Site of Synthesis of NADPH: Protochlorophyllide Oxidoreductase in Rye (Secale cereale)

The site of synthesis of the plastid membrane-located enzyme, protochlorophyllide reductase, has been determined. Plastid ribosome-deficient and normal rye (Secale cereale L., cv Rheidol) plants were grown in darkness at 33°C and 22°C, respectively. Extracts from these plants were analyzed for the levels of different ribosomal RNAs and cytochrome f and the activity of a number of enzymes with well-established sites of synthesis. The results confirmed that the higher temperature had induced a specific inhibition of protein synthesis in the plastids. The activity and level of protochlorophyllide reductase was unaffected by growth at the higher temperature, suggesting it to be a cytoplasmically synthesized enzyme.     

A microprocedure for extracting tissue nucleotides for analysis by high-performance liquid chromatography.

A method is described for the preparation of concentrated tissue extracts for nucleotideanalysis by high-performance liquid chromatography (hplc). Ten to one hundred milligrams of tissue was extracted in a combined weighing-homogenizing-centrifuge tube using a trichloracetic acid (TCA)-methanol extractant containing a radioactive internal standard. This extractant eliminated nucleotide interconversion which was found to occur when TCA alone was employed. High ATP/ADP and ATP/AMP ratios were observed and recoveries of greater than 97% were obtained with exogenous radioactive nucleotides. The method has been applied successfully in studies on muscle, heart, liver, kidney, lung, brain, and subcellular fractions.     

Meiosis in NEUROSPORA CRASSA. II. Genetic and Cytological Characterization of Three Meiotic Mutants

Three recessive meiotic mutants, asc(DL95), asc(DL243) and asc(DL879), were detected by the abortion of many of their ascospores and were analyzed using both cytological and genetic methods. Even though asc(DL95), asc (DL243) and the previously studied meiotic mutant, mei-1 (Smith 1975; Lu and Galeazzi (1978), complement one another in crosses, they apparently do not recombine (DeLange and Griffiths (1980). Thus, they may represent alleles of the same gene or comprise a gene cluster. Ascospore abortion in these mutants is caused by abnormal disjunction of meiotic chromosomes. In crosses homozygous for asc(DL95), asc(DL879) or mei-1, both pairing of homologs and meiotic recombination frequencies are reduced. In each case, this primary defect is followed by the formation of univalents at metaphase I and their irregular segregation. The mutant asc(DL243) has a defect in ascus formation, and later in disjunction during the second meiotic and post-meiotic divisions. The first-acting defect before or during karyogamy results in the abortion of most cells. Some cells manage to proceed past this block. During the second meiotic division, most chromosomes of the few resulting asci are attached to only one of the two spindle-pole bodies. Disjunction at the post-meiotic division is also highly irregular. This mutant appears to be defective in the attachment of one spindle-pole body to a set of chromosomes. The defect may involve either a centromere-associated product or a spindle-pole body.     

The control of the synthesis of isocitrate lyase in a thermophilic bacillus.

From a strain of Bacillus stearothermophilus, devoid of active pyruvate carboxylase, a mutant (NG-15) was selected that grew on acetate in the presence of glucose. This mutant differed from its parent organism in possessing high activities of isocitrate lyase when grown on all carbon sources tested except nutrient broth, in possessing unusually low activities of NADP+-dependent isocitrate dehydrogenase and in containing increased amounts of isocitrate. Revertants of mutant NG-15 which regained the ability to synthesize active pyruvate carboxylase also synthesized isocitrate lyase and isocitrate dehydrogenase to the same extent as the wild-type strain. These results suggest that the regulatory mechanism for the synthesis of isocitrate lyase in the thermophile may be different from that in mesophilic bacilli.     

Alkalinization of phosphorylase kinase-deficient muscle during tetanic contraction

The intracellular pH of resting and stimulated muscle was monitored by two independent methods: measurement of pH iniodacetate-treated homogenates of freezeclamped tissue and the absorbance at 550–443 nm of intracellular neutral red dye in vivo. During tetanic stimulation, muscle of phosphorylase kinase-deficient mice shows a transient alkalinization whereas muscle in normal mice becomes more acid under similar conditions. The alkalinization appears to be caused by abnormally rapid AMP deamination associated with adaptation to phosphorylase kinase deficiency.     

