Biochemical effects of mild iron deficiency and cold acclimatization on rat skeletal muscle

Most of the previous studies on the effects of iron deficiency on skeletal muscle respiratory capacity and work performance have been investigated in severe or moderate iron-deficiency anemia. We report here that even in mild iron deficiency where the hemoglobin concentration was 10 g/dl and the iron stores in livers and spleen were not completely depleted, a marked reduction in succinate dehydrogenase was observed in skeletal muscles but not in heart. Similarly, cytochrome oxidase activities were reduced. Although no significant change in glycerophosphate dehydrogenase was detected in the iron-deficient rats, exposure to cold in this group greatly reduced this enzyme activity. As cold acclimatization accelerates marrow erythropoiesis (20) which in turn, demands more iron, it seems that in the iron-insufficient state, this iron demand for marrow activity may persist at the expense of the tissue iron pool, resulting in a marked reduction in glycerophosphate dehydrogenase activities. Since succinate dehydrogenase plays a significant role in the impairment of mitochondrial function and early fatigue of iron-deficient muscle (11), the present study shows that even in mild iron deficiency, some loss of muscle functions could result as succinate dehydrogenase activities were greatly reduced.     

Neural inhibition sharpens auditory spatial selectivity of bat inferior collicular neurons

This study examines the role of neural inhibition in auditory spatial selectivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, using a two-tone inhibition paradigm. Two-tone inhibition decreases auditory spatial response areas but increases the slopes of directional sensitivity curves of inferior collicular neurons. Inferior collicular neurons have either directionally-selective or hemifield directional sensitivity curves. A directionally-selective curve always has a peak which is at least 50% larger than the minimum. A hemifield directional sensitivity curve rises from an ipsilateral angle by more than 50% and either reaches a plateau or declines by less than 50% over a range of contralateral angles. Two-tone inhibition does not change directionally-selective curves but changes most hemifield directional sensitivity curves into directionally-selective curves. Auditory spatial selectivity determined both with and without two-tone inhibition increases with increasing best-excitatory frequency. Sharpening of auditory spatial selectivity by two-tone inhibition is larger for neurons with smaller differences between excitatory and inhibitory best frequencies. The effect of two-tone inhibition on auditory spatial selectivity increases with increasing inhibitory tone intensity but decreases with increasing intertone interval. The implications of these findings in bat echolocation are discussed. Accepted: 18 January 2000     

Evidence from nitrogen-15 and solvent deuterium isotope effects on the chemical mechanism of adenosine deaminase

We have determined 15N isotope effects and solvent deuterium isotope effects for adenosine deaminase using both adenosine and the slow alternate substrate 7,8-dihydro-8-oxoadenosine. With adenosine, 15N isotope effects were 1.0040 in H2O and 1.0023 in D2O, and the solvent deuterium isotope effect was 0.77. With 7,8-dihydro-8-oxoadenosine, 15N isotope effects were 1.015 in H2O and 1.0131 in D2O, and the solvent deuterium isotope effect was 0.45. The inverse solvent deuterium isotope effect shows that the fractionation factor of a proton, which is originally less than 0.6, increases to near unity during formation of the tetrahedral intermediate from which ammonia is released. Proton inventories for 1/V and 1/(V/K) vs percent D2O are linear, indicating that a single proton has its fractionation factor altered during the reaction. We conclude that a sulfhydryl group on the enzyme donates its proton to oxygen or nitrogen during this step. pH profiles with 7,8-dihydro-8-oxoadenosine suggest that the pK of this sulfhydryl group is 8.45. The inhibition of adenosine deaminase by cadmium also shows a pK of approximately 9 from the pKi profile. Quantitative analysis of the isotope effects suggests an intrinsic 15N isotope effect for the release of ammonia from the tetrahedral intermediate of approximately 1.03 for both substrates; however, the partition ratio of this intermediate for release of ammonia as opposed to back-reaction is 14 times greater for adenosine (1.4) than for 7,8-dihydro-8-oxoadenosine (0.1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Phospholipid-Sensitive Ca2+-Dependent Protein Kinase Preferentially Phosphorylates Serine-115 of Bovine Myelin Basic Protein

Phospholipid-sensitive Ca2+ -dependent protein kinase (PL-Ca-PK) and cyclic AMP-dependent protein kinase (A-PK) both preferentially phosphorylated serine residues of bovine myelin basic protein (MBP). Tryptic peptide maps of MBP phosphorylated by PL-Ca-PK or A-PK, however, revealed different phosphopeptides, suggesting a difference in the intramolecular substrate specificity for the two enzymes. Serine-115 of MBP, in the sequence (-Arg-Phe-Ser(115)-Trp-), was found to be a preferred and probably major phosphorylation site for PL-Ca-PK. Because serine-115 of bovine MBP corresponds to serine-113 of rabbit MBP, an in vivo phosphorylation site reported by Martenson et al. (1983), and PL-Ca-PK is present at a very high level in brain and myelin, it is suggested that the enzyme may be responsible for the in vivo phosphorylation of this and other sites in MBP.     

