Changes in the Activity of the Maturation-Promoting Factor Are Correlated with Those of a Major Cyclic AMP and Calcium-Independent Protein Kinase During the First Mitotic Cell Cycles in the Early Starfish Embryo

Many studies suggest that MPF activation depends on protein phosphorylation or that MPF is itself a protein kinase. In the present report, cyclic variations of MPF activity have been correlated in vivo with changes in the extent of protein phosphorylation or in vitro with changes of a major protein kinase during the first cell cycles of fertilized starfish eggs. This cycling protein kinase neither requires cAMP nor Ca²⁺. Neither colchicine nor aphidicoline, which inhibits cleavage and chromosome replication respectively, was found to suppress the synchronous and cyclic variations of both MPF and protein kinase activities. Protein synthesis was found to be required for both MPF and protein kinase activities to reappear after their simultaneous drop at the time of mitotic or meiotic cleavages. Production of either MPF or protein kinase activities is not the immediate result of protein synthesis since there is a delay at each cell cycle between the time when protein synthesis is required and the time when both MPF and protein kinase activities are produced. This suggests that both MPF and protein kinase activities might involve some post-translational modification of a precursor protein synthesized during the preceeding cell cycle.     

Changes in the acinar distribution of some enzymes involved in carbohydrate metabolism in rat liver parenchyma after experimentally induced cholestasis

Extrahepatic cholestasis induced by ligation and transsection of the common bile duct caused a change in the parenchyma/stroma relationship in rat liver. Two weeks after ligation, the periportal zones of the parenchyma were progressively invaded by expanding bile ductules with surrounding connective tissue diverging from the portal areas. Parenchymal disarray developed and small clumps of hepatocytes or isolated hepatocytes were scattered within the expanded portal areas. These cells showed normal activity of lactate, succinate and glutamate dehydrogenase and may, therefore, be considered to be functionally active. After cholestasis the remainder of the liver parenchyma showed adaptational changes with respect to glucose homeostasis, as demonstrated by histochemical means. Glycogen stores disappeared completely whereas glycogen phosphorylase activity increased about ten fold. The increased glycogen phosphorylase activity and glycogen depletion indicate a greater glycogenolytic capacity in liver parenchyma after bile duct ligation to maintain as far as possible a normal plasma glucose concentration. The parenchymal distribution pattern of glucose-6-phosphatase activity did not change significantly after bile duct ligation. The isolated hepatocytes within the expanded portal tracts showed a high activity of this enzyme whereas the pericentral parenchyma was only moderately active. The distribution patterns of glucose-6-phosphate dehydrogenase and lactate dehydrogenase activity in the liver parenchyma were also largely unchanged after bile duct ligation, but the histochemical reaction for glucose-6-phosphate dehydrogenase activity demonstrated infiltration of the remainder of the parenchyma by non-parenchymal cells, possibly Küpffer cells and leucocytes as part of an inflammatory reaction. Under normal conditions the mitochondrial enzymes succinate and glutamate dehydrogenase show an opposite heterogenous distribution pattern in liver parenchyma. Following cholestasis both enzymes became uniformly distributed. The underlying regulatory mechanism for these different changes in distribution patterns of enzyme activities is not yet understood.     

In situ kinetic parameters of glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase in different areas of the rat liver acinus

The reaction velocity of glucose-6-phosphate dehydrogenase (G6PDH) and phosphogluconate dehydrogenase (PGDH) was quantified with a cytophotometer by continuous monitoring of the reaction product as it was formed in liver cryostat sections from normal, young mature female rats at 37 degrees C. Control incubations were performed in media lacking both substrate and coenzyme for G6PDH activity and lacking substrate for PGDH activity. All reaction rates were non-linear but test minus control reactions showed linearity with incubation time up to 5 min using Nitro BT as final electron acceptor. End point measurements after incubation for 5 min at 37 degrees C revealed that the highest specific activity of G6PDH was present in the intermediate area (Vmax = 7.79 +/- 1.76 mumol H2 cm-3 min-1) and of PGDH in the pericentral and intermediate areas (Vmax = 17.19 +/- 1.73 mumol H2 cm-3 min-1). In periportal and pericentral areas, Vmax values for G6PDH activity were 4.48 +/- 1.03 mumol H2 cm-3 min-1) and 3.47 +/- 0.78 mumol H2 cm-3 min-1), respectively. PGDH activity in periportal areas showed a Vmax of 10.84 +/- 0.33 mumol H2 cm3 min-1. Variation of the substrate concentration for G6PDH activity yielded similar KM values of 0.17 +/- 0.07 mM, 0.15 +/- 0.13 mM and 0.22 +/- 0.11 mM in periportal, pericentral and intermediate areas, respectively. KM values of 0.87 +/- 0.12 mM in periportal and of 1.36 +/- 0.10 mM in pericentral and intermediate areas were found for PGDH activity. The significant difference between KM values for PGDH in areas within the acinus support the hypothesis that PGDH is present in the cytoplasmic matrix and in the microsomes. A discrepancy existed between KM and Vmax values determined in cytochemical assays using cryostat sections and values calculated from biochemical assays using diluted homogenates. In cytochemical assays, the natural microenvironment for enzymes is kept for the demonstration of their activity and thus may give more accurate information on enzyme reactions as they take place in vivo.     

