PubMed Health⌕ Search

Biomedical subjects

J J Harding

Publications and source records attributed to J J Harding.

At least 127 records · Page 7Linked to original sources
PubMed1975

Changes in proteins of the human lens in development and aging.

A number of proteins have been isolated from the human lens at different stages of development, from before birth to old age. These proteins have been characterized and compared with each other and with corresponding proteins from bovine lens. Many similarities were found between human and bovine crystallins, but alpha-crystallin isolated from old human lenses using DEAE-cellulose, unlike bovine alpha-crystallin similarly isolated, is not found as large soluble aggregates. The amide contents of various lens protein fractions were determined. No extensive changes were found during adult life, but there was evidence that significant deamidation of alpha-crystallin had occurred before birth and possibly during infancy. The results are related to the unique development and aging of the lens.

Adolescent↗
PubMed1973

Altered heat-lability of a fraction of glutathione reductase in aging human lens.

An unusually heat-labile fraction of glutathione reductase appears in human lens at about an age of 32 years. No such change was found in glucose 6-phosphate dehydrogenase nor in 3-phosphoglycerate kinase. The change is an intrinsic property of glutathione reductase. A greater proportion of the altered glutathione reductase was found in the core, the older part, of the lens. No evidence of a second band of activity was obtained after electrophoresis. Possible interpretations of the results, including errors of protein synthesis, production of a new isoenzyme and post-synthetic changes, are discussed.

Adult↗
PubMed1972

Conformational changes in human lens proteins in cataract.

The reactivity of protein thiol groups in human lens and the susceptibility of the proteins to tryptic digestion were investigated. Both were found to be greater in some cataractous lenses, indicating that lens proteins have unfolded during cataractogenesis. Almost all the tyrosine in the proteins of the normal human lens reacts with tetranitromethane and is therefore probably on the outside of the major lens proteins.

Amino Acids↗
PubMed1970

Free and protein-bound glutathione in normal and cataractous human lenses.

Protein-bound glutathione was identified and measured in normal and cataractous human lenses. In a major group of cataracto us lenses the bound glutathione concentration was higher than normal. Study of normal lenses showed that their glutathione content is age-dependent, decreasing steadily from about 3.5mumol/g of lens at age 20 years to about 1.8mumol/g of lens at age 65 years. Cataract brings further decreases.

Adolescent↗
PubMed1968

The purification and amino acid composition of human uterus collagens, rheumatoid-arthritis-nodule collagen and ox tendon collagen.

Collagens and gelatins were isolated from human post-menopausal uterus, puerperal (post-partum) uterus, rheumatoid-arthritis-nodule and ox tendon. Different means of purifying collagen were studied and a method was devised that enables highly purified collagen to be obtained, even from the uterus. This method involves the use of a number of aqueous and organic extractants as well as digestion with elastase to eliminate elastin. The purity of the collagen preparations was assessed and they were used to study the amino acid composition of collagen. The amino acid compositions of all the collagens studied were similar to those of human bone and tendon collagen, but certain small differences were noted and are discussed. The soluble collagen extracted from some of the tissues was also studied.

Adult↗
PubMedDate not supplied

The untenability of the sunlight hypothesis of cataractogenesis.

The excess prevalence of cataract in third world countries led early this century to the hypothesis that sunlight causes cataract. The hypothesis, which ignored differences in diet, culture, poverty and prevalence of other diseases such as diarrhoea, received little support until about thirty years ago when biochemical studies were set up to explore the browning of lens proteins, which is a common feature of cataract on the Indian subcontinent. Initially these studies were encouraging in that exposure to sunlight caused some changes seen in cataractous lenses, but eventually the hypothesis was rejected because the first change in the laboratory was the destruction of tryptophan, but this was not found in brown cataract lenses. A brown nuclear cataract could not be produced artificially in the laboratory using sunlight or UV exposure. Exposure of laboratory animals has produced lens opacities, but in most experiments the doses required have also caused keratitis, conjunctivitis, iritis and inflammation. The cornea seems more sensitive than the lens, which is not surprising, as it gets the first chance to absorb damaging UV. The biochemical rejection of the hypothesis coincided with the re-start of the epidemiological studies. Most of these are simply latitude studies and are no more than a repeat of what was available sixty years ago. They do not help to find a cause. Two studies showed that cataract was less common at higher altitude in the Himalayas, but unfortunately led to opposing conclusions. On the basis of common knowledge that UV exposure was greater at higher altitude, the first altitude study led to the rejection of the sunlight hypothesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Cataract↗
PubMedDate not supplied

Postpartum psychiatric disorders: a review.

