Properties of o-diphenol: O2 oxidoreductase from Musa cavendishii

Banana fruits (Musa cavendishii) contain a non-particulate o-diphenol: O₂ oxidoreductase that has been partially purified. The enzyme is inactivated during its catalytic action with a half time of 135 sec. The activation energy for the catalytic process is 4445 cal/mol. Classical thermal denaturation takes place only above 70°, with an entropy change of about 190 cal/mol °K at pH 6·0.     

A tetracyclic triterpenoid from Musa paradisiaca

The structure of a new tetracyclic triterpene isolated from the flowers of Musa paradisiaca was determined as (24R)-4α,14α,24-trimethyl-5α-cholesta-8,25(27)-dien-3β-ol.     

Multiple forms of starch phosphorylase from banana leaves

Two forms (A and B) of starch phosphorylase were found in the mature banana leaf by polyacrylamide gel electrophoresis and DEAE-cellulose chromatography. The young leaf contained only form A and the appearance of form B with leaf development was accompanied by a decrease in the content of form A. At a later stage of leaf maturity only form B could be found. The MWs of forms A and B were 450 000, and 220 000 respectively.     

Studies on invertase from Mangifera indica

There are two types of invertase in mango tissues, one active at 0° and the other at 37°. These invertases have been partially purified and some of their properties studied.     

Upsurge of particulate peroxidase in ripening banana fruit

Peroxidase was isolated from the pulp of ripening banana fruit and assayed with o-dianisidine as hydrogen-donor. Cell macerates contained soluble and particle-bound peroxidase. Soluble peroxidase levels did not appreciably differ in pre-climacteric, climacteric and post-climacteric fruit. Particulate peroxidase levels increased 3-fold with the initiation of the respiration climacteric and gradually declined with the onset of senescence. Bound peroxidase was released from cell wall and membrane fractions with washing in 0–8 M CaCl₂.     

Carbohydrate metabolism in Musa paradisiaca

Considerable variations exist in the content of glucose, fructose, sucrose, starch and protein and in the activities of enzymes involved in carbohydrate metabolism between different parts of the banana plant (Musa paradisiaca). Sucrose synthetase is present in the highest concentration in rootstock and fruit pulp, and sucrose phosphate synthetase in the pseudostem. The highest ratio of the activity of sucrose phosphate synthetase to sucrose synthetase is found in leaves. Acid invertase is present in leaves, leaf-sheath and fruit pulp and is not demonstrable in rootstock and pseudostem. Neutral invertase activity is high in pseudostem and leaf-sheath. Starch phosphorylase is largely concentrated in fruit pulp and rootstock. The maximum activity of ATP:d-phosphoglucose (ADPG) pyrophosphorylase is found in rootstock. β-Amylase is not demonstrable in rootstock and is largely concentrated in leaf-sheath. Hexokinase is most active in rootstock and the lowest in leaves. Acid phosphatase and alkaline phosphatase activity is highest in fruit pulp and pseudostem. Glucosephosphate isomerase is most active in the rootstock and lowest in the leaves.     

Physiological activators of invertase from Hevea brasiliensis latex

Potassium or sodium nitrates or phosphates, and thiols such as reduced glutathione or cysteine, stimulate the activity of invertase from Hevea brasiliensis latex. These activators raise the V_max but do not affect the K_m of the enzyme for sucrose. The action of these effectors is additive. Their efficiency is pH dependent, being higher below pH 7.0 and markedly decreasing above it.     

Extracellular invertase from Aspergillus flavus

An extracellular invertase was induced in cultures of Aspergillus flavus Link during growth in liquid medium that contained sucrose as the sole carbon source. Synthesis of this enzyme was repressed by the addition of glucose or fructose to sucrose-metabolizing cells, and was induced in a glucose or fructose-metabolizing culture by the addition of sucrose. A. flavus invertase had a pH optimum of 6.0 and an apparent Km of approximately 133 mM for sucrose. The enzyme required potassium phosphate for maximum activity, optimum concentration being 250 mM. The enzyme was partially purified by ammonium sulphate precipitation followed by dialysis and separated by molecular exclusion into three components with molecular weights ranging from approximately 40,000 to 55,000.     