Molecular extinction coefficients of lead sulfide and polymerized diaminobenzidine as final reaction products of histochemical phosphatase reactions.

Molar extinction coefficients of precipitated lead sulfide (PbS) and polymerized diaminobenzidine (polyDAB) have been determined at wavelengths of 450 nm and 480 nm, respectively, for quantitative histochemical analysis of phosphatase reactions. These values are essential for the conversion of cytophotometric (mean integrated) absorbance values to absolute units of substrate converted per unit time and volume of tissue. This conversion allows direct comparison of histochemical and biochemical data. The molar extinction coefficient of PbS at 450 nm was found to be 3,800 and therefore, per mole phosphate liberated, the molar extinction coefficient is 5,700 because 3 moles phosphate are captured by 2 moles lead at neutral or alkaline pH. Parallel experiments with the cerium-DAB method revealed that the molar extinction coefficient of polyDAB at 480 nm is 5,500 with respect to liberated phosphate. The molar extinction coefficients were applied for comparison of data from biochemical and histochemical assays of glucose-6-phosphatase activity in rat livers. A significant correlation was found between both sets of data. The values were in the same order of magnitude with histochemical values approximately 1.4 times higher than biochemical values.     

中国平脉树螽属五新种记述：直翅目：螽斯科：树螽亚科

本文报道中国平脉树螽属5个新种。每个新种皆有详细的形态描述和形态特征图。所有模式标本存于北京农业大学昆虫标本室。     

Changes in Abscisic Acid Content in Axis and Cotyledons of Developing Phaseolus vulgaris Embryos and their Physiological Consequences

Prevost, I. and Le Page–Degivry, M. Th. 1985. Changesin absicisic acid content in axis and cotyledons of developingPhaseolus vulgaris embryos and their physiological consequences.—J.exp. Bot. 36: 1900–1905.Changes in abscisic acid (ABA)content with time were measured in embryonic axes and in cotyledonsof Phaseolus vulgaris embryos using a radio–immunoassay.During embryogenesis, a similar pattern was observed in bothtissues: ABA increased to a maximum 29 d after an thesis, followedby a decrease as the seed matured. The level of ABA in the cotyledonswas always much higher than that in the axes. In in vitro cultures,the duration of the lag phase before germination of isolatedembryonic axes increased with ABA content. The presence of cotyledonsalways lengthened the lag phase; longer lag phases were associatedwith greater concentrations of ABA in the cotyledons. Moreoverthe presence of cotyledons stimulated the growth of seedlings. Key words: ABA distribution, embryo maturation, axis and embryo germinability     

Quantitative histochemical analysis of glucose-6-phosphatase activity in rat liver using an optimized cerium-diaminobenzidine method

We have optimized a cerium-diaminobenzidine-based method for histochemical analysis of glucose-6-phosphatase (G6Pase) activity and have determined quantitative data on the zonal distribution pattern in the liver acinus of fasted male rats. In the cerium-diaminobenzidine technique, cerium instead of lead ions is used as capturing reagent for the enzymatically liberated phosphate. For light microscopy, the primary reaction product, cerium phosphate, is then visualized by conversion into cerium perhydroxide using hydrogen peroxide and subsequent oxidative polymerization of diaminobenzidine to diaminobenzidine brown as the final reaction product. Variation of the substrate (glucose-6-phosphate) concentration in the incubation medium yielded in periportal zones a KM value of 2.3 +/- 0.7 mM and a Vmax value of 0.96 +/- 0.18 (expressed as mean integrated absorbance). In perivenous zones a KM value of 1.1 +/- 0.4 mM and a Vmax value of 0.51 +/- 0.08 were calculated. The cytophotometric analysis performed in this study demonstrated for the first time that a functional difference of G6Pase, the key enzyme for gluconeogenesis, exists in the periportal and perivenous zones of the liver acinus. Periportal zones contain twice as many enzyme molecules (high Vmax) as perivenous zones, but the affinity for the substrate is twice as low. This may have important implications for the concept of metabolic zonation of the liver and also for glucose homeostasis in the blood.