Solvent isotope effects on the reaction catalyzed by yeast hexokinase

The pH dependence of the maximum velocity (V) for the phosphorylation of glucose, the V/Kglucose and the V/KMgATP have been obtained in H2O and 2H2O. In H2O, V decreases below a pK of 5.8, V/Kglucose decreases below a pK of 6.1 and V/KMgATP decreases below a pK of 6.7. In 2H2O, complex behavior is observed for these parameters as a function of pD. The ratios of the parameters in H2O and 2H2O above their respective pK values give solvent deuterium isotope effects of about 1.5-1.7 for all three parameters. When 1,5-anhydromannitol is used as an alternative substrate, an isotope effect different than unity is obtained only for V/K1,5-anhydromannitol which gives a value of about 0.7. Both the complex pH profiles and the relative magnitude of the isotope effects are interpreted in terms of a pH-dependent change in the E X glucose complex.     

Effect of Ferricyanide, Ferrocyanide and KCN on Growth and Flowering in the Short-Day Plant Lemna paucicostata 6746

Flowering in the short-day plant Lemna paucicostata 6746 canbe induced under continuous light by the addition of ferricyanie,ferrocyanide or KCN to M-sucrose medium. Each substance is nearly10 times more effective when the flasks are covered by glassbeakers than when cotton plugs are used. By contrast, when floweringis induced under continuous light by copper or by short-daytreatment, neither flowering nor growth are affected by whetherglass beakers or cotton plugs are used. Ferricyanide, ferrocyanideand KCN are also able to induce long-day flowering when theplants are grown on Msucrose medium in small beakers that areplaced in a covered storage dish that also contains a solutionof one of these compounds. Addition of a KOH trap to the storagedish completely blocks the flowering induced by these compounds.If [¹⁴C]ferrocyanide is added to the storage dish both the M-sucrosemedium and the plants contain significant amounts of radioactivity,the amount of radioactivity being proportional to the floweringresponse. These results indicate that ferricyanide, ferrocyanideand KCN break down to release HCN and that it is the HCN whichis responsible for inducing flowering in L. paucicostata 6746under continuous light. ¹Present address: Department of Biology, Osaka Kyoiku University,Ikeda, Osaka 563, Japan. ²Present address: Institute of Horticulture, The Volcani Center,P. O. B. 6, Bet-Dagan, Israel. (Received January 17, 1983; Accepted March 24, 1983)     

Instability of the growth-limiting proteins of the Avena coleoptile and their pool size in relation to auxin

Summary The stability and pool size of the growth-limiting proteins (GLP) of the Avena coleoptile have been studied by measuring the time required for cycloheximide to inhibit the growth of auxin-treated segments. Inhibition of growth follows inhibition of protein synthesis by 20–25 min regardless of the growth rate. This indicates that the growth inhibition is due to inherent instability of the GLP rather than to exhaustion of the pool through growth. A study of the amount and rate of auxin-induced growth which occurs when cycloheximide is added just before or after the auxin indicates that the rate of elongation is determined by the size of the GLP pool, and that the pool of GLP is low in the absence of auxin, but rapidly expands and reaches a maximum 20–25 min after addition of auxin. Three ways in which auxin might expand the pool of GLP are discussed.     

Vorkommen und Eigenschaften der proteolytischen Enzyme des Magensaftes und der Mitteldarmdrüse des Flußkrebses Astacus astacus (L.) und Cambarus affinis (Say)

Zusammenfassung Es werden die Exopeptidase- und Dipeptidaseaktivitäten des Hepatopankreas und Magensaftes von Astacus astacus (L.) und Cambarus affinis (Say) quantitativ bestimmt (Durchschnittswerte von ca. 90 Tieren). Die besonders im Magensaft vorkommende Carboxypeptidase hydrolysiert Carbobenzoxyglycyl-l- phenylalanin und Carbobenzoxy-l-glutamyl-l-tyrosin ungefähr gleichstark (pH-Optimum 7,6 bzw. 7,0). Im Vergleich zur kristallisierten Pankreascarboxypeptidase wird das Magensaftenzym stärker durch Hydrozimtsäure als durch o-Phenanthrolin gehemmt. SH-Gruppen sind für die Wirkung nicht nötig. Die Leucinamid- und Leucin--naphthylamid-Hydrolyse ist nicht auf die klassische Leucinaminopeptidase, sondern auf eine metallionenunabhängige und puromycinempfindliche Arylamidase-ähnliche Wirkung (pH-Optimum 7,7–8,0) zurückzuführen. Amidase- und Dipeptidase (Substrat: Glycyl-l-lencin)-Wirkung sind besonders im Hepatopankreas aktiv.

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Occurrence and properties of proteolytic enzymes in the gastric juice and hepatopancreas of the crayfishes Astacus astacus (L.) and cambarus affinis (Say)I. Exopeptidases

Summary The exopeptidase and dipeptidase activities of the hepatopanereas and gastric juice of Astacus astacus (L.) and Cambarus affinis (Say) were determined (mean values from approximately 90 exemplares). The carboxypeptidase which was highly active in the gastric juice hydrolyzes carbobenzoxyglycyl-l-phenylalanine and carbobenzoxy-l-glutamyl-l-tyrosine at about the same rate (pH-optimum at 7,6 and 7,0 respectively). Compared with the crystalline pancreas carboxypeptidase the gastric juice enzyme was stronger inhibited by hydrocinnamic acid than by o-phenanthroline. Sulfhydryl groups are not essential for the enzyme action. The observed hydrolysis of leucine amide and leucine--naphthyl amide could not be attributed to the classic leucine aminopeptidase but to an arylamidase like action (pH Optimum 7,7 to 8,0) which was independent of metal ions and puromycin-sensitive. The amidase and dipeptidase (substrate: glycyl-l-leucine) are mainly localized in hepatopanereas.