Volatile components of banana pseudostem of a cultivar susceptible to the banana weevil

Volatiles from banana (‘githumo’'cultivar) pseudostem were trapped using porapak S. The trapped volatiles were desorbed from porapak columns by elution with dichloromethane and analysed using GC and GC-MS. The volatile compounds identified included -pinene, β-pinene, β-myrcene, limonene, -cubebene, -copaene, -cedrene, β-caryophyllene and -humulene.     

Stimulation of maize invertase activity following infection by Ustilago maydis

The effect of U. maydis infection on the invertase activity of maize leaves has been studied. Infection causes a specific stimulation of an acid invertase in soluble and pellet fractions of homogenized tissue. Invertase activity is stimulated within one day after infection, and is maintained at a high level until 10 days after infection, in contrast to the progressive decline in activity with age, in healthy leaves. Analyses of soluble extracts by gel electrophoresis suggest that the invertase showing this increase is derived from the host and not the pathogen.     

Constituents of Musa balbisiana seeds and their activity against Cryptolestes pusillus

The chloroform and acetone extracts of the seeds of Musa balbisiana Colla (Musaceae) and four of its constituents were assayed in the diet for toxicity against the flat grain beetle (Cryptolestes pusillus Schöherr). A mixture of fatty esters of phytol and the flavan (+)-epiafzelechin showed a significant growth inhibition and toxicity against this economically important pest of stored cereals. The LD₅₀ was 6.3% for the most active compound, (+)-epiafzelechin.     

Stimulation of the glyoxylate shunt in gamma-irradiated banana

Succinic dehydrogenase was the most susceptible among the TCA cycle enzymes to gamma irradiation in preclimacteric banana. Maximum inhibition occurred at the 3rd day after irradiation. Impairment of this activity did not affect operation of the TCA cycle, assessed from the incorporation pattern of acetate [2-¹⁴C] into the organic acids such as citric, malic and succinic. Nevertheless, incorporation into keto acids like glyoxylate, α-keto-glutarate and oxaloacetate showed a difference. The rate of labelling into α-ketoglutarate and oxaloacetate was reduced on the 3rd day while incorporation into glyoxylate was increased indicating the operation of glyoxylate shunt pathway. Studies on the individual enzymes of this pathway, isocitrate lyase and malate synthetase confirmed its operation. The reduction in oxalo-acetate has been attributed to the increased gluconeogenesis.     

Purification and characterization of extracellular invertase from the hypocotyls of mung bean (Phaseolus radiatus L.)

The extracellular invertase (β-D-fructofuranoside fructohydrolase, EC 3.2.1.26) was isolated and characterized from the hypocotyls of mung bean (Phaseolus radiatus L.). The enzyme was purified to apparent homogeneity by ammonium sulfate fractionation and sequential chromatography over diethylaminoethyl (DEAE)-cellulose anion exchange, Concanavalin (Con) A-Sepharose 4B affinity and Sephadex G-200. The overall purification was about 77-fold with a recovery of about 11%. The finally purified enzyme exhibited a specific activity of about 113 μmol of glucose produced mg^-1 protein min^-1 at pH 5.0 and appeared to be a single protein by nondenaturing polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate (SDS)-PAGE. The enzyme had the native molecular mass of 134 kD and subunit molecular weight of 67 kD as estimated by Sephadex G-200 chromatography and SDS-PAGE, respectively, suggesting that the enzyme was composed of homodimeric proteins. On the other hand, the enzyme appeared to be a glycoprotein containing mannosyl residues on the basis of its ability to interact specifically with the immobilized Con A and the separability of invertase-Con A complex by methyl-α-D-mannopyranoside. The enzyme had a K_m for sucrose of 3.4 mM and its pH optimum of 4.0. The enzyme showed highest enzyme activity with sucrose as substrate. Raffinose and cellobiose were hydrolyzed at a low rate, maltose and lactose were not cleaved by the enzyme. These results indicate the extracellular invertase is a β-fructofuranosidase.     

