Localization of chicken muscle FBPase in cardiomyocyte nuclei

Kinetic properties of Pelophylax esculentus muscle FBPase

D-Fructose-1,6-bisphosphate 1-phosphohydrolase FBPase; [EC 3.1.3.11] was isolated from Pelophylax esculentus muscle in an electrophoretically homogeneous form with ca 30% yield. Its subunit molecular mass is ca 37 kDa. In this study, we determined the basic kinetic properties of the frog muscle enzyme. FBPase exhibited a maximum activity at pH 7.5. Like other FBPases the frog enzyme requires magnesium ions for its activity (K(a)=263 microM) and is activated by potassium ions (K(a)=63.6 microM). I(0.5) for calcium ion (91 microM) is 100 times higher than the corresponding value of mammalian muscle FBPase. K(s) for the substrate was 1.68 microM. Substrate excess inhibited the enzyme (K(si)=55 microM). AMP and fructose-2,6-bisphosphate (Fru-2,6P(2)) are potent inhibitors of frog muscle FBPase with I(0.5) of 0.2 microM and K(i) of 114 nM, respectively. Both inhibitors act synergistically on the frog muscle FBPase. In the presence of 0.05-0.5 microM of AMP, K(i) for Fru-2,6P(2) is 92 and 28 nM. I(0.5) for AMP for P. esculentus muscle FBPase is 55 times lower than the corresponding value for P. esculentus liver isozyme.

Effect of leaf position on levels of the chloroplast and cytosolic fructose bisphosphatase isozymes in the pea leaf nucleus

Immunocytolocalization experiments indicate that nuclear levels of the pea leaf cytosolic fructose bisphosphatase are higher in leaves located near the base of the plant and lower in expanded leaves at the apex. It seems possible that the cytosolic isozyme in the nucleus has a role in tissue aging. In contrast, there is no indication that leaf position or tissue age affects levels of the chloroplastic enzyme in the nucleus. The density of the chloroplast fructose bisphosphatase is higher in the nucleolus than in the nucleoplasm. Conversely, the density of the cytosolic isozyme is slightly higher in the nucleoplasm. Analysis of double immunolabeling experiments indicates that both isozymes are distributed nonrandomly with respect to DNA, and therefore colocalized with DNA, in the nucleus, and that the chloroplast isozyme is also distributed nonrandomly with respect to DNA in the chloroplast.

Subcellular localization of muscle FBPase in carp (Cyprinus carpio) tissues

Subcellular localization of muscle FBPase-a regulatory enzyme of glyconeogenesis-was investigated in carp using immunohistochemistry and protein exchange method. Results of the experiments revealed that, in striated muscles, FBPase associates with alpha-actinin of the Z-line and co-localizes with aldolase. Additionally, in cardiac and smooth muscle cells FBPase is present inside the nuclei. In the light of findings on mammalian muscle FBPase, the data presented here indicates that interaction of the enzyme with specific cellular partners and nuclear presence of FBPase is a general phenomenon in contemporary vertebrates.

F-actin, beta-tubulin, aldolase, and fructose-1,6-bisphosphatase in heteropteran ovarioles--I. Immunocytochemical investigations of whole-mounted ovarioles

The distribution of F-actin, beta-tubulin, aldolase, and fructose-1,6-bisphosphatase (FBPase) in ovarioles of four heteropteran species (Ilyocoris cimicoides, Coreus marginatus, Lygus pratensis, and Notostira elongata) was investigated biochemically and immunocytochemically. Aldolase was found to be uniformly distributed in the cytoplasm of trophocytes and follicular cells, with the highest concentration in prefollicular cells. Its concentration in follicular cells increased during differentiation and reached a peak in ovarian follicles at the stage of late choriogenesis. FBPase was observed in the cytoplasm (weak reaction) and on cell borders (strong reaction) of both germ line and somatic cells. No FBPase or aldolase signal was observed on the F-actin trophic core mesh or on stress fibers.