Identification and genetic control of starch-degrading enzymes in maize endosperm

Three starch-degrading enzymes from liquid endosperm of maize have been separated by means of horizontal acrylamide gel electrophoresis. The three enzymes are tentatively identified as -amylase (zone 1), -amylase (zone 2), and -glucan phosphorylase (zone 3). Electrophoretic variants of these enzymes were found among ten inbred strains examined. Results of genetic crosses with respect to zone 2 amylase show that it is controlled by a pair of alleles (Amy-2 ^A and Amy-2 ^B) acting without dominance. It further appears that Amy-2 and Ct (catalase) are linked with 5% recombination frequency.This work was supported by the U.S. Atomic Energy Commission, under contract No. AT(11-1)-1338.     

SIEVE TUBES AND CALLOSE IN ELODEA LEAVES

Detachment and incubation of Elodea leaves promoted callose synthesis in all cells, especially in epidermal pits and in sieve tubes. Phloem was detected in the midrib by fluorescent staining of callose induced to form on sieve plates. In EM views of mature sieve elements nucleus and tonoplast were lacking, mictoplasm replaced cytoplasm, mitochondria were fewer in number, and large plastids contained crystalline inclusion bodies. Slime was present as compact aggregates and as individual fibrils in mictoplasm and sieve pores. Deposition of callose is considered in relation to the blockage concept of callose function.     

云南10个民族红细胞酸性磷酸酶型分布调查

用淀粉凝胶电泳法对云南省汉族及9个少数民族的红细胞酸性磷酸酶(ACP_1)的表型分布进行了调查,检出A、BA和B3种表型,计算得云南汉、彝、白、傣、瑶、佤、哈尼、布朗、基诺和拉祜族ACP_1~A、ACP_1~B的基因频率依次为0.2067、0.7933;0.2406、0.7594;0.2341、0.7659;0.3750、0.6250;0.2300、0.7700;0.2727、0.7273;0.3594、0.6406;0.3036、0.6964;0.2381、0.76119和0.4474、0.5526。未发现ACP_1~C基因及其它稀有基因。研究表明,ACP_1表型的分布存在着一定的种族与民族差异。     

大肠杆菌棉子糖操纵子α—半乳糖苷酶表达的调节控制

The alpha-galactosidase, coded for by the first structural gene rafA in the plasmid determined raf operon was an inducible enzyme. In contrast to lac or mel operon, raf operon has more strict structural specificity for inducers. The enzyme can be induced by melibiose and raffinose, or weakly by D-galactose, but not by structurally related sugars such as lactose, PNPG etc.. The alpha-galactosidase forming capacity as function of growth curve reached a single peak at the end of the logarithmic phase of the growth. The structure and regulation of raf operon is similar to those of lac operon. The repressormor-mediated negative control plays a major role in the regulation of raf operon, and cAMP-CAP mediated positive control is also involved in the regulation. When 0.4% glucose was added into the medium with other carbon sources, the expression of the enzyme was repressed by 2-3 fold. Transient catabolite repression has been observed neither in inducible nor constitutive alpha-galactosidase expression. Based on alpha-galactosidase assay, in mutant strains CA8306(cya) and CA8445 (cya, crp) the expression level of raf operon was only 9% and 2.5% of that in wild type strain respectively. The glucose effect or the repression in cya mutant can be abolished by 1-5 mmol cAMP. The constitutive alpha-galactosidase expression in cya and cry double mutant (CA8445) remains repressible by glucose, but irreversible by cAMP, suggesting cAMP-CAP complex is not the exclusive mediator of the catablite repression.(ABSTRACT TRUNCATED AT 250 WORDS)     

The 6S- and 6R-diastereomers of 5, 10-dideaza-5, 6, 7, 8-tetrahydrofolate are equiactive inhibitors of de novo purine synthesis

The diasteromers of 5,10-dideaza-5,6,7,8-tetrahydrofolate (DDATHF) differing in chirality about carbon 6 were resolved and studied as inhibitors of folate-dependent processes in mouse leukemia cells. Both diastereomers of DDATHF were found to be potent inhibitors of leukemia cell growth due to effects on de novo purine synthesis. Cell growth inhibition by these compounds was prevented by 5-formyltetrahydrofolate in a dose-dependent manner. This indicated that the effects of the DDATHF diastereomers were due to inhibition of folate-dependent processes. Metabolite reversal experiments indicated that 5'-phosphoribosylglycinamide formyltransferase was the major site of action of these compounds in mouse cells. Another site in de novo purine synthesis was affected at higher concentrations of diastereomer B in L1210 cells. Low concentrations of both diastereomers were found to inhibit pure L1210 5'-phosphoribosylglycinamide formyltransferase competitively with the folate substrate. The two diastereomers were also efficient substrates for mouse liver folylpolyglutamate synthetase. We conclude that the 6R- and 6S-diastereomers of DDATHF are remarkably similar and equiactive antimetabolites inhibitory to de novo purine synthesis and that the biochemical processes involved in their cytotoxicity display little stereochemical specificity.     

Structure and function of human hemoglobin covalently labeled with periodate-oxidized adenosine triphosphate

Periodate-oxidized adenosine triphosphate (o-ATP), a ribose ring-opened dialdehyde derivative of ATP, reacts specifically with human deoxyhemoglobin to give a single major covalently modified product after reduction with sodium borohydride. This product, designated di-ATP Hb, was isolated using ion-exchange chromatography and shown to have incorporated two molecules of o-ATP/tetramer. Peptide mapping and x-ray crystallography at 2.8-A resolution indicate that a covalent adduct is formed between the ligand and residues Lys-82 EF6 of each beta chain in the organic phosphate-binding site of the molecule. di-ATP Hb exhibits a significantly decreased oxygen affinity (P50 = 20.8 mm Hg versus 5.8 mm Hg control; 50 mM 2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)-propane-1,3-diol, pH 7.4, 0.1 M C, 20 degrees C). The subunit cooper-activity of di-ATP Hb is also reduced (nmax = 1.9 versus 2.7 control).