Postpartum emotional disorders generally fall into one of three categories: "blues," depressions, or psychoses. Such postpartum syndromes are described as to their presenting symptomatology, phenomenology, treatment, and prognosis. The role of the appropriate use of psychotropic medication in these conditions, after proper diagnosis, is also discussed. This overview is meant to be helpful to consultation-liaison psychiatrists and to other psychiatrists who work closely with obstetricians and primary care physicians.

Depressive Disorder↗
PubMedDate not supplied

Protection of enzymes by alpha-crystallin acting as a molecular chaperone.

How can enzymes function in the centre of a crowded lens over the many decades of an individual's life when the same proteins are usually turned over in a period of days or h in most other tissues? The discovery that alpha-crystallin could function as a molecular chaperone in-vitro has led to the hypothesis that alpha-crystallin could protect enzyme activities against various stresses. In the laboratory the authors have focused on the effect of alpha-crystallin on the activity of enzymes upon exposure to a chemical or thermal stress. The authors have demonstrated that enzymes are rapidly inactivated by sugars, sugar phosphates, steroids and cyanate. These compounds are elevated in diseases such as diabetes, diarrhoea and renal failure, all of which are risk factors for cataract. alpha-Crystallin has been shown to protect specifically against both chemically- and thermally-induced inactivation. Some enzymes are protected with a stoichiometry of one or two enzyme molecules protected per alpha-crystallin aggregate, consistent with a chaperone-like structure. However with other enzymes a more efficient protection occurs consistent with a micellar structure or binding on the outside of alpha-crystallin molecules. Investigation of complex formation indicates that although stable complex formation between enzymes and alpha-crystallin may be involved in protection of enzymes against thermal inactivation, protection against chemically-induced inactivation may be more dynamic in nature.

Aging↗
PubMedDate not supplied

The ageing lens.

The human lens grows by a process of epithelial cell division at its equator and the formation of generations of differentiated fibre cells. Despite the process of continuous remodelling necessary to achieve growth within a closed system, the lens can retain a high level of light transmission throughout the lifetime of the individual, with the ability to form sharp images on the retina. Continuous growth of the lens solves the problem imposed by terminal differentiation within a closed, avascular system, from which cells cannot be shed. The lens fibre tips arch over the equator to meet anteriorly and posteriorly and form branching sutures of increasing complexity. The stages of branching may create the optical zones of discontinuity seen on biomicroscopy. The lens is exposed to the cumulative effects of radiation, oxidation and postranslational modification. These later proteins and other lens molecules in such a way as to impair membrane functions and perturb protein (particularly crystallin) organisation, so that light transmission and image formation may be compromised. Damage is minimised by the presence of powerful scavenger and chaperone molecules. Progressive insolublisation of the crystallins of the lens nucleus in the first five decades of life, and the formation of higher molecular weight aggregates, may account for the decreased deformability of the lens nucleus which characterises presbyopia. Additional factors include: the progressive increase in lens mass with age, changes in the point of insertion of the lens zonules, and a shortening of the radius of curvature of the anterior surface of the lens. Also with age, there is a fall in light transmission by the lens, associated with increased light scatter, increased spectral absorption, particularly at the blue end of the spectrum, and increased lens fluorescence. A major factor responsible for the increased yellowing of the lens is the accumulation of a novel fluorogen, glutathione-3-hydroxy kynurenine glycoside, which makes a major contribution to the increasing fluorescence of the lens nucleus which occurs with age. Since this compound may also cross-link with the lens crystallins, it may contribute to the formation of high-molecular-weight aggregates and the increases in light scattering which occur with age. Focal changes of microscopic size are observed in apparently transparent, aged lenses and may be regarded as precursors of cortical cataract formation.

Aging↗