Carboxylation of [beta]-methylcrotonyl coenzyme A by a purified enzyme from chicken liver

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32472/1/0000557.pd

The yeast multidrug resistance pump, Pdr5p, confers reduced drug resistance in erg mutants of Saccharomyces cerevisiae

Mutants of Saccharomyces cerevisiae bearing lesions in the ergosterol biosynthetic pathway exhibit a pleiotropic drug-sensitive phenotype. This has been reported to result from an increased permeability of the membranes of the mutant strains to different drugs. As disruption of the yeast multidrug resistance protein, Pdr5p, results in a similar pleiotropic drug-sensitive phenotype, the possibility that Pdr5p may be functioning with a reduced efficiency in these altered sterol backgrounds was examined. To do this, the function of Pdr5p in isogenic strains of S. cerevisiae that have disruptions in the late stages of the ergosterol biosynthesis pathway (ERG6, ERG2, ERG3, ERG4) was studied. A reduced ability of Pdr5p to confer resistance to different drugs in these strains was observed, which did not appear to be dependent solely on the permeability of the membrane towards the drug. A simultaneous examination was made of how the lipid composition might be altering the efficiency of Pdr5p by similar studies in strains lacking phosphatidylserine synthase (encoded by CHO1). The results indicated that the drug sensitivity of the erg strains is, to a significant extent, a result of the reduced efficiency of the Pdr5p efflux pump, and that the membrane environment plays an important role in determining the drug resistance conferred by Pdr5p

A futile cycle, formed between two ATP-dependant γ-glutamyl cycle enzymes, γ-glutamyl cysteine synthetase and 5-oxoprolinase: the cause of cellular ATP depletion in nephrotic cystinosis?

Cystinosis, an inherited disease caused by a defect in the lysosomal cystine transporter (CTNS), is characterized by renal proximal tubular dysfunction. Adenosine triphosphate (ATP) depletion appears to be a key event in the pathophysiology of the disease, even though the manner in which ATP depletion occurs is still a puzzle. We present a model that explains how a futile cycle that is generated between two ATP-utilizing enzymes of the γ-glutamyl cycle leads to ATP depletion. The enzyme γ-glutamyl cysteine synthetase (γ-GCS), in the absence of cysteine, forms 5-oxoproline (instead of the normal substrate, γ-glutamyl cysteine) and the 5-oxoproline is converted into glutamate by the ATP-dependant enzyme, 5-oxoprolinase. Thus, in cysteine-limiting conditions, glutamate is cycled back into glutamate via 5-oxoproline at the cost of two ATP molecules without production of glutathione and is the cause of the decreased levels of glutathione synthesis, as well as the ATP depletion observed in these cells. The model is also compatible with the differences seen in the human patients and the mouse model of cystinosis, where renal failure is not observed

Yct1p, a novel, high-affinity, cysteine-specific transporter from the yeast Saccharomyces cerevisiae

Cysteine transport in the yeast Saccharomyces cerevisiae is mediated by at least eight different permeases, none of which are specific for cysteine. We describe a novel, high-affinity, (Km = 55 μM), cysteine-specific transporter encoded by the ORF YLL055w that was initially identified by a combined strategy of data mining, bioinformatics, and genetic analysis. Null mutants of YLL055w, but not of the other genes encoding for transporters that mediate cysteine uptake such as GAP1, GNP1, MUP1, or AGP1 in a met15Δ background, resulted in a growth defect when cysteine, at low concentrations, was provided as the sole sulfur source. Transport experiments further revealed that Yll055wp was the major contributor to cysteine transport under these conditions. The contributions of the other transporters became relevant only at higher concentrations of cysteine or when YLL055w was either deleted or repressed. YLL055w expression was repressed by organic sulfur sources and was mediated by the Met4p-dependent sulfur regulatory network. The results reveal that YLL055w encodes the principal cysteine transporter in S. cerevisiae, which we have named YCT1 (yeast cysteine transporter). Interestingly, Yct1p belongs to the Dal5p family of transporters rather than the amino acid permease family to which all the known amino acid transporters belong

