Myristoyl esters of lactose

Whereas lactose did not undergo a base-catalyzed transesterification with methyl esters of fatty acids, methyl beta-lactoside reacted under identical conditions to give mono- and di-myristates. This difference in behavior is explained in terms of the formation of an unreactive, internally chelated potassium-lactose complex. Supporting evidence for this hypothesis is the observed change in the anomeric equilibrium of lactose in the presence of potassium carbonate. The monomyristates of methyl beta-lactoside were assigned the structures of 3' and 6' derivatives, and it is concluded that the diesters are the 3',6', and 6,6' derivatives.     

Acidogenic fermentation of lactose

Cheese whey is the main component of waste streams from cheese manufacturing plants. Whey is a high biochemical oxygen demand (BOD) effluent that must be reduced before the streams are sent to the sewer. It is proposed in this article that the production of methane by anaerobic fermentation would be the best use of this stream, especially for small plants. Single-stage fermentation of lactose, the main component of whey, results in a very low pH and a stalled process. Two-phase fermentation will eliminate this problem. The acidogenic stage of fermentation has been studied at pH of between 4 and 6.5. The nature of the main products of the reaction have been found to be pH dependent. Below a pH of 4.5 a gas (CO(2) and H(2)) is produced along with ethanol, acetate, and butyrate. Above a pH of 4.5 no gas was produced, and the liquid products included less ethanol and butyrate and more acetate. A separate study on the conditions for gas formation showed that if the pH dropped for a short time below 4.5 gases were formed at all subsequent pH. This would indicate a change in population distribution due to the period at a low pH. By assuming that the desired products from the acidogenic stage were butyrate, acetate, and no gases, the optimum pH range was found to be between 6.0 and 6.5.     

Delayed lactose fermentation by enterobacteriaceae

Goodman, R. E. (University of California, Los Angeles), and M. J. Pickett. Delayed lactose fermentation by Enterobacteriaceae. J. Bacteriol. 92:318-327. 1966.-When 171 Citrobacter freundii strains and 14 Paracolobactrum arizonae strains examined, 51 of the C. freundii strains and 13 of the P. arizonae strains were found to be delayed or negative lactose fermenters. Of the slow fermenters, 65% yielded rapidly fermenting mutants in cultures undergoing delayed fermentation. Lactose fermentation could generally be hastened by increasing lactose concentrations. Many organisms which fermented lactose slowly grew readily on a medium containing lactose as the sole carbon source. Regardless of their ability to ferment lactose, all strains of C. freundii and P. arizonae investigated could be shown to possess beta-galactosidase. Delayed fermenters failed to take up lactose from the culture medium, whereas prompt fermenters did so readily. The beta-galactosidases of 12 strains of enteric bacteria were studied in crude cell extracts with respect to specific activity, stability, and activity at varying substrate (o-nitrophenyl-beta-d-galactopyranoside) concentrations, at varying pH, and in the presence of sodium, potassium, and magnesium. The widely varying specific activities and the approximate similarity of the Michaelis constants (about 2 x 10(-4)m) suggested that the strains investigated produced differing amounts of beta-galactosidase. Moreover, qualitative differences in the enzymes provided evidence that these strains synthesized different molecular forms of beta-galactosidase. The results suggested that organisms which ferment lactose only after a prolonged delay do so because they possess multiple defects in their lactose-metabolizing machinery.     

Stimulation ofEscherichia coli adenylate cyclase by lactose in strains carrying mutations in lactose permease

When a wild-type strain ofEscherichia coli contains lactose permease, the accumulation of cyclic AMP (cAMP) by intact cells isinhibited by lactose. This inhibitory effect of lactose is observed in a strain with a mutant cAMP phosphodiesterase and therefore involves a regulation of adenylate cyctase activity. Some E. coli strains carrying mutations in lactose permease show an effect opposite to that of the wild-type strain; the accumulation of cAMP by intact cells isstimulated by lactose, but only when the mutant permease is present. Insertion of lactose permease into the membrane of ceils can produce a change in the specific activity of adenylate cycIase; induction of the wild-type transporter is correlated with a decrease in the specific activity, while implantation of a mutant form of lactose permease can lead to an increase in the specific activity. From these data, it is suggested that the state of the lactose transporter in the cell membrane influences the activity of adenytate cyclase.     

