MITOCHONDRIAL—ASSOCIATED CDP—DIACYLGLYCEROL SYNTHASE ACTIVITY IN GERMINATING SOYBEANS

The mitochondrial-associated CTP: phosphatidic acid cytidylyltransferase (CDP-diacylglycerol synthase, EC 2.7.7.41) was studied from germinating soybeans. The enzyme exhibited a broad pH optimum between pH 6.5 and pH 8.0. Activity was dependent on the addition of magnesium ions (20 mM) and the nonionic detergent Triton X-100 (5 mM). The apparent K_m values for CTP and phosphatidic acid were 0.58 mM and 0.12 mM, respectively. A V_max of 0.12 U/mg was found for the mitochondrial-associated enzyme. Phospholipids generally stimulated activity while ADP and CDP strongly inhibited activity. Thiore-active agents inhibited activity indicating that a sulphydryl group is essential for activity. The enzyme was thermally inactivated at temperatures above 35°C.     

HOSPHATIDYLGLYCEROPHOSPHATE SYNTHASE FROM GERMINATING SOYBEANS1

Phosphatidylglycerophosphate synthase (CDP-diacylglycerol: sn-glycerol-3-phosphate phosphatidyltransferase, EC 2.7.8.5) activity was identified from the crude mitochondrial fraction of germinating soybeans. The mitochondrial enzyme exhibited pH optima at 7.0 and 9.5. Phosphatidylglycerophosphate was the predominate product at pH 9.5 while phosphatidylglycerol was the predominate product at pH 7.0. At pH 9.5, maximum phosphatidylglycerophosp-hate synthase activity was dependent on manganese (0.5 mM), magnesium (10 mM), or cobalt (20 mM) ions and Triton X-100 (0.5 mM). The apparent K_m values for CDP-diacylglycerol and glycerol-3-phos-phate were 0.1 mM and 0.17 mM, respectively. Activity was completely stable to temperatures up to 70°C and the energy of activation was 3.16 Kcallmole. Thioreactive agents slightly inhibited activity.     

KINETIC PROPERTIES OF PHOSPHATIDYLINOSITOL SYNTHASE FROM GERMINATING SOYBEANS

ABSTRACT CDP-1,2-diacyl-sn-glycerol (CDP-diacylglycerol): myo-inositol phosphatidyltransferase (EC. 2.7.8.11) catalyzes the final step in the de novo synthesis of phosphatidylinositol in the microsome fraction of germinating soybeans. The Michaelis constants for CDP-diacylglycerol and myo-inositol were determined for the reaction using a Triton X-100-CDP-diacylglycerol mixed micelle substrate. The K_mvalues for CDP-diacylglycerol and myo-inositol were 30μM and 0.11 mM, respectively.     

SUBCELLULAR LOCALIZATION OF PHOSPHATIDYLINOSITOL SYNTHASE FROM GERMINATING SOYBEANS

ABSTRACT CDP-1,2-diacyl-sn-glycerol: myo-inositol phosphatidyltransferase (EC. 2.7.8.11, phosphatidylinositol synthase) catalyzes the final step in the de novo synthesis of phosphatidylinositol. The subcellular localization of this enzyme from germinating soybeans was determined by differential centrifugation and sucrose gradient centrifugation. Differential centrifugation of the crude extract indicated that phosphatidylinositol synthase activity was primarily located in the fraction sedimenting between 12,000 ×g and 100,000 ×g. Sucrose gradient centrifugation of the crude extract indicated that phosphatidylinositol synthase was associated with the endoplasmic reticulum.     

大豆中的天然抗氧化物质

综述了大豆中的天然抗氧化物质的种类,含量和抗氧化性能及它们对人体的保健作用。     

THE DISTRIBUTION OF WATER IN GERMINATING BARLEY

During germination, the embryo of barley absorbs water initially from the film surrounding the corn and later from the endosperm. If growth is stimulated during steeping, absorption of water by the embryo modifies the pattern of moisture distribution and this is usually associated with reduced extractability in the final malt.     

LIPOLYTIC ACTIVITY OF ENZYMES FROM GERMINATING SEEDS OF SESAME (SESAMUM INDICUM L.)

