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Biomedical subjects

R Menzel

Publications and source records attributed to R Menzel.

At least 127 records · Page 7Linked to original sources
PubMed1984

Methods and effects of improved conventional insulin treatment in labile insulin-dependent diabetes (IDDM).

In 92 particularly unstable IDDM patients we have tried to avoid any gap in daily insulin supply by applying one out of four newly designed combinations of regular and depot insulin. The short-term effect after three weeks and the long-term effect after greater than or equal to 12 months (data from 30 patients only) of these new regimens were compared with those of the traditional regimen in a retrospective evaluation: Glycemia (level and excursions) was significantly improved both after three weeks of inpatient treatment and after greater than or equal to 12 additional months on outpatient regimen. Serum beta-LP and HbA1 showed slight decrease during long-term follow-up. The majority of the patients reported improved well-being under conditions of daily life. However, the glycemia achieved was still far from the permanent euglycemia aimed at. For the avoidance of any gap in insulin supply in labile diabetics four insulin injections are necessary in most cases. For this, individually tailored combinations of regular and depot insulin must be drawn up carefully together with the patients to avoid a " strait -jacket" system which would not work under conditions of daily life.

Adult↗
PubMed1983

Regulation of the genes for E. coli DNA gyrase: homeostatic control of DNA supercoiling.

DNA gyrase is the bacterial enzyme responsible for converting circular DNA to a negatively supercoiled form. We show that the synthesis of DNA gyrase is itself controlled by DNA supercoiling; synthesis is highest when the DNA template is relaxed. The rates of synthesis in vivo of both the A and B subunits of DNA gyrase are increased up to 10-fold by treatments that block DNA gyrase activity and decrease the supercoiling of intracellular DNA. Similarly, efficient synthesis of both gyrase subunits in a cell-free S-30 extract depends on keeping the closed circular DNA template in a relaxed conformation. The results suggest that DNA supercoiling in E. coli is controlled by a homeostatic mechanism. Synthesis of the RecA protein and several other proteins is also increased by treatments that relax intracellular DNA.

Bacterial Proteins↗
PubMed1983

Portable insulin infusion devices: a new era in the treatment of insulin-dependent diabetics! Which patients should be treated?

The development of portable insulin infusion devices - in which the insulin dosage is programmed in advance (open loop system) are increasingly being used for long-term daily diabetes control. These pumps represent a new method for attaining significantly improved metabolic control (glycemia and glucose metabolites, HbA1, lipid and aminoacid metabolism) and an impressive influence on diabetic neuropathy, on general fitness and on quality of life of insulin-dependent diabetics. At least all insulin-dependent diabetics without noticeable residual insulin secretion should be treated by continuous subcutaneous insulin infusion (CSII) via portable pumps, that are 8 000-10 000 patients in the GDR and approximately 500 000 in the world. Considering special conditions (strict supervision by experienced medical staff, carefully drawn up adequate instructions, highly motivated and capable patients) we assume that at the present stage of technical development of the pumps infants, imbeciles and incooperatives should be excepted only.

Adolescent↗
PubMed1983

Classical conditioning of proboscis extension in honeybees (Apis mellifera).

Extension of the proboscis was conditioned in restrained honeybees with odor as the conditioned stimulus (CS) and sucrose solution--delivered to the antenna (to elicit extension of the proboscis) and then to the proboscis itself--as the unconditioned stimulus (US). In a first series of experiments, acquisition was found to be very rapid, both in massed and in spaced trials; its associative basis was established by differential conditioning and by an explicitly unpaired control procedure (which produced marked resistance to acquisition in subsequent paired training); and both extinction and spontaneous recovery in massed trials were demonstrated. In a series of experiments on the nature of the US, eliminating the proboscis component was found to lower the asymptotic level of performance, whereas eliminating the antennal component was without effect; reducing the concentration of sucrose from 20% to 7% slowed acquisition but did not lower the asymptotic level of performance; and second-order conditioning was demonstrated. In a series of experiments on the role of the US, an omission contingency designed to eliminate adventitious response-reinforcer contiguity was found to have no adverse effect on acquisition. In a series of experiments designed to analyze the resistance to acquisition found after explicitly unpaired training in the first experiments, no significant effect was found of prior exposure either to the CS alone or to the US alone, although the unpaired procedure again produced substantial resistance that was shown to be due to inhibition rather than to inattention; extinction after paired training was found to be facilitated by unpaired presentations of the US. The relation between these results for honeybees and those of analogous experiments with vertebrates is considered.