Isolation and characterization of glycosaminoglycans in human brain of different age groups

Five distinct glycosaminoglycan fractions have been isolated from human brain of various age groups, by employing an improved fractionation procedure. Analysis of these fractions showed that human brain contains hyaluronic acid, chondroitin-4-sulphate, chondroitin-6-sulphate, dermatan sulphate, heparan sulphate and two unidentified low sulphated fractions. The pattern of variation of these compounds with age, indicates that they may be playing an important role in the process of myelination and brain maturation

The regional distribution, age dependent variation and species differences of brain arylsulphatases

The relative proportions of arylsulphatase A and B were determined by the method of Baum, Dodgson and Spencer (1959) in brains of various animal species and it was found that there was a considerable variation in the concentration of these two enzymes. Arylsulphatase A and B of various animal species including rat, man, monkey, sheep and chicken were partially separated using zinc acetate fractionation procedure and gel electrophoresis. The chicken brain arylsulphatase A had a similar electrophoretic mobility to that of arylsulphatase B of other species. Further, chicken brain arylsulphatase A precipitated at a zinc acetate concentration of 0005 M, a condition under which arylsulphatase B from the brain of other species precipitated. Kinetic properties such as Km value and inhibitory effect of sulphite and phosphate ions indicated that chicken brain arylsulphatase A was similar to arylsulphatase A of other species. The results on regional distribution of arylsulphatase A and B activities in monkey brain and in developing rat brain suggest a relationship between arylsulphatase A and sulphatides and arylsulphatase B and mucopolysaccharides

Liposomes in immunology

Liposomes, the artificial phospholipid vesicles, have the capacity of entrapping water soluble substances in their aqueous compartments. Of the many possible potentials of liposomes their application in immunology is most significant. Recent studies have shown an adjuvant and a carrier effect of liposomes to a number of antigens. Liposomes used in these studies are generally multilamellar vesicles with the antigen encapsulated in the aqueous phase. Some antigens may also be associated with the lipid lamellae covalently or noncovalently. The adjuvant property of liposomes is greatly affected by the surface charge of the vesicle as well as the site of association of the antigen. The other factors which may have a role in immunopotentiation by liposomes are the size and structure of the vesicles, the lipid composition, route of administration and their surface sugars. In addition, liposomes may function as carriers to haptens and other antigens. In association with liposomes the nature of the immune response may be modulated. For a further enhancement of the adjuvant activity of liposomes use has been made of immunomodulators

Enzymatic desulphation of cerebroside-3-sulphate by chicken brain arylsulphatase A

In earlier work from this laboratory it was shown that arylsulphatase of chicken brain resembles arylsulphatase A of other animal species in several of its properties but exhibits certain characteristics similar to that of arylsulphatase B (Farooqui and Bachhawat, 1971). Recently the arylsulphatase A of chicken brain was purified and it was demonstrated that the purified enzyme could desulphate cerebroside-3-sulphate also (Farooqui and Bachhawat, 1972). In the present report we have made a study of the kinetic properties of this unique arylsulphatase A purified from chicken brain using p-nitrocatechol sulphate and cerebroside-3-sulphate as substrates

Enzymic studies on sulphatide metabolism in different stages of experimental allergic encephalomyelitis

The activities of three enzymes-cerebroside sulphotransferase, 3'-phospho-adenosine 5'-phosphosulphate synthesizing enzyme and arylsulphatases A and B have been studied in various developmental and recovery stages of experimental allergic encephalomyelitis. The concentrations of cerebroside and sulphatide were also analysed during these stages. It was observed that the sulphatide concentration decreased during the development of the disease, with a concurrent increase in the activity of arylsulphatase and vice versa during the recovery stages. 3'-Phosphoadenosine 5'-phosphosulphate synthesis as well as sulphotransferase activity increased during the pre-acute stage of the disease, reached a maximum at the acute stage and decreased during recovery stages