Sesame ( Sesumum indicum ) seeds were germinated for seven days under laboratory conditions and the lipolytic activity of the defatted, dried seedlings was determined. Germination increased the lipolytic activity of sesame seeds and the highest activity was observed on day-4. The lipases of four days germinated sesame seeds were able to hydrolyze mainly the saturated fatty acids from seal blubber oil (SBO). Reaction temperature, incubation period and oil-to-seedling powder ratio had a significant effect on the hydrolysis of saturated fatty acids, thereby concentrating unsaturated (mono- and polyunsaturated) fatty acids of seal blubber oil.     

CELLULASES OF PLANT AND MICROBIAL ORIGIN IN GERMINATING BARLEY

Cellulase activity in crude extracts of germinating barley is at least five-fold higher in hulled than in hull-less cultivars. Surface sterilization of the grain prior to germination reduces cellulase to levels that are similar in all cultivars. In hulled barley most of the cellulase detected during germination is probably of microbial origin, but there is circumstantial evidence to suggest that significant activity can also be attributed to cellulases of plant origin. The micro-organisms associated with germinating grain reside largely in the hull and the major fungal species present on the hulled variety Clipper were Aureobasidium pullulans, Rhizopus stolonifer and Penicillium spp. Surface sterilization of the grain with silver nitrate, followed by steeping in a solution containing antibiotics, completely eliminated microbial growth on hull-less cultivars. After similar treatment of a hulled barley two yeasts could be detected. The results emphasize the importance of eliminating microbial growth prior to studies of polysaccharide hydrolases which develop during the germination of barley and which are assumed to be of plant origin.     

THE UPTAKE AND DISTRIBUTION OF BROMATE IN GERMINATING BARLEY

Bromate applied to steeped barley enters the grain rapidly, within 4 h of application; it is reduced to bromide as germination proceeds but persists in the endosperm in measurable quantities until kilning. Bromate has not been detected in kilned malt. Examination of lateral sections of grain shows that bromate concentration is highest at the embryo end, lowest in the middle and has an intermediate concentration at the distal end. These results, obtained with selected undamaged grains of both Proctor barley and Nackta (a naked variety), suggest that bromate can enter the grain at the distal end and over the grain surface as well as through the embryo.     

THE DETERMINATION AND UTILIZATION OF GIBBERELLIC ACID IN GERMINATING BARLEY

A barley endosperm bioassay, utilizing the induction of acid phosphatase in barley endosperm seed halves, has been developed and applied to study both the development of endogenous gibberellin in grain germinating under malting conditions and the utilization of externally applied gibberellic acid. The assay is affected by barley age and variety and these observations may have practical implications. After 24 h germination the level of endogenous gibberellin-like material present in the grain was approximately 1·4 ng/corn. The biological activity of the total gibberellin-like material extracted from grain treated with gibberellic acid fell during germination although significant quantities of applied gibberellic acid had entered the grain during the first 24 h germination.     

THE ROLE OF PROLINE IN THE AMINO ACID METABOLISM OF GERMINATING BARLEY

The changes in nitrogen composition in germinating barley have been studied under malting conditions. It has been shown that most amino acids are produced in the endosperm, by peptidase activity, in the correct concentrations required for protein synthesis in the embryo. During growth the total concentrations of free and combined glutamic acid, glycine and ammonia decrease with the concurrent increases in the total concentration of free and combined proline, aspartic acid and lysine. No evidence has been found for the presence of an end product inhibition of peptidase activity in the endosperm. Thus in malting the growth of the embryo is shown to serve a useful purpose in the removal of amino acids from the endosperm.     

MODIFIED ASSAY FOR α-AMYLASE IN GERMINATING BARLEY

The activity of α-amylase is defined as the reciprocal of the time taken by a heat-treated malt extract to reduce the iodine-colouring capacity of a solution of soluble starch to half its initial value, under standardized conditions. Reasons are given for preferring starch iodine colour to reducing power measurements for following enzyme activity. α-Amylase is extracted from grain and contaminating enzymes are largely inactivated by heating a pulverized sample in a solution of calcium acetate. Boiled extracts of coloured malt make solutions of α-amylase less stable to heat. Precautions taken to achieve accurate sampling of enzyme digests and in measuring the starch iodine colour usefully improve the precision of the method. Results are calculated graphically using standard graph principles.