Properties of xanthine oxidase preparations dependent on the proportions of active and inactivated enzyme

McGartoll, Mary A.; Pick, Frances M.; Swann, John C.; Bray, Robert C.

doi:10.1016/0005-2744(70)90264-0

Cited by 38 publications

(20 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Feeding tungsten to lactating goats and cows also shows a strong decrease of milk XOR enzymatic activity in both cases without any influence on milk yield (Owen and Proudfoot 1968). Interestingly, milk contains by nature a mixture of active and inactive (de-molybdo) XOR (McGartoll et al 1970;Ventom et al 1988). While the enzymatic activity of milk XOR changes over time, the level of XOR protein remains relatively constant (Brown et al 1994(Brown et al , 1995.…”

Section: Discussionmentioning

confidence: 99%

The housekeeping gene xanthine oxidoreductase is necessary for milk fat droplet enveloping and secretion: gene sharing in the lactating mammary gland

Vorbach¹,

Scriven²,

Capecchi³

2002

Genes Dev.

200

173

View full text Add to dashboard Cite

Xanthine oxidoreductase (XOR) is the rate-limiting enzyme in purine catabolism occurring in most cell types. However, this housekeeping gene is expressed at very high levels in a number of mammalian tissues including the lactating mammary epithelium, suggesting additional roles for XOR in these tissues. Mice with targeted disruption of XOR were generated to assess these potential additional roles. XOR−/− mice are runted and do not live beyond 6 wk of age. Strikingly, however, XOR+/− females, although of healthy appearance and normal fertility, are unable to maintain lactation and their pups die of starvation 2 wk postpartum. Histological and whole-mount analyses showed that in XOR+/− females the mammary epithelium collapses, resulting in premature involution of the mammary gland. Electron microscopy showed that XOR is specifically required for enveloping milk fat droplets with the apical plasma membrane prior to secretion from the lactating mammary gland. We present evidence that XOR may have primarily a structural role, as a membrane-associated protein, in milk fat droplet secretion and thus XOR provides another example of "gene sharing". About 5% of women experience primary lactation insufficiency. The above observations suggest that human females suffering from xanthinuria, a deficiency in XOR, are potential candidates for lactation problems.

show abstract

Section: Discussionmentioning

confidence: 99%

The housekeeping gene xanthine oxidoreductase is necessary for milk fat droplet enveloping and secretion: gene sharing in the lactating mammary gland

Vorbach¹,

Scriven²,

Capecchi³

2002

Genes Dev.

200

173

View full text Add to dashboard Cite

show abstract

“…In the presence of excess substrate, three distinct EPR signals were detected for the Mo(V) center throughout the reaction: 'slow', 'rapid 1', and 'rapid 2', which is based on the time scales they were observed. 32,40,[51][52][53] The role of the sulfur atom in the Mo(V) center was investigated in detail by employing various methods such as its removal by cyanide or enrichment with 33 S. 54,55 Replacement of the essential Mo = S with Mo = O (desulfo-XO or desulfo-AO) results in a 'slow' signal. 47,56 The enzyme with this Mo = O form is catalytically nonfunctional.…”

Section: Epr Spectroscopymentioning

confidence: 99%

“…47,56 The enzyme with this Mo = O form is catalytically nonfunctional. 32,40,[51][52][53][54] Depending on the experimental conditions such as substrate identity or concentration the features of the 'rapid' signal vary. 57,58 Two inequivalent protons are coupled to the 'rapid type 1' signals in contrast to the 'rapid type 2' signals, which are coupled to two equivalent protons.…”

Section: Epr Spectroscopymentioning

confidence: 99%

Molybdenum-containing nitrite reductases: Spectroscopic characterization and redox mechanism

et al. 2016

View full text Add to dashboard Cite

show abstract

“…The proportion of functional sites was estimated from the activity/E4s0 (30TC, 340nm), taking the limiting value for fully active enzyme as 325 . The corresponding values for the milk enzyme were taken as e.,I = 72litre mmol1 cm-' (Bray, 1975) and limiting activity (23.50C, 295 nm)/E450 =197 (McGartoll et al, 1970).…”

Section: Estimation Of Concentration and Percentage Function Ality Omentioning

confidence: 99%

Studies by electron-paramagnetic-resonance spectroscopy and stopped-flow spectrophotometry on the mechanism of action of turkey liver xanthine dehydrogenase

Barber¹,

Bray²,

Lowe³

et al. 1976

Biochemical Journal

View full text Add to dashboard Cite

Studies by e.p.r. (electron-paramagnetic-resonance) spectroscopy and by stopped-flow spectrophotometry on turkey liver xanthine dehydrogenase revealed strong similarities to as well as important differences from the Veillonella alcalescens xanthine dehydrogenase and milk xanthine oxidase. The turkey enzyme is contaminated by up to three non-functional forms, giving molybdenum e.p.r. signals designated Resting I, Resting II and Slow. Slow and to a lesser extent Resting I signals are like those from the Veillonella enzyme, whereas Resting II is very like a resting signal described by K. V. Rajagopolan, P. Handler, G. Palmer & H. Beinert (1968) (J. Biol. Chem. 243, 3784-3796) for aldehyde oxidase. Another non-functional form that gives the Inhibited signal is produced on treatment of the enzyme with formaldehyde. Stopped-flow measurements at 450 nm show that, as for the milk enzyme, reduction by xanthine is rate-limiting in enzyme turnover. The active enzyme gives rise to Very Rapid and Rapid molybdenum(V) e.p.r. signals, as well as to an FADH signal. That these signals are almost indistinguishable from those of the milk enzyme, confirms the similarities between the active sites. There are two types of iron-sulphur centres that give signals like those in the milk enzyme, though with slightly different parameters. Quantitative reduction titration of the functional enzyme with xanthine revealed two important differences between the turkey and the milk enzymes. First, the turkey enzyme FADH/FADH2 system has a redox potential sufficiently low that xanthine is incapable of reducing the flavin completely. This finding presumably explains the very low oxidase activity. Secondly, whereas the Fe/S II chromophore in the milk enzyme has a relatively high redox potential, for the turkey enzyme the value of this potential is lower and similar to that of its Fe/S I chromophore.

show abstract

Properties of xanthine oxidase preparations dependent on the proportions of active and inactivated enzyme

Cited by 38 publications

References 13 publications

The housekeeping gene xanthine oxidoreductase is necessary for milk fat droplet enveloping and secretion: gene sharing in the lactating mammary gland

The housekeeping gene xanthine oxidoreductase is necessary for milk fat droplet enveloping and secretion: gene sharing in the lactating mammary gland

Molybdenum-containing nitrite reductases: Spectroscopic characterization and redox mechanism

Studies by electron-paramagnetic-resonance spectroscopy and stopped-flow spectrophotometry on the mechanism of action of turkey liver xanthine dehydrogenase

Contact Info

Product

Resources

About