Acid invertase in germinating Lactuca sativa seeds: Evidence for de novo synthesis

Acid invertase activity in germinating lettuce seeds is first observed after 15 hr germination, from when it rises steadily at least till 30 hr of germination. The enzyme was purified about 500-fold using ammonium sulphate fractionation followed by isoelectric focussing. Labelling the enzyme with ³⁵SO₄ or leucine-¹⁴C during development of its activity, followed by purification suggests that acid invertase is synthesized de novo during germination. The possible significance of acid invertase in the metabolism of the seed is discussed.     

Purification and characterization of two soluble acid invertase isozymes from Japanese pear fruit

Two isozymes (AIV I and AIV II) of soluble acid invertase (EC 3.2.1.26) were purified from Japanese pear fruit through procedures including (NH(4))(2)SO(4) precipitating, DEAE-Sephacel column chromatography, Concanavalin A (ConA)-Sepharose affinity chromatography, hydroxyapatite column chromatography and Mono Q HR 5/5 column chromatography. The specific activities of purified AIV I and AIV II were 2670 and 2340 (nkat/mg protein), respectively. AIV I was a monomeric enzyme of 80 kDa, while AIV II may be also a monomeric enzyme, which is easy to be cleaved to 52 kDa and 34 kDa polypeptide during preparation by SDS-PAGE. The Km values for sucrose of AIV I and AIV II were 3.33 and 4.58 mM, respectively, and optimum pH of both enzyme activities was pH 4.5.     

Identification of multiple forms of phosphofructokinase in ripening dwarf cavendish banana

The levels of six glycolytic intermediates and the activity of phosphofructokinase (PFK) were determined in Dwarf Cavendish banana at different stages of ripening between harvest and senescence. There was a 2.3-fold increase in the level of fructose- 1,6-diphosphate between the preclimacteric and climacteric peak stage. The PFK preparations from preclimacteric and climacteric peak stages were purified ca 15-fold using Blue-Sepharose affinity chromatography. The clectrophoretic studies with the enzyme preparations ofthese two stages ofripening indicated the presence of two forms of PFK at both stages of ripening.     

Acid invertase (sucrose hydrolysis) is not required for sucrose mobilization from the vacuole

The possible involvement of acid invertase (sucrose hydrolysis) as a prerequisite for sucrose mobilization from the vacuole of storage cells was investigated. Sugarcane ( Saccharum officinarum ) stalks, carrot ( Daucus carota ) roots and red beet ( Beta vulgaris ) hypocotyls were planted under greenhouse conditions and allowed to resume growth. The plants, however, were not permitted to become photosynthetically autotrophic by removing the new expanded leaves. Sucrose levels declined significantly in all three tissues without the development of acid invertase (EC 3.2.1.26) during the 21‐day experimental period. Acid invertase and thus sucrose hydrolysis within the vacuole was, therefore, not required for sucrose mobilization.     

Biochemical aspects of the developing and ripening banana

The peel and pulp of the banana fruit and the pseudostem were examined for glutamate-oxaloacetate transaminase (GOT), glutamate-pyruvate transaminase (GPT) and aldolase activities and protein, phenolics, chlorophyll and starch. The peel-pulp ratio at various stages of fruit development on the plant and in detached fruits showing incipient ripening were used as an index of the physiological age of the fruit. The enzymes exhibited maximum activity at a stage corresponding to the initiation of the climacteric. GPT level at this stage was higher than that of GOT. An initial increase in the protein content was followed by a decline in both peel and pulp, the level reaching a minimum in climacteric fruits. Astringency, measured in terms of total phenolics, decreased with development; in mature fruits, peel contained 4–5 × as much phenolics as pulp. Chlorophyll in mature fruits was 10 × higher than in young fruits and decreased in ripe fruits. The onset of ripening was attended with a pronounced decrease in the starch. The various analyses were carried out also on the pseudostem removed from the plant soon after flower formation.