sources was found to be dependent on Ni, Co, and Mo. At low concentrations of Ni (<100 nM), Co (<10 nM) and Mo (<10 nM) the amount of cells formed was roughly proportional to the amount of transition metal added to the medium; for the formation of 1 g cells (dry weight) approximately 150 nmol NiCl₂, 20 nmol CoCl₂ and 20 nmol Na₂MoO₄ were required. A dependence of growth on Cu, Mn, Zn, Ca, Al, and B could not be demonstrated. Conditions are described under which the bacterium grew exponentially with a doubling time of 1.8 h up to a cell density of 2 g cells (dry weight)/1.     

Kinetic characteristics of the sulfate self-exchange in human red blood cells and red blood cell ghosts

Summary The sulfate and the chloride self-exchange fluxes were determined by measuring the rate of the tracer efflux from radioactively labeled human red blood cells and red blood cell ghosts. The concentration dependence and the pH-dependence of the sulfate self-exchange flux were studied. In addition, the effects of some monovalent and divalent anions on the sulfate and the chloride self-exchange fluxes were investigated.The sulfate self-exchange fluxes saturate, exhibiting a concentration maximum at sulfate concentrations between 100 and 300mm (25°C). The position of the concentration maximum depends upon pH. At high sulfate concentrations a self-inhibition of the flux becomes apparent. The apparent half-saturation constant and the apparent self-inhibition constant at pH 7.2 were 30mm and 400mm respectively. Within the pH range of 6.3–8.5, both constants decreased with increasing pH. No saturation of the sulfate self-exchange flux was observed if the sulfate concentration was raised by substituting sulfate for isoosmotic amounts of a second salt (NaCl, NaNO₃, Na-acetate, Na-lactate, Na-succinate or Na₂HPO₄). Red blood cells and red blood cell ghosts display the same pattern of concentration responsiveness.The sulfate self-exchange flux exhibits a pH-maximum at about pH 6.2 (37°C). The location of the pH-maximum is little affected by variations of the sulfate concentration. The logarithmic plots (log vs. pH) revealed that the flux/pH relation can be approximated by two straight lines. The slopes of the alkaline branches of the flux/pH curves range from –0.55 to –0.86, the slopes of the branches of the curves range from 0.08 to 1.14 and were strongly affected by changes of the sulfate concentrations. The apparent pK's obtained from the alkaline and from the acidic branches of the flux/pH curves were about 7.0 and 6.0, respectively. Intact red blood cells and red blood cell ghosts display the same type of pH-dependency of the sulfate self-exchange flux.The sulfate self-exchange flux is competitively inhibited by nitrate, chloride, acetate, oxalate and phosphate. The chloride self-exchange flux is competitively inhibited by thiocyanate, nitrate, sulfate and phosphate. The inhibition constants for the various anion species increase in the given sequence.The results of our studies indicate that the sulfate self-exchange flux is mediated by a two-site transport mechanism consisting either of a mobile carrier or a two-site pore. The experiments reported in this paper do not permit distinguishing between both transport mechanisms. The similarities of the sulfate and the chloride self-exchange flux and the mutual competition between sulfate and chloride point to a common transport system for both anion species.     

Pyruvate fermentation in Rhodospirillum rubrum and after transfer from aerobic to anaerobic conditions in the dark

The fermentative metabolism of Rhodospirillum rubrum (strain Ha, F₁, S₁) was studied after transfering the cells from aerobic to anaerobic dark culture conditions. Pyruvate was metabolized mainly to acetate and formate, and to a lesser extent to CO₂ and propionate, by all strains. Therefore, pyruvate formate lyase would appear to be the characteristic key enzyme of the dark anaerobic fermentation metabolism in R. rubrum. Strain F₁ and S₁ metabolized the formate further to H₂ and CO₂. It is concluded that this cleavage was catalysed by a formate hydrogen lyase system. Strain Ha was unable to metabolize formate. The cleavage of formate and the synthesis of poly--hydroxy-butyric acid were increased by a low pH value (6.5). Fermentation equations and schemes of the pyruvate metabolism are discussed.