Fine structure and metabolism of multiply innervated fast muscle fibres in teleost fish

Summary Both the fast and slow muscle fibres of advanced teleost fish are multiply innervated. The fraction of slow-fibre volume occupied by mitochondria is 31.3%, 25.5% and 24.6%, respectively, for the myotomal muscles of brook trout (Salvelinus fontinalis), crucian carp (Carassius carassius), and plaice (Pleuronectes platessa), respectively. The corresponding figures for the fast muscles of these species are 9.3%, 4.6% and 2.0%, respectively. Cytochrome-oxidase and citrate-synthetase activities in the fast muscles of 9 species of teleost range from 0.20–0.93 moles substrate utilised, g wet weight muscle^-1 min^-1 (at 15° C) or around 4–17% of that of the corresponding slow fibres. Ultrastructural analyses reveal a marked heterogeneity within the fast-fibre population. For example, the fraction of fibres with <1% or >10% mitochondria is 0,4,42% and 36, 12 and 0%, respectively, for trout, carp and plaice. In general, small fibres (<500 m²) have the highest and large fibres (>1,500 m²) the lowest mitochondrial densities. The complexity of mitochondrial cristae is reduced in fast compared to slow fibres.Hexokinase activities range from 0.4–2.5 in slow and from 0.08–0.7 moles, g wet weight^-1 min^-1 in fast muscles, indicating a wide variation in their capacity for aerobic glucose utilisation. Phosphofructokinase activities are 1.2 to 3.6 times higher in fast than slow muscles indicating a greater glycolytic potential. Lactate dehydrogenase activities are not correlated with either the predicted anaerobic scopes for activity or the anoxic tolerances of the species studied. The results indicate a considerable variation in the aerobic capacities and principal fuels supporting activity among the fast muscles of different species. Brook trout and crucian carp are known to recruit fast fibres at low swimming speeds. For these species the aerobic potential of the fast muscle is probably sufficient to meet the energy requirements of slow swimming.     

Kinetic properties of a L-cysteine desulfhydrase-deficient mutant in the enzymatic formation of L-cysteine from D,L-ATC

Summary A mutant strain lacking in activity of L-cysteine desulfhydrase, a L-cysteine-decomposing enzyme, was screened after UV-treatment ofPseudomonas sp. CU6. The properties of the two strains, original and mutant, were compared on the basis of parameter values estimated from kinetic simulations of the enzymatic formation of L-cysteine from D,L-ATC. Both strains suffered from product inhibition, though inhibition was less for the mutant strain.     

Somatic embryogenesis from leaf callus of mature plants of the gymnospermCeratozamia mexicana var. robusta (Miq.) dyer (Cycadales)

Summary Embryogenic callus was induced from explanted pinnae of newly emerged leaves of mature plants ofCeratozamia mexicana var. Robusta (Gymnospermae, Cycadales) on a modified B5 formulation with 1 mg·liter⁻¹ kinetin and 1 mg·liter⁻¹ 2,4-dichlorophenoxyacetic acid. Proembryos developed on induction medium, but they were more numerous after subculture onto phytohormone-free medium, which also enabled suspensors to elongate. For nearly 1.5 yr after explanting, subsequent development of somatic embryos was not observed as suspensors dedifferentiated to form embryogenic callus on phytohormone-free medium. After this time, cotyledonary somatic embryos developed at the distal end of the suspensors. Somatic embryos have germinated on phytohormone-free medium. This is the first report of regeneration by somatic embryogenesis of a gymnosperm species from a mature tree. This technique has great potential for preservation of the highly endangered cycads.     

Work flow control in the flexible flow line

This research involves the development and evaluation of a part flow control model for a type of flexible manufacturing system (FMS) called a dedicated flexible flow line (FFL). In the FFL, all part types flow along the same path between successive machine groups. The specific objective of the part flow control model for the FFL is to minimize makespan for a given set of parts produced in a FFL near-term schedule, given fixed available buffer constraints. The control model developed in this research involved the repeated, real-time execution of a mathematical programming algorithm. The algorithm attempts to release the right mix of parts at the tight time to keep the FFL operating smoothly. The focus of the approach is directed toward managing WIP buffers for each machine group queue. The algorithm specifically incorporates stochastic disturbance factors such as machine failures. Through a limited number of simulation experiments, performance of the control model is shown to be superior to other parts releasing and control methods reported in the literature.     

Nuclear interactions of retinoic acid-binding protein in chemically induced mammary adenocarcinoma.

