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Y K Oh

Publications and source records attributed to Y K Oh.

At least 55 records · Page 3Linked to original sources
PubMed1986

Glycopeptide antibiotics: a mechanism-based screen employing a bacterial cell wall receptor mimetic.

The evolution of a highly targeted screening program for the discovery of antibiotics of the glycopeptide (vancomycin) class is described. A holistic approach was utilized which optimized not just screening techniques but also the selection of candidate producer cultures and their growth under conditions which enhanced production of target compounds. Two screen techniques were utilized; differential inhibition of a vancomycin-resistant strain and its susceptible parent, and a specific antagonism screen using the reversal of glycopeptide activity by a tripeptide analog of the glycopeptide receptor, diacetyl-L-lysyl-D-alanyl-D-alanine. The latter screen was 2- to 32-fold more sensitive to known glycopeptides than the former, and was absolutely specific, yielding no false positive responses. The use of the tripeptide antagonism assay, combined with optimized culture selection and growth conditions yielded novel glycopeptide antibiotics at a rate of 1 per 320 cultures screened. With a holistic approach to screening and properly optimized techniques, large numbers of cultures do not need to be examined in order to discover novel antibiotics.

Actinomycetales↗
PubMed1986

Biosynthetic studies of aridicin antibiotics. I. Labeling patterns and overall pathways.

Biosynthetic feeding experiments with 14C and 13C-labeled precursors in Kibdelosporangium aridum have established the biosynthetic origins of the heptapeptide aglycone of the aridicin antibiotics, and the tentative sequence of the later stage biosynthetic transformations. The aglycone moiety has been found to be derived from tyrosine, sodium acetate and L-methionine. It is suggested that the preformed aglycone is first mannosylated and then followed by the attachment of the glycolipid. The sugar oxidation to the glucuronic acid level was found to take place as a terminal step of the biosynthesis.

Acetates↗
PubMed1986

Biosynthetic studies of aridicin antibiotics. II. Microbial transformations and glycosylations by protoplasts.

In connection with the biosynthetic studies of the aridicin antibiotics in Kibdelosporangium aridum, various microorganisms, known to produce related glycopeptide antibiotics, have been examined for their glycosylating activity. A number of strains were found to mannosylate the aridicin aglycone, while Actinoplanes teichomyceticus was found to have deacylating activity as well. A protoplast system of K. aridum was developed and was found to possess novel glycosylating activity in addition to the mannosylating activity which was also present in the whole cells. Effects on the glycosylating activity by various membrane solubilizing agents have been discussed.

Actinomycetales↗
PubMed1986

A cryptic plasmid from Nocardia orientalis NRRL 2452, a vancomycin producer.

A plasmid was found in Nocardia orientalis (formerly Streptomyces orientalis). Physical characterization of the plasmid DNA indicates a size of 33.5 kb and a single cleavage site for EcoR I. The presence of plasmid, and variation in its copy member, did not directly affect vancomycin resistance or production levels. The plasmid represents the first to be isolated and characterized from a glycopeptide-producing nocardia.

Chromosome Mapping↗
PubMed1985

Prolonged survival of the Graafian follicle and fertilization in the Japanese greater horseshoe bat, Rhinolophus ferrumequinum nippon.

After the mating season of the Japanese greater horseshoe bat in mid- or late October, only the right ovary maintained a single Graafian follicle throughout hibernation until early April. During this time the ovum was in prophase of meiosis I (resting stage) with many large lipid droplets as a nutrient source. In synchrony with stigma formation, there was resumption of meiotic activity, separation of the cumulus oophorus from the granulosa layer and dispersion of the follicle cells just before ovulation in spring. The block to polyspermy seemed to reside in the zona pellucida, because no spermatozoa could be detected in the perivitelline space of the 6 fertilized ova examined, although a second spermatozoon was recognized in the zona pellucida of 3 ova.

Animals↗
PubMed1984

Sperm invasion of the oviducal mucosa, fibroblastic phagocytosis and endometrial sloughing in the Japanese greater horseshoe bat, Rhinolophus ferrumequinum nippon.

In the Japanese greater horseshoe bat, Rhinolophus ferrumequinum nippon, a vast number of spermatozoa invade the oviducal epithelial cells of the caudal isthmus and become concentrated in the endometrial lamina propria of the bicornuate horns. They are subsequently phagocytised and digested by fibroblasts. Then, finally, they become deposited in the uterine lumen together with a large quantity of secretory material from the endometrial connective tissue which, prior to this event, undergoes a massive infiltration by polymorphonuclear leucocytes.

Animals↗
PubMed1983

Studies on the vaginal plug of the Japanese greater horseshoe bat, Rhinolophus ferrumequinum nippon.

The vaginal plug of the Japanese greater horseshoe bat is composed of an outer, thick, hard and homogeneous layer originating from the stratum disjunctum of the vaginal mucosa and a thin, soft and opaque central core containing accidentally trapped dead spermatozoa. The vaginal plug appeared to be expelled just before or after ovulation in spring. Immediately after copulation in autumn, uterine spermatozoa were dead but few leucocytes were present. As time passes after copulation, however, the infiltration of leucocytes into the uterus increased gradually, and extensive leucocytic phagocytosis of dead spermatozoa occurred during hibernation.

Animals↗
PubMed1981

Influence of pH on spore aggregation of Streptosporangium brasiliense.