Role of lactose on the production of d-arabitol by Kluyveromyces lactis grown on lactose

There are remarkably few reports on d-arabitol production from lactose. Previous studies in our laboratory have shown that the osmophilic yeast Kluyveromyces lactis NBRC 1903 convert lactose to extracellular d-arabitol. The present study was undertaken to determine the participation of osmotic stress caused by lactose on d-arabitol production by K. lactis NBRC 1903 and to provide the information on the kinetics of d-arabitol production from lactose by K. lactis NBRC 1903. It was confirmed that d-arabitol production was triggered when an initial lactose concentration was above 278 mmol L⁻¹. d-Arabitol yield increased with an increase in initial lactose concentration. The highest d-arabitol concentration of 79.5 mmol L⁻¹ was achieved in the cultivation of K. lactis NBRC 1903 in a medium containing 555 mmol L⁻¹ lactose and 40 g L⁻¹ yeast extract. Lactose was found to play two important roles in d-arabitol production by K. lactis NBRC 1903 grown on lactose. First, lactose was assimilated as the substrate both for cell growth and d-arabitol production. Second, a high lactose concentration induced cellular response to high osmotic stress and up-regulated the flow from d-glucose-6-phosphate to d-arabitol. The arrest of cell growth triggered d-arabitol production.     

乳糖吸收不良、乳糖不耐受与人体健康关系探讨

由于乳糖在人体生长发育和新陈代谢中发挥着重要作用,LM或LI不仅可诱发小儿佝偻病、成人骨质疏松,而且还可造成人体腹泻、影响婴幼儿脑组织和神经系统的构建,对婴幼儿的体格发育和智力发育造成损害。本研究对乳糖不耐受的病因及发病因素、分型、流行病学、临床及实验室诊断方法等做一概述,为临床实践和科学研究提供参考。     

Rearrangement of lactose on sterilization

Summary Thermal sterilisation of a lactose-based medium resulted in rearrangement of substantial amounts of lactose to lactulose which was not fermented.     

Continuous-flow monitoring of lactose concentration

A specific continuous-flow analytical system for determination of lactose concentration in a liquid mixture of constituent sugars was developed and tested based on a series of enzymatic reactions. Lactose and glucose oxidase immobilized on a phenol–formaldehyde resin were employed. More detailed study was carried out based on a reaction by-product quantitatively detected by an available iodide electrode. A multichannel proportioning pump fed two independently operated analytical streams eliminating thus the background glucose interference. With a goal of lactose concentration control in a fermentation process, the system response time delay was shortened to approximately 15 min. Apart from optimization of the analytical system operating parameters, the study indicates also the major application problem areas: lactase inhibition by galactose, galactose oxidation by glucose oxidase, and a partial loss of glucose oxidase activity in a prolonged continuous-flow operation. A manual Colorimetric Procedure was employed to verify the results of the potentiometric method.     

What's new with lactose permease

The lactose permease ofEscherichia coli is a paradigm for polytopic membrane transport proteins that transduce free energy stored in an electrochemical ion gradient into work in the form of a concentration gradient. Although the permease consists of 12 hydrophobic transmembrane domains in probable -helical conformation that traverse the membrane in zigzag fashion connected by hydrophilic loops, little information is available regarding the folded tertiary structure of the molecule. In a recent approach site-directed fluorescence labeling is being used to study proximity relationships in lactose permease. The experiments are based upon site-directed pyrene labeling of combinations of paired Cys replacements in a mutant devoid of Cys residues. Since pyrene exhibits excimer fluorescence if two molecules are within about 3.5Å, the proximity between paired labeled residues can be determined. The results demonstrate that putative helices VIII and IX are close to helix X. Taken together with other findings indicating that helix VII is close to helices X and XI, the data lead to a model that describes the packing of helices VII to XI.K. Jung, H. Jung and G. G. Privé are Postdoctoral Fellows of the Deutscher Akademischer Austauschdienst, the European Molecular Biology Organization, and the American Cancer Society (California Division), respectively.     

An enzymatic microassay for lactose

An enzymatic microassay for lactose using a lactase enzyme derived from Saccharomyces fragilis is described. The assay uses 50-μl samples, provides 100% hydrolysis of lactose, and is sensitive within the range of 12.5–500 nmol per sample. The assay has been validated against an assay for ¹⁴C lactose which involves thin-layer chromatographic isolation of lactose. The assay is sufficiently sensitive for use in physiologic studies.