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S Sanchez

Publications and source records attributed to S Sanchez.

At least 91 records · Page 5Linked to original sources
PubMed1986

Simultaneous bilateral testicular tumors, one side clinically occult: detection by ultrasonography.

The majority of bilateral testicular tumors are discovered sequentially. Some of these second tumors may be present subclinically at the time the initial contralateral tumor is diagnosed and their simultaneous detection with ultrasound screening would obviate the inherent problems of an otherwise sequential bilaterality. We report a case of simultaneous bilateral seminomas in which 1 of the 2 tumors was subclinical and detected with ultrasound. The various problems encountered with these asynchronous second tumors in contrast to those diagnosed simultaneously are discussed.

Adult↗
PubMed1982

Transient repression of erythromycin formation in Streptomyces erythraeus.

The effect of a D-glucose on growth and erythromycin production by Streptomyces erythraeus was investigated. D-Glucose stimulated growth and caused a strong but temporary suppression of antibiotic formation. Maximum specific suppression of erythromycin formation occurred at a carbohydrate concentration of 20 mg ml-1. A non-metabolizable analogue of glucose, 2-deoxy-D-glucose, also suppressed antibiotic formation. Since glucose caused a decrease in erythromycin formation only when added before the stage of antibiotic production, we conclude that this sugar exerted a transient repressive effect on erythromycin biosynthesis.

Deoxyglucose↗
PubMed1980

Characterization of a site-specific restriction endonuclease SphI from Streptomyces phaeochromogenes.

A new type-II restriction endonuclease SphI, has been partially purified from Streptomyces phaeochromogenes. SphI recognizes the hexanucleotide sequence 5'-GCATGC and cleaves it at the position marked by the arrow. This nucleotide sequence is present twice in SV40 DNA, four times lambda DNA and only once in the cloning vehicles pBR322, pBR325, pBR327 and pBR328.

Chromatography, DEAE-Cellulose↗
PubMed1978

Selective enrichment of aromatic amino acid auxotrophs in Hansenula polymorpha.

Aromatic amino acid auxotrophs of the methanol-utilizing yeast Hansenula polymorpha were effectively selected by the use of nystatin and a medium that inhibits the growth of tyrosine auxotrophs. The procedure resulted in a frequency of aromatic auxotrophs of 2% of survivors and an enrichment of 20-fold. The new procedure also takes less time than traditional procedures. Of the auxotrophic mutants isolated, two-thirds required tyrosine and the remainder were tyrosine-phenylalanine double auxotrophs.

Ascomycota↗
PubMed1978

Tryptophan excretion by a bradytroph of Hansenula polymorpha growing in methanol.

The growth of a bradytrophic mutant isolated from the methanol-utilizing yeast Hansenula polymorpha was found to be stimulated by both tyrosine and phenylalanine. The mutant contained about half as much chorismate mutase activity as the wild-type strain. When grown in a medium containing 2% mehtanol as the major carbon and energy source, the bradytroph excreted a low but significant level (28 mg/liter) of L-tryptophan.

Ascomycota↗
PubMed1975

Properties of D-xylose isomerase from Streptomyces albus.

A partially purified D-xylose isomerase has been isolated from cells of Streptomyces albus NRRL 5778 and some of its properties have been determined. D-Glucose, D-xylose, D-ribose, L-arabinose, and L-rhamnose served as substrates for the enzyme with respective Km values of 86, 93, 350, 153, and 312 mM and Vmax values measuring 1.23, 2.9, 2.63, 0.153, and 0.048 mumol min per mg of protein. The hexose D-allose was also isomerized. The enzyme was strongly activated by 1.0 mM Mg2+ but only partially activated by 1.0 mM Co2+. The respective Km values for Mg2+ and Co2+ were 0.3 and 0.003 mM. Mg2+ and Co2+ appear to have separate binding sites on the isomerase. These cations also protect the enzyme from thermal denaturation and from D-sorbitol inhibition. The optimum temperature for ketose formation was 70 to 80 C at pH values ranging from 7 to 9. D-Sorbitol acts as a competitive inhibitor with a Ki of 5.5 mM against D-glucose, D-xylose, and D-ribose. Induction experiments, Mg2+ activation, and D-sorbitol inhibition indicated that a single enzyme (D-xylose isomerase) was responsible for the isomerization of the pentoses, methyl pentose, and glucose.

Arabinose↗
PubMed1975

D-Glucose isomerase: constitutive and catabolite repression-resistant mutants of Streptomyces phaeochromogenes.

As in other Streptomyces species, the enzymatic conversion of D-glucose to D-fructose is carried out in Streptomyces phaeochromogenes NRRL B-3559 by the inducible enzyme, D-xylose keto isomerase (EC 5.3.1.5). Mutants of this microorganism were selected for their ability to grow on D-lyxose (2-epimer of D-xlose). As a result of the mutational event, the microorganism constitutively produced D-xylose isomerase. As in the parent strain, the constitutive formation of the isomerase was repressed by D-glucose. The fact that this mutant was unable to grow in low D-xylose concentrations in the presence of the D-glucose analogue, 3-O-methylglucose, permitted the isolation of D-xylose isomerase constitutive mutants which were insensitive to D-glucose repression.

Carbohydrate Epimerases↗
PubMed1972

Regulation of arginase activity by intermediates of the arginine biosynthetic pathway in Neurospora crassa.

It has been found that, in Neurospora crassa, arginine synthesized from exogenous citrulline was not as effectively hydrolyzed as exogenous arginine. This was explained by the observed inhibition of arginase in vitro and in vivo by citrulline. The high arginine pool formed from exogenous citrulline feedback inhibits the arginine pathway. These two factors allow exogenous citrulline to be used adventitiously and efficiently as an arginine source. Finally, it was found that ornithine was a strong inhibitor of arginase. This suggests that the characteristically high ornithine pool of minimal cultures of Neurospora may act to control a potentially wasteful catabolism of endogenous arginine by arginase.

Arginase↗
PubMed1972

Interactions between amino acid transport systems in Neurospora crassa.

Mutants of Neurospora crassa, selected as resistant to l-canavanine and l-thialysine, are partially deficient in the uptake of basic amino acids. Neutral amino acids completely inhibit uptake of basic amino acids, and this inhibition is dependent on the activity of a neutral amino acid permease. In contradistinction, mutants resistant to 4-methyl-dl-tryptophan are partially deficient in the uptake of neutral amino acids. Basic amino acids completely inhibit neutral amino acid uptake, and this inhibition is dependent on the activity of a basic amino acid permease. It is proposed that these specific transport systems compete with a general amino acid permease for some common element. The general permease is also regulated by ammonia, the amino acid pool, or both. The activity of the general permease can be eliminated phenotypically by a high concentration of glycerol or a high temperature. It is also shown that l-citrulline is transported by the neutral amino acid permease and by the general amino acid permease.

Amino Acids↗