Spores of Streptosporangium brasiliense aggregated at acidic pH's and were dissociated into free spores by changing to neutral or alkaline pH's. This finding was utilized in preparing uniform spore suspension, in which simple filtrations gave rise to consistent preparation of free spores at alkaline pH.

Actinomycetales↗
PubMed1978

In vitro fertilizing ability of testicular, epididymal, and ejaculated rabbit spermatozoa.

The fertilizing ability of testicular, epididymal, and ejaculated rabbit spermatozoa was evaluated in vitro following in vitro capacitation by high ionic strength treatment. Fewer than 11% of inseminated ova were apparently fertilized (i.e., in pronuclear, two-, and four-cell stages as determined by light microscopy) when testicular sperm treated with caffeine, caput epididymal, or corpus epididymal sperm samples were tested. A greater fertilizing ability, reflected by the percentage of ova fertilized and more normal progression of embryonic development, was exhibited by cauda epididymal sperm. Of 93 ova, 68 (73.1%) were fertilized by cauda sperm, whereas ejaculated sperm from the same 10 bucks fertilized 34 (36.6%) of 93 ova (P is less than 0.005). Ultrastructural examination of selected ova apparently fertilized by sperm from levels of the male reproductive tract proximal to the cauda epididymidis revealed abnormal activation. Authentic fertilization occurred when ova were inseminated with cauda epididymal and ejaculated sperm. An unusual and infrequent form of activation involving failure of cortical granule breakdown in ova penetrated by cauda epididymal and ejaculated sperm was seen. A comparison of fertilizing ability of sperm from first, second, and third ejaculates revealed a significant decrease with the third ejaculate (P is less than 0.01).

Animals↗
PubMed1976

Manganese requirement of phosphoglycerate phosphomutase and its consequences for growth and sporulation of Bacillus subtilis.

In the absence of manganese, rapidly metabolizable carbohydrates such as glucose or glycerol are not completely metabolized by Bacillus subtilis growing in a nutrient sporulation medium: 3-phosphoglyceric acid (3PGA) accumulates inside the cells, growth stops at a low cell titer, and normal sporulation remains suppressed (no prespore septa). Upon the addition of manganese, 3PGA disappears, growth resumes, and normal sporulation takes place. These effects results from a specific manganese requirement of phosphoglycerate phosphomutase which catalyzes the interconversion of 3PGA and 2-phosphoglyceric acid (2PGA). Other metal ions cannot replace manganese, for which the enzyme has an apparent Km of 0.22 mM.

Bacillus subtilis↗
PubMed1975

Ultrastructure of rabbit ova recovered from ovarian follicles and inseminated in vitro.

Rabbit ova were obtained from presumably preovulatory ovarian follicles of gonadotropin-treated does and inseminated with uterine sperm in vitro. Ova were serially sectioned for light and electron microscopy 0, 1 1/2, 3, 6, and 9 hours after in vitro insemination. Control ova were maintained in culture for 25 hours and examined by light microscopy for cleavage. Little difference in fertilization rate (i.e., ova fertilized/ova inseminated) was observed when criteria were based on ultrastructural evidence (56.5%) and on light microscopic evidence 25 hours post-insemination provided by cleavage of control ova (54.8%). Therefore, observations of cleavage (as in controls here) can be an accurate criterion for fertilization in the rabbit, at least under the in vitro conditions used in this study. After insemination of ova recovered from preovulatory follicles, the developmental sequence was as follows: after 1 1/2 hours, sperm penetration into the vitellus; after 3 hours, male pronuclear formation and second polar body extrusion; after 6 hours, male and female pronuclear enlargement; and after 9 hours, pronuclei in apposition. This sequence compares favorably with the normal temporal sequence of events already well known for fertilization of ovulated ova in the rabbit. Penetrating sperm cells within the matrix of the zona pellucida and the supplementary sperm cells lying in the perivitelline space had undergone the acrosome reaction. Changes associated with the acrosome reaction took place before the penetration of the zona pellucida. The presence of a number of supplementary sperm, usually five to six per ovum, within the perivitelline space of the already activated ovum indicated that the block to polyspermy in these experiments operated mainly at the level of the vitelline membrane, as is the case in the normal fertilization process. The vitelline membrane block to polyspermy occurred rapidly after penetration of the fertilizing sperm into the vitellus and was associated with cortical granule breakdown. Ultrastructural details of rabbit ova recovered from ovarian follicles and inseminated in vitro revealed no distinguishable characteristics when compared with reported observations of ovulated rabbit ova undergoing fertilization in vivo.

Acrosome↗
PubMed1974

Adenosine 5'-triphosphate release and membrane collapse in glycerol-requiring mutants of Bacillus subtilis.

Glycerol-requiring mutants of Bacillus subtilis could not sporulate in nutrient sporulation medium even when additional glycerol was added from the beginning of growth. Sporulation could be partially restored either by the frequent addition of small amounts of glycerol during the developmental period or by the single addition of both 10 mM glycerol and 10 mM malate. But sporulation could be completely restored by the addition of 50 mM glycerol-phosphate from the beginning. At the end of growth of the glycerol mutants in nutrient sporulation medium, the cell membrane collapsed and separated from the cell wall, and much of the cellular adenosine 5'-triphosphate was released into the medium. These observations were made in two glycerol mutants, one derived from strain 168 containing glycerol-teichoic acid in the cell wall and the other derived from strain W23 containing ribitol-teichoic acid.

Adenosine Triphosphate↗