Cellular retinoic acid-binding protein (CRABP) was detected in the nuclear fraction of N-methyl-N-nitrosourea-induced mammary cancers after the incubation of cytosol containing [3H]retinoic acid (RA)-bound CRABP with isolated nuclei. CRABP extracted from the nuclei in buffer containing 0.4 M-KCl sedimented as a 2 S component when subjected to sucrose-density-gradient analysis. [3H]RA-CRABP was found to be a prerequisite for the detection of nuclear binding, since the incubation of isolated nuclei or 0.4 M-KCl extract of the nuclei with [3H]RA did not result in any significant binding. Incubation of [3H]RA-CRABP at 25 or 30 degrees C before incubation with the nuclei neither altered the sedimentation coefficient nor enhanced the nuclear binding compared with 0 degrees C incubation. The tumour nuclei contained a saturable number of binding sites with a dissociation constant of 1.6 x 10(-9) M. These results indicate that the action of retinoic acid in the target organ may be mediated by its interaction with the nuclei.     

Amino acid transport and interconversions in tissues of freshly caught and food-deprived plaice, Pleuronectes platessa L.

Distribution ratios (intracellular/extracellular concentration) of α-amino isobutyric acid (AIB) and activities of the transaminases of alanine (Ala AT), aspartate (Asp AT), leucine (Leu AT) and glutamate dehydrogenase (GDH) were determined in tissues of freshly caught plaice, Pleuronectes platessa , deprived of food for three months. Liver, red muscle and white muscle demonstrated increased distribution ratios for AIB, while the ratios decreased in kidney and gill with deprivation. Values of the distribution ratio were below 1.0 only in white muscle, with kidney and liver having the highest absolute values. Transaminase activities generally rose with deprivation in all tissues, although the absolute increases were greatest in liver and for the two enzymes Ala AT and GDH. These data indicate that with food deprivation, the role of the liver in amino acid metabolism is maintained and slightly enhanced, while that of the kidney is reduced. Both muscle types (red and white) showed increased water content implicating protein mobilization which could enhance the availability of amino acids for liver gluconeogenesis and metabolite sparing in other tissues during conditions of depletion.     

Progression of Epiphytic Microflora in Wheat and Alfalfa Silages as Observed by Scanning Electron Microscopy

Wheat and alfalfa silages were examined by scanning electron microscopy and standard methods of microbial enumeration. Epiphytic microflora were present at levels of 10⁶ to 10⁸/g in the fresh-cut plants. This flora was initially observed microscopically primarily on the surfaces. After 4 days of fermentation, lactic acid bacteria were observed on the surface in high concentrations near open stomata and throughout the interior mesophyll air sac spaces. At 4 days, populations on interior surfaces were restricted to the exterior surfaces of the air sacs. After 8 days the mesophyllic cells showed marked deterioration, and bacteria were observed on their inner surfaces. At 32 days, the end of the fermentation, vascular bundles and epidermal cells remained intact whereas stomata and mesophyllic cells were collapsed and often contained microorganisms. It is concluded that the interior of the leaves offers substantial nutritional and environmental advantages to epiphytic flora and is an important if not major deterioration site in fermented products. Since little deterioration of exterior surfaces was observed, these sites may play a minor role in supplying nutrients for microbial growth.     

Analysis of structural polypeptides of purified human cytomegalovirus.

Human cytomegalovirus strain C87 was purified by the following procedures. (i) Extracellular virus was concentrated by centrifugation at 100,000 X g for 90 min and passed through a Bio-Rad Bio-Gel A-15m column. Most of the virus was recovered in the void volume. (ii) After two consecutive isopycnic potassium tartrate gradient centrifugations (20 to 50%), coinciding peaks of plaque titer, protein, and radioactivity were found at a density of from 1.20 to 1.21 g/cm3. To characterize the structural polypeptides of human cytomegalovirus and to establish relative purification criteria, virus was purified from two mixtures: (i) [35S]methionine-labeled extracellular virus mixed with an equal volume of unlabeled normal culture fluid; (ii) unlabeled extracellular virus mixed with an equal volume of [357a1methionine-labeled normal culture fluid. The extent of purification, as judged by the ratio of cellular to viral radioactivity, was 39-fold; i.e. about 2.5% of the protein in the purified virus preparation could be accounted for by host protein contamination. Electrophoresis of purified [35S]methionine-labeled virus on a polyacrylamide gel slab showed that there were at least 33 viral structural polypeptides (VPs), and their molecular weights ranged from 11,000 to 290,000. Autoradiograms obtained from electropherograms of purified [14C]glucosamine labeled virus showed six bands. Four of these were so broad that several VPs corresponded to each of the glycosylated bands. When heavy (two fractions close to 1.21 g/cm3) and light (two fractions close to 1.20 g/cm3) fractions of the PFU peak from the second potassium tartrate gradient were analyzed separately, the number of polypeptides observed was the same, but the relative amounts of some polypeptides differed. The major polypeptide, VP17, was found in greater amounts in the heavy fraction (35%) than in the light fraction (22%). The amount of DNA as a percentage of the weight of protein was 2% for the light fraction and 1% for the heavy fraction.