Surface study of apoB1694�C1880, a sequence that can anchor apoB to lipoproteins and make it nonexchangeable

Apolipoprotein B (apoB) is a nonexchangeable apolipoprotein. During lipoprotein assembly, it recruits phospholipids and triacylglycerols (TAG) into TAG-rich lipoprotein particles. It remains bound to secreted lipoproteins during lipid metabolism in plasma. The β1 region (residues 827–1880) of apoB has a high amphipathic β strand (AβS) content and is proposed to be one region anchoring apoB to lipoproteins. The AβS-rich region between apoB37 and apoB41 (residues 1694–1880) was cloned, expressed, and purified. The interfacial properties were studied at the triolein/water (TO/W) and air/water (A/W) interfaces. ApoB[37–41] is surface-active and adsorbs to the TO/W interface. After adsorption the unbound apoB[37–41] was removed from the aqueous phase. Adsorbed apoB[37–41] did not desorb and could not be forced off by increasing the surface pressure up to 23 mN/m. ApoB[37–41] adsorbed on the TO/W interface was completely elastic when compressed and expanded by ±13% of its area. On an A/W interface, the apoB[37–41] monolayer became solid when compressed to 4 mN/m pressure indicating extended β-sheet formation. It could be reversibly compressed and expanded between low pressure and its collapse pressure (35 mN/m). Our studies confirm that the AβS structure of apoB[37–41] is a lipid-binding motif that can irreversibly anchor apoB to lipoproteins.     

The effect of relative humidity on the shape ofBacillus apiarius spores

Bacillus apiarius spores have been examined at relative humidities between 99% and 12% in a scanning electron microscope modified to enable wet specimens to be studied. The spores have also been studied both wet and dry with an interference microscope. Their shape remains rectangular whether wet or dry. A calculation of the effect of an osmotic pressure change of about 200 atm upon the maximum deflection of the longest side of the spore shows that the deflection is less than 4.5 nm. The shape of the spore therefore is not markedly affected by a change from dry to wet and the shape will remain as it was when the coat was initially formed, unless the coat is weakened by some chemical attack. The refractive index of the coat material is 1.532–1.536.     

RIBOFLAVIN AND MOUSE HEPATIC CELL STRUCTURE AND FUNCTION : II. Division of Mitochondria during Recovery from Simple Deficiency

Mice which had been on a riboflavin-free diet for 6–8 wk were given daily intraperitoneal injections of riboflavin. The hepatic mitochondria, which in the deficient animals were greatly enlarged, were restored to normal dimensions within 3 days. Normalization of the mitochondrial population was brought about by division of the giant organelles. Dividing mitochondria were characterized by a membranous partition separating the inner compartment into two distinct chambers. Such organelles showed varying degrees of pinching at the level of the partition. The most common site of partition formation was at the base of a small mitochondrial bud. During the 1st day of recovery, dividing mitochondria were so common that they could be easily found in mitochondrial pellets. Injection of riboflavin into normally nourished mice also produced an apparent increase in the frequency of dividing mitochondria in the liver cells.