3 research outputs found
Influence of Soil Humic and Fulvic Acid on the Activity and Stability of Lysozyme and Urease
Humic substances (HS), including
humic acids (HA) and fulvic acids
(FA), are important components of soil systems. HS form strong complexes
with oppositely charged proteins, which will lead to changes in the
enzyme activity. The effect of soil HS on the activity and stability
of two enzymes was investigated as a function of pH, ionic strength,
and mass ratio HS/enzyme. Humic acid (JGHA) and fulvic acid (JGFA)
are negatively charged, lysozyme is net positive at pH values below
10.4, and urease is net positive below pH 5.2 or net negative above
pH 5.2. The enzyme activities in the HS-enzyme complexes were suppressed
when the enzymes were oppositely charged to the HS. The largest activity
suppression was observed around the mass ratio HS/enzyme where the
HS-protein complex was at its isoelectric point (IEP). At the IEP
strong aggregation of the complexes led to encapsulation of the enzyme.
The ionic strength was important; an increase decreased complex formation,
but increased aggregation. Due to the larger hydrophobicity of JGHA
than JGFA, the reduction in enzyme activity was stronger for JGHA.
The enzyme stability also decreased maximally at mass ratio around
the IEP of the complex when HS and protein were oppositely charged.
When urease and HS were both negatively charged no complexes were
formed, but the presence of JGHA or JGFA improved the activity and
stability of the enzyme
Presentation_1_Frailty mediated the association between tooth loss and mortality in the oldest old individuals: a cohort study.pdf
IntroductionTooth loss is associated with increased mortality risk; however, the mechanism underlying this is still not clear. The objective of this study was to explore whether frailty mediates the association between tooth loss and mortality risk among the oldest old individuals.MethodsThe participants were followed up from 1998 to 2018 in the Chinese Longitudinal Healthy Longevity Survey (CLHLS). Frailty was constructed following a standard procedure. Mortality, frailty, and tooth loss were applied as the outcome, mediator, and independent variables, respectively. The Cox model was fitted, including possible confounders, for causal mediation analysis. A total effect (TE), an average causal mediation effect (ACME), an average direct effect (ADE), and a proportion mediated (PM) effect were calculated.ResultsDuring the 129,936 person-years at risk, 31,899 individuals with a mean age of 91.79  years were included. The TE and ADE of severe tooth loss on mortality were 0.12 (95% CI: 0.08, 0.15) and 0.09 (95% CI: 0.05, 0.13); the ACME of frailty was 0.03 (95% CI: 0.02, 0.03) with 21.56% of the TE being mediated.DiscussionThis study illustrated that tooth loss is associated with mortality, and frailty appeared to mediate the relationship. It is recommended that oral health indicators and frailty status be incorporated into routine geriatric assessments to promote optimal oral health and non-frailty status.</p
Lead Binding to Soil Fulvic and Humic Acids: NICA-Donnan Modeling and XAFS Spectroscopy
Binding
of lead (Pb) to soil fulvic acid (JGFA), soil humic acids
(JGHA, JLHA), and lignite-based humic acid (PAHA) was investigated
through binding isotherms and XAFS. Pb binding to humic substances
(HS) increased with increasing pH and decreasing ionic strength. The
NICA-Donnan model described Pb binding to the HS satisfactorily. The
comparison of the model parameters showed substantial differences
in median Pb affinity constants among JGFA, PAHA, and the soil HAs.
Milne’s “generic” parameters did not provide
an adequate prediction for the soil samples. The Pb binding prediction
with generic parameters for the soil HAs was improved significantly
by using the value <i>n</i><sub>Pb1</sub> = 0.92 instead
of the generic value <i>n</i><sub>Pb1</sub> = 0.60. The <i>n</i><sub>Pb1</sub>/<i>n</i><sub>H1</sub> ratios obtained
were relatively high, indicating monodentate Pb binding to the carboxylic-type
groups. The <i>n</i><sub>Pb2</sub>/<i>n</i><sub>H2</sub> ratios depended somewhat on the method of optimization,
but the values were distinctly lower than the <i>n</i><sub>Pb1</sub>/<i>n</i><sub>H1</sub> ratios, especially when
the optimization was based on Pb bound vs log [Pb<sup>2+</sup>]. These
low values indicate bidentate binding to the phenolic-type groups
at high Pb concentration. The NICA-Donnan model does not consider
bidentate binding of Pb to a carboxylic- and a phenolic-type group.
The EXAFS results at high Pb loading testified that Pb was bound in
bidentate complexes of one carboxylic and one phenolic group (salicylate-type)
or two phenolic groups (catechol-type) in ortho position