SynopsisThe conformation of (3-casein A in the monomeric and thermally aggregated states has been investigated by a range of techniques. P-Casein exists as a monomer in solution a t 4°C and a t concentrations up to a t least 3 g/dl. The molecule is flexible and exhibits a lot of segmental motion, but its secondary structure is not wholly random coil; about one-third of the polypeptide chain is ordered and the likely locations of these regions are discussed. The radius of gyration, representing the time-average distribution of the flexible chain, is 46 A. Increasing temperature leads to aggregation of the P-casein molecules. The degree of association is very sensitive to experimental conditions, and under our conditions a 14-mer exists a t 20°C. The aggregate is spherical with a radius of about 100 A. The interior of the aggregate is relatively disordered, and the P-casein molecules remain in a largely flexible, hydrated conformation. The volume restriction of the protein molecules which occurs on association leads tvsome immobilization of the hydrophobic C-terminal region, which is packed toward the center of the aggregate.

SummaryThe problem of fruit size in the Australian apple variety Granny Smith was examined in relation to mean cell size and mean cell number. Cell size gradients in the fruit and changes in cell shape and packing during development were noted.Observations of workers on other varieties that cell division ceased within four weeks of pollination were confirmed. Variation in size of fruits at maturity was shown to be due mostly to variation in cell number and only to a small extent to mean cell size. Cell enlargement was shown to continue throughout the life of the fruits on the tree.

Summary 2,4-Dinitrophenol, while increasing the respiration, inhibits the accumulation of ions by carrot cells. Further investigation is necessary to determine whether the inhibition is due to a direct effect of the dinitrophenol on the mechanism or whether the dinitrophenol indirectly prevents the mechanism from operating by causing some disorganization within the cell, possibly in the mitochondria. If the assumption that dinitrophenol inhibits phosphate transfers is justifiable, hypotheses of salt accumulation might require modification to allow for the participation of energy-rich phosphate. This would suggest that the Lundegardh mechanism may be a part of a more complex mechanism.

Deuteriated analogues of ubiquinone 10 (Q10) have been dispersed with plasma membranes of Escherichia coli and with the inner membranes of beetroot mitochondria. Orientational order at various deuteriated sites was measured by solid-state deuterium nuclear magnetic resonance (2H NMR). Similar measurements were made, using the compounds dispersed in dimyristoylphosphatidylcholine (DMPC) and egg yolk lecithin and dispersions prepared from the lipid extracts of beetroot mitochondria. In all cases only a single unresolved 2H NMR spectrum (typically 1000-Hz full width at half-height) was observed at concentrations down to 0.02 mol % Q10 per membrane lipid. This result shows that most Q10 is in a mobile environment which is physically separate from the orientational constraints of the bilayer lipid chains. In contrast, a short-chain analogue of Q10, in which the 10 isoprene groups have been replaced by a perdeuteriated tridecyl chain, showed 2H NMR spectra with quadrupolar splittings typical of an ordered lipid that is intercalated into the bilayer. The NADH oxidase activity and O2 uptake in Escherichia coli and in mitochondria were independent of which analogue was incorporated into the membrane. Thus, despite the major difference in their physical association with membranes, or their lipid extracts, the electron transport function of the long- and short-chain ubiquinones is similar, suggesting that the bulk of the long-chain ubiquinone does not have a direct function in electron transporting activity. The physiologically active Q10 may only be a small fraction of the total ubiquinone, a fraction that is below the level of detection of the present NMR equipment.(ABSTRACT TRUNCATED AT 250 WORDS)

Pea fruits from two crops were sampled at different times from flowering. Changes in the fresh weight, dry weight, starch, soluble carbohydrate, protein nitrogen, and soluble nitrogen in both seeds and hulls were followed in two seasons and related Jo the changes in cell volume in the seeds. In one season respiration rates and phosphate, pectin, and ascorbic acid contents were also investigated. The seeds gained more carbohydrate and nitrogen than was lost by the hulls. Starch and protein were synthesized rapidly by the seeds. The increase in starch content in the seeds was followed by a decrease in soluble carbohydrate content, after which the seed ceased to accumulate water. These metabolic changes are discussed in the light of recent biochemical knowledge, and in relation to more detailed biochemical investigations in progress.