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L S Herrera

Publications and source records attributed to L S Herrera.

10 recordsLinked to original sources
PubMed1996

Invertase secretion in Hansenula polymorpha under the AOX1 promoter from Pichia pastoris.

A DNA fragment containing a transcription regulating region of the alcohol oxidase (AOX1) gene from the methylotrophic yeast Pichia pastoris was used in the construction of a vector for the expression of heterologous proteins in the methylotrophic yeast Hansenula polymorpha. We used this vector to clone the SUC2 gene from Saccharomyces cerevisiae into H. polymorpha yeast. The culture conditions for invertase production using a fed-batch culture were studied. More than 1.5 x 10(3) U/ml of biologically active invertase (1 g/l) were secreted to the cellular periplasmic space. The fermentative process was scaled up to 50 l. Invertase produced from H. polymorpha was glycosylated, but it contained significantly less carbohydrate than protein produced by S. cerevisiae. Using the Western-blot technique, it was observed that invertase secreted from H. polymorpha and invertase secreted from S. cerevisiae showed common antigenic determinants.

Alcohol Oxidoreductases↗
PubMed1983

Aspartate kinase and homoserine dehydrogenase of Candida utilis.

Aspartate kinase and homoserine dehydrogenase activity were assayed in a dialyzed cell-free extract of Candida utilis. Aspartate kinase was partly inhibited by ATP-Mg and by Mg2+ alone. There appear to be two isoenzymes of aspartate kinase in the yeast, one heat-labile, the other relatively heat-stable. The first is subject to feedback inhibition by threonine, the other is threonine-resistant. Neither aspartate kinase nor homoserine dehydrogenase is the rate-limiting enzyme in methionine biosynthesis. Homoserine dehydrogenase measured in the forward direction showed an activity five times higher than aspartate kinase. No regulatory interaction could be demonstrated for this enzyme. No repression of aspartate kinase and homoserine dehydrogenase synthesis by threonine, methionine or both amino acids was observed.

Adenosine Triphosphate↗
PubMed1982

Coordinate regulation of the pentose phosphate pathway and of the activity of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase (decarboxylating).

The activities of glucose-6-phosphate dehydrogenase (GPD) and 6-phosphogluconate dehydrogenase (decarboxylating) (PGD) in Saccharomyces cerevisiae were found to change by a factor similar to the reported changes in the rate of the pentose phosphate pathway between cells grown in minimal medium and in rich medium. It is suggested that the rate of this pathway is regulated not only by the activity of GPD, a well-known key enzyme, but also by PGD. These two enzymes seem to function in a coordinated fashion.

Amino Acids↗
PubMed1981

A simple procedure to obtain yeast hexokinase free of glucosephosphate isomerase and mannosephosphate isomerase.

A hexokinase preparation was obtained from a Saccharomyces cerevisiae mutant strain deficient in glucosephosphate isomerase (GPI) and mannosephosphate isomerase (MPI) by precipitation with ammonium sulfate. The supernatant fraction corresponding to 40-60 % saturation showed the lowest content in GPI and MPI activity. The fraction was used without further purification in the determination of glucose, either free or in a mixture with fructose and mannose. The results were similar to those obtained with pure commercial hexokinase.

Ammonium Sulfate↗
PubMed1981

Methionine-defective mutants in Candida utilis.

Ethionine-resistant mutants of Candida utilis CCY-158 overproducing methionine have been isolated. In these mutants the intracellular methionine concentration decreased significantly during the stationary phase. The wild-type strain CCY-158 and the ethionine-resistant mutants isolated were able to use methionine as the nitrogen source but not as the carbon source. From these ethionine-resistant mutants we isolated mutants unable to use methionine as nitrogen source (Mec- mutants), the principal alteration being at the level of methionine uptake. Some of the Mec mutants lost also the ability to use other amino acids as nitrogen source.

Candida↗
PubMed1981

Protoplast fusion in the yeast Candida utilis.

Protoplasts obtained by snail enzyme treatment from two stable auxotrophic mutants of the yeast Candida utilis were induced to fuse by the use of polyethylene glycol. The hybrids formed from the auxotrophic parental strains were selected by complementation on stabilized minimal medium. Many of the hybrids were unstable and readily dissociated into their parental strains. Others, in which parental nuclei had fused, gave stable hybrid progeny. cytological and genetic evidence of these processes is presented.

Candida↗
PubMed1979

Optimization on the selection of auxotrophic mutants in Candida utilis by snail enzyme treatment.

The determination of the best conditions for the application of the snaill enzyme digestion method in the enrichment of auxotrophic mutants in Candida utilis was carried out following Box and Wilson's mathematical method. The selection procedure proposed was tested in the enrichment of auxotrophic mutants from a mutagenized culture of a wild-type strain. Mutant frequency was increased 46-fold by treatment with snail enzyme. The method also proved useful in the selection of additional auxotrophic mutations from single auxotrophs.

Amino Acids↗
PubMed1976

Genetic and biochemical studies of phosphomannose isomerase deficient mutants of Saccharomyces cerevisiae.

Three mannose-negative mutants of Saccharomyces cerevisiae have been isolated. These mutants showed growth inhibition when mannose was added to a growth medium containing glycerol or fructose. Crosses between wild type mutants showed segregation of 2+/2-. Crosses between the mutants themselves showed that they were closely linked. Two mutants (XM3 and D2) showed characteristics of allelic structural alteration of phosphomannoseisomerase. Mutant D4 had a deficiency of phosphomannoseisomerase activity, but with a normal thermostability. Revertants from D4 had a normal thermostability.

Adenine↗
PubMed1976

Use of snail enzyme for the selection of glucose-and mannose-negative mutants in Saccharomyces cerevisiae.

The relationship between growth and sensitivity of Saccharomyces cerevisiae cells to snail enzyme led us to work out the conditions for using this enzyme to isolate mannose-negative and glucose-negative mutants. The technique is based on a prior growth on a glycerol medium in which any cell becomes resistant to snail enzyme, followed by a period of growth in a medium in which only the wild-type cells can grow, thereby becoming sensitive to the enzyme. This technique was very effective in both tested cases. This result suggests that the method described might also be applied to isolate other kinds of mutant.

Ethyl Methanesulfonate↗