Animals↗
PubMed1981

Purification of the putA gene product. A bifunctional membrane-bound protein from Salmonella typhimurium responsible for the two-step oxidation of proline to glutamate.

In this paper we report the purification of a protein which is able to catalyze both the proline oxidase and the pyrroline-5-carboxylic acid dehydrogenase activities necessary for the oxidation of proline to glutamic acid. The purification involves the preparation of a crude membrane pellet, detergent solubilization, ammonium sulfate fractionation, and DEAE-chromatography. We are able to obtain an essentially pure preparation (greater than 95% pure) after only a 52-fold purification, demonstrating that the protein is a major protein in cells fully induced for proline utilization. Both proline oxidase and pyrroline-5-carboxylic acid dehydrogenase activities co-purity throughout our purification. Velocity sedimentation of the purified protein demonstrates that both proline oxidase and pyrroline-5-carboxylic acid dehydrogenase activities co-sediment. Early in the purification procedure we are able to detect two species of protein which have both proline oxidase and pyrroline-5-carboxylic acid dehydrogenase activities. Our procedure purifies only the larger molecular weight species. The purified protein is a dimer composed of identical 132,000-dalton subunits. Analysis of mutants defective for proline utilization demonstrate that the bifunctional enzyme is the putA gene product.

1-Pyrroline-5-Carboxylate Dehydrogenase↗
PubMed1981

Enzymatic properties of the purified putA protein from Salmonella typhimurium.

In the previous paper (Menzel, R., and Roth, J. (1981) J. Biol. Chem. 256, 9755-9761) we have described the purification of a protein, the putA gene product, which has both proline oxidase and pyrroline-5-carboxylic acid dehydrogenase activities. In this paper we demonstrate that these enzyme activities are distinct with respect to a number of characteristics. The oxidase activity proceeds by a ping-pong mechanism involving the reduction of an enzyme-bound flavin. The dehydrogenase activity utilizes an ordered reaction mechanism.

1-Pyrroline-5-Carboxylate Dehydrogenase↗
PubMed1980

Identification and mapping of a second proline permease Salmonella typhimurium.

In this paper we demonstrate the existence of a second proline permease, gene proP, in Salmonella typhimurium. Uptake assays demonstrate that this second proline permease has 5 to 10% the uptake rate of the putP permease, the cell's major proline permease, when assayed at 20 microM proline. Genetic mapping by Hfr and P22-mediated genetic crosses placed the second proline permease gene at 92 min on the S. typhimurium genetic map, near the genes for melibiose utilization. F'-mediated complementation tests indicated that Escherichia coli also has the proP gene.

Chromosome Mapping↗
PubMed1980

Biochemistry and regulation of a second L-proline transport system in Salmonella typhimurium.

This paper reports some biochemical characteristics of a second L-proline transport system in Salmonella typhimurium. In the accompanying paper, R. Menzel and J. Roth (J. Bacteriol. 141:1064--1070, 1980) have identified this system by showing that it is inactivated by mutations at the locus proP. We have found that it is an active transport system with an apparent Km for L-proline of 3 x 10(-4) M and a strict specificity for L-proline and some of its analogs. Unlike the L-proline transport system encoded in putP, this second system is induced by amino acid limitation.

Amino Acids↗
PubMed1979

Behavioural access to short-term memory in bees.

Memory formation proceeds in temporal phases which differ in their effectiveness in controlling subsequent behavior and in their susceptibility to amnestic treatment. The initial phase of memory formation, frequently termed short-term memory, is generally considered a necessary precursor to long-term memory. However, the course of short-term memory differs widely between animal species and is dependent on experimental procedure. Information may even bypass the short-term phase en route to the long-term one. Experiments reported here using honey bees in a behavioural learning situation suggest that the greatest significance of short-term memory is its function as a mode of memory storage which may be altered effectively by new and contradictory information. Freely flying honey bees were presented two colour alternatives and rewarded on first one and then the other in a reversal learning paradigm. Subsequent colour preference was dependent on the interval between the two trials. Several new features of short-term memory are described. It is concluded that a single mechanisms of short- to long-term memory transfer cannot account for the observed bimodal interval dependent behaviour. Two mechanisms are proposed.

Animals↗