P. S. Krishnan

Glucan phosphorylase in the leaves of Dendrophthoe falcata: Purification and characterization of enzyme

Abstract α-Glucan phosphorylase of the leaf tissues of D. falcata was partially purified and isolated in two forms, A and B, by DEAE-cellulose column chromatography. Both the forms utilized soluble starch with equal efficiency, the K m value being 0·12 and 0·25 g/l for A and B respectively. Form A phosphorylase utilized glycogen efficiently, with K m value of 0·42 g/l but glycogen did not serve as primer for the B form. In contrast, the B form alone could utilize achroic dextrin, though with less efficiency than starch. The K m values for glucose-1-phosphate were 5 mM and 1·7 mM for A and B. AMP activated phosphorylase A, at the optimum pH, but not the B form. Among other differences between the two enzyme fractions were stability towards heat, linearity of activity with protein concentration and response to added cations and mercaptoethanol. The two enzymes were sensitive to some phenolics; phloridzin, in particular, was highly inhibitory to fraction B, whereas fraction A was inhibited only slightly. The phenolics in the leaves of D. falcata were highly inhibitory to both forms of enzyme.

Carbohydrate metabolism in Cuscuta

Abstract There are significant variations in the activities of enzymes of carbohydrate metabolism along the filaments of the parasite Cuscuta reflexa Roxb. Functionally, the filament is broadly separable with respect to the host into a proximal region and a distal region. The proximal region has an enzyme make-up preferentially directed to the elaboration of starch; the distal region is more suited for the catabolism of carbohydrate. The filament curled about the host contains a higher proportion of tissue protein in mitochondria and a higher oxidative and energy-trapping ability, in comparison with the apical region of filament.

Biochemical aspects of the developing and ripening banana

Abstract 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.

Effect of root parasitism by orobanche on the respiration and chlorophyll content of Petunia

Abstract Infection of Petunia by broom rape caused an increase in the respiratory rate of roots but not leaves of the host plant. There was a drop in both the chlorophyll and nitrogen levels of the leaves of infected plants.

Phosphorus, nitrogen and carbohydrate composition of the seeds of Cuscuta

Abstract The seeds of Cuscuta campestris were analysed for phosphorus, nitrogen and carbohydrate components. The seeds apparently contained sufficient reserve nutrients to initiate germination under appropriate environmental conditions and to sustain the early phase of the non-parasitic existence of seedlings. There was no tendency to accumulate phosphorus and nitrogen, but starch and polyfructosan occurred in high amounts. Phytic acid and acid-insoluble polyphosphate constituted the reserve forms of phosphorus. A distinctive feature appeared to be a relatively high concentration of phospholipids. The occurrence of significant quantities of nucleotides and the abundance of hexoses and of the dicarboxylic amino acids in the parasite seed suggested a ready potential of metabolic activity.

Nuclease activity in tissues of angiosperm parasites

Abstract The tissues of angiosperm parasites possess powerful riboniclease and deoxyribonuclease activities. The general properties of the enzymes, as studied in homogenates, resembled those of plant tissues in general. However, RNase of Cuscuta species differed from that of Orobanche cernua in that the latter was inhibited by Ca 2+ and Mg 2+ and stimulated by EDTA while the former was mostly unaffected. There were significant changes in enzymic activity in different regions of the filament of Cuscuta reflexa ; the changes were suggestive of an essentially degradative role for the enzymes.

ON CATALASE ACTIVITY IN SPORES OF ASPERGILLUS NIGER.