The cytochromes of Acanthamoeba castellanii.

1. Low-temperature difference spectra of gradient-purified mitochondria of Acanthamoeba castellanii reveal the presence of cytochromes b-555, b-562 and c-549, with a-type cytochromes having a broad asymmetrical maximum at 602 nm; these components were also observed in specta of whole cells. 2. The a-type cytochromes are unusual in that they have split Soret absorption maxima (at 442 and 449 nm) and an uncharacteristic CO difference spectrum. 3. CO difference spectra of whole cells and 'microsomal' membranes show large amounts of cytochrome P-420 compared with cytochrome P-450. 4. Difference spectra in the presence of cyanide indicate the presence of an a-type cytochrome and two cyanide-reacting components, one of which may be cytochrome a3. 5. Whole-cell respiration in a N2/O2 (19:1) atmosphere was decreased by 50%, suggesting the presence of a low-affinity oxidase. This lowered respiration is inhibited by 50% by CO, and the inhibition is partially light-reversible; photochemical action spectra suggest that cytochrome a3 contributes to this release of inhibition. Other CO-reacting oxidases are also present. 6. The results are discussed with the view that cytochrome a3 is present in A. castellanii, but its identification in CO difference spectra is obscured by other component(s).     

Intracellular transport and localization of major histocompatibility complex class II molecules and associated invariant chain

The intracellular transport and location of major histocompatibility complex (MHC) class II molecules and associated invariant chain (Ii) were investigated in a human melanoma cell line. In contrast to the class II molecules, which remain stable for greater than 4 h after synthesis, the associated Ii is proteolytically processed within 2 h. During or shortly after synthesis the NH2-terminal cytoplasmic and membrane-spanning segment is in some of the Ii molecules cleaved off; during intracellular transport, class II associated and membrane integrated Ii is processed from its COOH terminus in distinct steps in endocytic compartments. Immunocytochemical studies at the light and electron microscopic level revealed the presence of class II molecules, but not of Ii on the cell surface. Intracellularly both Ii and class II molecules were localized in three morphologically and kinetically distinct compartments, early endosomes, multivesicular bodies, and prelysosomes. This localization in several distinct endosomal compartments contrasts with the localization of class II molecules in mainly one endocytic compartment in B lymphoblastoid cell lines. As in these lymphoblastoid cell lines Ii is known to be rapidly degraded it is conceivable that the rate of proteolysis of the class II associated Ii and its dissociation from class II molecules modulates the retention of the oligomeric complex in endocytic compartments, and as a consequence the steady-state distribution of these molecules within the endosomal system.     

Distribution of newly synthesized lysosomal enzymes in the endocytic pathway of normal rat kidney cells

We have investigated the distribution of newly synthesized lysosomal enzymes in endocytic compartments of normal rat kidney (NRK) cells. The mannose-6-phosphate (Man6-P) containing lysosomal enzymes could be iodinated in situ after internalization of lactoperoxidase (LPO) by fluid phase endocytosis and isolated on CI-MPR affinity columns. For EM studies, the ectodomain of the CI-MPR conjugated to colloidal gold was used as a probe specific for the phosphomannosyl marker of the newly synthesized hydrolases. In NRK cells, approximately 20-40% of the phosphorylated hydrolases present in the entire pathway were found in early endocytic structures proximal to the 18 degrees C temperature block including early endosomes. These structures were characterized by a low content of endogenous CI-MPR and were accessible to fluid phase markers internalized for 5-15 min at 37 degrees C. The bulk of the phosphorylated lysosomal enzymes was found in late endocytic structures distal to the 18 degrees C block, rich in endogenous CI-MPR and accessible to endocytic markers internalized for 30-60 min at 37 degrees C. The CI-MPR negative lysosomes were devoid of phosphorylated hydrolases. This distribution was unchanged in cells treated with Man6-P to block recapture of secreted lysosomal enzymes. However, lysosomal enzymes were no longer detected in the early endosomal elements of cells treated with cycloheximide. Immunoprecipitation of cathepsin D from early endosomes of pulse-labeled cells showed that this hydrolase is a transient component of this compartment. These data indicate that in NRK cells, the earliest point of convergence of the lysosomal biosynthetic and the endocytic pathways is the early endosome.