Higher Plant Enzyme Research Articles

Purification and properties of alliin lyase from the fungus Penicillium corymbiferum

Penicillium corymbiferum contains alliin lyase (cysteine sulfoxide lyase; alliin alkyl sulfenate-lyase, EC 4.4.1.4). This appears to be the first report of such an enzyme being isolated from a fungus. A 45-fold purification in two steps was effected by taking a 40–65% (NH 4) 2SO 4 cut from a mycelial homogenate and chromatographing it, after dialysis, on Sephadex G-200. The resulting preparation required pyridoxal phosphate, had an apparent K m using alliin ( S- allyl- l-cysteine sulfoxide ) as a substrate of 5.8 mM, did not utilize S-alkylcysteines, and had a pH optimum of 6.5. These properties are similar to those of alliin lyase from garlic. It differed from this higher plant enzyme in that it had relatively little activity at pH 8.0, and was not stimulated by divalent ions or EDTA.

Studies on Mutarotases: I. PURIFICATION AND PROPERTIES OF A MUTAROTASE FROM HIGHER PLANTS

Abstract The enzyme mutarotase (aldose 1-epimerase), found in most mammalian tissues and certain bacteria, catalyzes interconversion of the anomeric forms of certain sugars, particularly those pentoses and hexoses related configurationally to d-glucose. This paper describes the widespread distribution of a similar enzyme in higher plants. The enzyme was found in both mono- and dicotyledons and was most widely distributed in the families Solanaceae (bell pepper, red pepper, tomato, eggplant), Cucurbitaceae (cantaloupe, cucumber, squash), and Liliaceae (asparagus, hyacinth, tulip). It was absent from all tested members of the Rutaceae (lime, lemon, orange, grapefruit) and Rosaceae (plum, pear, apple, strawberry). The mutarotase from green pepper (Capsicum frutescens) was isolated and purified approximately 1400-fold by a combination of salt fractionation, dialysis, preferential protein stabilization, and column chromatography on hydroxylapatite and diethylaminoethyl cellulose. The substrate specificity, in order of decreasing catalytic efficiency (d-glucose = 100), was d-galactose, 150; l-arabinose, 49; d-xylose, 18; and maltose, 6. The Km for d-glucose was 23.5 mm. Maltose, l-arabinose, and cellobiose were effective competitive inhibitors (Ki = 3.1, 6.3, and 12.3 mm, respectively). Phloridzin, phloretin, l-fucose, and l-deoxyglucose did not inhibit plant mutarotase. This is in marked contrast to the inhibitor specificity of the mammalian enzyme. The temperature optimum was 40°, and a broad pH-activity spectrum was displayed from pH 4.0 to 8.5, with the maximum at pH 7.4. The enzyme activity sedimented as a single band in sucrose density gradients and was eluted as a single peak from chromatographic columns. The molecular weight is approximately 50,000, and the turnover number is in excess of 8 x 105 moles of α- to β-glucose per min. The enzyme is sulfhydryl-dependent, being completely inactivated by 2 x 10-5 m mercuric chloride and reactivated by cysteine. A rapid, semiautomated assay procedure for the enzyme is also described.

Orotidine-5'-phosphate decarboxylase and pyrophosphorylase of bean leaves.

This report includes results demonstrating the existence of orotidine-5'-phosphate decarboxylase and orotidine-5'-phosphate pyrophosphorylase in plant leaves. The decarboxylase enzyme, purified 8 fold from leaves of etiolated pinto beans (Phaseolus vulgaris L.), had a pH optimum of 6.3. It was strongly inhibited by 6-azauridine-5'-phosphate; a concentration of 12 mum decreased the reaction rate 60%. The enzyme was not dependent upon magnesium ions or inhibited by p-chloromercuribenzoate. It was present in other parts of the bean plant and was found in young leaves of tomato (Lycopersicon esculentum Mill.) and Canada thistle (Cirsium arvense L.)The enzyme orotidine-5'-phosphate pyrophosphorylase, which catalyzes the formation of orotidine-5'-phosphate from orotic acid and 5-phosphoribosyl-1-pyrophosphate, was found in the etiolated bean leaves, and was also present in the leaves of tomato and Canada thistle. It was stimulated by manganous or magnesium ions and had a pH optimum of 7.2. The K(m) value obtained by varying the concentrations of 5-phosphoribosyl-1-pyrophosphate was 75 mum, and when orotic acid was varied the resulting K(m) was 3.5 mum. The presence of these 2 enzymes in higher plants, combined with previous results with inhibitors and labeled metabolites, indicates that the normal pathway of pyrimidine nucleotide synthesis in higher plants proceeds through orotic acid and OMP.

Mutarotase in higher plants: distribution and properties.

The enzyme mutarotase from mammalian tissues catalyzes interconversion of anomeric forms of glucose and structurally related sugars; it may be involved in transport of sugars. Isolation and species distribution of a similar enzyme in higher plants are described. The enzyme from green pepper (Capsicum frutescens) was purified 230-fold. It differs from the mammalian enzyme in both substrate specificity and lack of inhibition by 1-deoxyglucose and phloridzin.

The formation of guanosine diphosphate d-glucose by enzymes of higher plants

The formation of guanosine diphosphate d-glucose by enzymes of higher plants

Indoleacetic Acid Oxidizing Enzyme & Inhibitors from Light-Grown Cotton

As one aspect of a study of abscission in the cotton plant, we have been interested in the possible presence of an indoleacetic acid (IAA) oxidase in the aerial portions of the green plant. The need for investigation was indicated by the possibility that IAA oxidase could affect the decline in detectable auxin in cotton which occurs just prior to leaf fall (1, 2). A study was initiated after noting that although there is evidence for the occurrence of IAA in cotton (3, 12), a preliminary attempt to demonstrate IAA oxidase was unsuccessful (13). Furthermore, information on the occurrence of the enzyme in other -green tissues was relatively limited and an unequivocal function of the enzyme in higher plants has not been clearly established. This paper presents evidence for the occurrence of an IAA oxidase in cotton and some characteristics of the enzyme and an inhibitor(s).

Adaptive Synthesis of Nitrate Reductase in Higher Plants

ADAPTIVE production of enzymes in higher plants is not widely recognized, although two examples have been reported1. Nitrate reductase systems are adaptive to nitrate and nitrite in micro-organisms2,3 and studies with cauliflower4 have suggested a similar adaptive character in higher plants. Tang and Wu5 obtained more direct evidence of the adaptive character of this enzyme in rice seedlings germinated for five days under sterile conditions and Rijven6 reported similar results for wheat embryos germinated for 24 hr. These experiments, however, involved relatively prolonged periods of contact between inducer and tissues undergoing both rapid cell division and expansion.