Summary1.A study has been made of the catalase activity of the spores of Aspergillus niger, NRRL 599. The enzyme occurs in 2 forms in the spores: (a) readily accessible, as evidenced by the activity of untreated whole spores and (b) difficultly accessible, as represented by that component which becomes fully reactive when the spores are disrupted or reactive to varying degrees on treatment with dioxane or one of the surface active agents, deoxycholate, digitonin and triton X-100. The latter form constitutes over twice the former. Barring dioxane treatment, conventional techniques failed to solubilize the enzyme.2.The two forms of catalase differ in some properties, the most important of which is the behaviour on heating for 5 min at 70°C. The accessible form undergoes inactivation to a considerable extent, whereas the inaccessible form is not significantly affected. The heat sensitive part of catalase tends to be associated with particles sedimenting from aqueous homogenates at the lowest relative centrifugal forces. The accessible form is also preferentially sensitive to storage at room temperature or in a Deep-freeze. A part of the accessible form is soluble in dioxane; the rest is insoluble. However, no distinction between the two forms was demonstrable on the basis of pH-activity relationship or inhibition by cyanide and fluoride.3.These properties could be largely accounted for by assuming that the greater part of catalase of spores is firmly bound to structural elements in the spores such as the spore coat and that the rest is east is easily accessible by occurring at the openings on this structure.

Purification and properties of cis-aconitic decarboxylase

SummaryLyophilized and stored in a deep-freeze, the mycelial material was found to retain cis-aconitic decarboxylase activity unimpaired at the end of 2 months. Mycelia could be stored also in the frozen condition but after squeezing hard to remove as much of adherent water as possible. Extracts with maximum cis-aconitic decarboxylase activity were obtained when the frozen or better the lyophilized mycelia of Aspergillus terreus were ground in a mortar with phosphate buffer using pyrex glass powder as abrasive. Cis-aconitic decarboxylase was purified 25-fold by fractionation with ammonium sulfate, starting from extracts of the mycelia in phosphate buffer. The purified enzyme was considerably more stable than the crude extracts to storage and dialysis. The optimum pH was 5.8 using 0.2 m phosphate buffer; Km value was 5×10-3m at pH 5.8 and 37°C. EDTA and 8-hydroxyquinoline activated the enzyme; all metals tested inhibited the enzyme, Zn++ and Cu++ leading to complete inactivation. Fluoride, arsenite and azide also inhibited the enzyme activity.

Studies on the germination of spores of aspergillus niger

The investigations of SgEA~ and DODGE (1927), GODDAMn (1935, 1939) and GODDARD and SMITH (1938) established that heat treatment of the ascospores of Neurospora resulted in activation. There was a large increase in respiration (GODDARD 1935), and latent carboxylase was believed to be activated (GODDARD and S~IT~ 1938). Apart from heat treatment, GODDARD (1938) showed that acetaldehyde and ethanol were able to induce a large increase in QO 2 of dormant spores of Neurospora, but that this increase was of short duration and these substances did not help in germination. The activation of Neurospora spores can also be brought about by certain other chemicals, such as furfural (EMERSON 1948; :u FJORD and CAMPBELL 1951; SUSS~ACV 1954) and some of its heterocyclic derivatives (Suss~AN 1953). TE~UI and Moc~IzvKI (1955) have shown that glucose and phosphate promote respiration in spores of Aspergillus oryzae. YANAGITA (1957) made a detailed study of certain biochemical aspects of the germination of the conidiospores of A. niger. The spores failed to germinate in water, but germinated completely in the presence of glucose, phosphate and Lalanine, without the formation of mycelium. The germination was shown to occur in three phases--endogenous swelling, exogenous swelling, and sprouting. HALESGVT~ and RUDOLP~ (1959) have shown that the sporangiospores of Phycomyces blakesleeanus can be heat-activated, leading to increased respiratory activity. The activated spores can be inactivated and reactivated.

Isoenzymicity in mouse liver guanine deaminase demonstrable under substrate stress.

Abstract Two isoenzymes of guanine deaminase could be demonstrated in the liver of mice subjected to guanine stress while the salinetreated controls showed only one. The one appearing under stress was a regulatory protein showing a sigmoidal substrate saturation curve, but was not influenced by GTP, allantoin or Mg 2+