An electron microscopic study on the mating tube formation in the heterobasidiomycete Tremella mesenterica

Ultrastructure of the mating tube formed in yeast haplont of the heterobasidiomycete Tremella mesenterica was studied by electron microscopy. Cell wall of the mating tube emerged as evagination of the inner layers, rupturing outer layers of the mother cell wall. Comparison with budding cells suggested that the tube emergence place at bud scar and the process of tube emergence was the same as that of bud emergence. Electron transparent vesicles of 0.1 m diameter were scattered in the cytoplasm of the mating tube. Nucleus-associated organelle was located at one side of the nuclear envelope which extended towards the mating tube. A few microtubules were detected in the mating tube, but their association with a nucleus was not clear. The cytoplasmic structure of the mating tube was discussed in comparison with that of hyphae of the filamentous fungi.     

Bitter Taste of Synthetic C-Terminal Tetradecapeptide of Bovine β-Casein,H-Pro196-Val-Leu-Gly-Pro-Val-Arg-Gly-Pro-Phe-Pro-Ile-Ile-Val209-OH,and Its Related Peptides

The primary structure of bovine β-casein contains the partial sequence of -Pro¹⁹⁶-Val-Leu-Gly-Pro-Val-Arg-Gly-Pro-Phe-Pro-Ile-Ile-Val²⁰⁹ in the C-terminal portion. We previously reported that the synthetic C-terminal octapeptide, Arg²⁰²-Val²⁰⁹, is extremely bitter with its threshold value 0.004 mm, 250 times as strong as that of caffeine. To further investigate the bitter taste of the C-terminal portion of β-casein, we synthesized the C-terminal tetradecapeptide, Pro¹⁹⁶-Val²⁰⁹, and some of its fragments. A hydrophobic hexapeptide, Pro¹⁹⁶-Val²⁰¹, was twice as bitter as caffeine. The bitter taste of the decapeptide, Pro²⁰⁰-Val²⁰⁹, was the same as that of Arg²⁰²-Val²⁰⁹. Although the tetradecapeptide, Pro¹⁹⁶-Val²⁰⁹, was composed of two bitter peptides, Pro¹⁹⁶-Val²⁰¹ and Arg²⁰²-Val²⁰⁹, its bitter taste was weaker than that of Arg²⁰²-Val²⁰⁹ and its threshold value was 0.015 mm. We suggested that the increase of bitterness in peptides through the introduction of hydrophobic amino acids depended on the number of hydrophobic amino acids added. In addition, the synthetic retro analog of Arg²⁰²-Val²⁰⁹ (H-Val-Ile-Ile-Pro-Phe-Pro-Gly-Arg-OH) was not as bitter as Arg²⁰²-Val²⁰⁹. This indicated that the sequence of Arg²⁰²-Val²⁰⁹ is important for extreme bitterness.     

Interaction of apolipoprotein B-containing lipoprotein secreted by Hep G2 cells with receptors for low-density lipoprotein.

Radioligand and immunoenzymatic techniques were used to characterize the receptor binding properties of apolipoprotein B-containing lipoprotein produced by HepG2 cell line (H-LpB). It was found that compared to plasma low-density lipoprotein (LDL), the interaction of H-LpB nonseparated from conditioned medium with normal fibroblasts was 6-8-times lower and only slightly exceeded the nonspecific binding of LDL modified by malondialdehyde, while the uptake of the indicated lipoproteins by LDL receptor-negative strain of fibroblasts were identical. The uptake of H-LpB by normal fibroblasts increased 1.5-2-times after isolation from the culture medium by immunoaffinity chromatography. The effect of isolation could be explained by the finding that apolipoprotein E-containing lipoprotein secreted by HepG2 cells effectively competed for the binding with LDL-receptors. The obtained results suggest that H-LpB produced by HepG2 cells is poorly recognized by the LDL-receptors.     

Biochemical Conversion of Uridine Diphosphate Glucose to Uridine Diphosphate 3-Ketoglucose by Washing Cells of Agrobacterium tumefaciens

The relation between the rate of increase in nonprotein nitrogenous compounds (NPN) of rabbit muscle and muscle pH ranging from 5.9 to 7.2 was examined during the post-mortem storage. Muscle of a high ultimate pH was prepared by the injection of ICH₂COOH into the vein. The more the muscle pH kept away from 6.3, the more NPN increased. Therefore, it has been suggested that the post-mortem proteolysis is mainly attributed to the acid proteolytic system comprising cathepsins in muscles at a pH lower than 6.3 and to the neutral proteolytic system in muscles at a pH higher than 6.3.

The ratio of the increment of ninhydrin positive materials to that of Cu-Folin phenol reagent positive materials among NPN was relatively large in muscles at a high pH. This result has suggested that the neutral proteolytic system was more abound in exopeptidase activity than acid proteolytic system.     

Subunit Structure of Glucoamylase of Saccharomyces diastaticus

Extracellular glucoamylase produced by a starch-fermenting yeast, Saccharomyces diastaticus 5106-9A, was purified. The enzyme was found to be heterogeneous in molecular weight, ranging from approximately 80K to 66K as estimated by gel filtration, and consisted of two subunits, H and Y. The molecular weight of subunit H was heterogeneous and was determined to be approximately 68K, 59K, and 53K by acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The molecular weight of subunit Y was 14K, estimated by the same gel. the molecular weight of the deglycosylated form of subunit H was 41K, suggesting that the heterogeneity of the enzyme was due to glycosyl moieties of subunit H. Subunits H and Y were separated by gel filtration in the presence of sodium dodecyl sulfate. Subunit Y seemed to be hydrophobic, since it was insoluble in an aqueous buffer without detergent.