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A Spector

Publications and source records attributed to A Spector.

At least 91 records · Page 5Linked to original sources
PubMed1978

Disulfide-linked high molecular weight protein associated with human cataract.

A major high molecular weight disulfide-linked protein has been isolated from cataractous lenses. It is only present in the water-insoluble protein fractions. This species has not been found in normal lenses of comparable age. Upon reduction of this fraction, polypeptides having molecular weights of approximately 60,000, 43,000, and 20,000 as well as a noncharacterized heterogeneous species are released. Similar sized polypeptides have been found in various noncovalently linked aggregates in both normal and cataractous lenses. Examination of the disulfide-linked protein fraction indicates that approximately 70% of the sulfhydryl groups are in the oxidized state. Although little change in the sizes of the other major polypeptides in the water-insoluble fraction is observed upon reduction, these components were also found to contain an appreciable disulfide content. Such results indicate that the only major lens fraction containing disulfide-linked polypeptide is the high molecular weight species and that the disulfides present in the remaining fractions are either intrachain disulfides or link polypeptides to small peptides.

Cataract↗
PubMed1978

Racemization in human lens: evidence of rapid insolubilization of specific polypeptides in cataract formation.

After early life, the dry weight of normal human lenses increases at a relatively constant rate with time. Transformation from soluble to insoluble material appears to occur at a comparable rate, resulting in a constant amount of soluble material. However, in cataract the insolubilization rate is accelerated. These observations are supported by determination of D-aspartic acid/L-aspartic acid ratios. The abundance of D-aspartic acid increases with aging at a constant rate in the insoluble fraction of normal lenses but does not change in the soluble fraction. However, in cataractous lenses there is a significant decrease in the ratio in the insoluble fraction. Examination of polypeptides isolated from reduced and alkylated soluble and insoluble cataractous lens proteins as well as other data suggest the following additional conclusions: (i) the 10,000-dalton polypeptide in the insoluble fraction is derived in part from degradation of an already insoluble precursor; and (ii) the lowered abundance of D-aspartic acid in the insoluble fraction of cataractous lenses is primarily due to the rapid insolubilization of the 43,000- and 20,000-dalton range components.

Age Factors↗
PubMed1977

Isolation and characterization of initiation fragments from lens 10S and 14S alpha-crystallin messenger ribonucleic acids.

The alpha-crystallin 10S and 14S messenger ribonucleic acids (mRNAs) for the B and A chains, respectively, were isolated from calf lenses. Initiation complexes were formed with both mRNAs after which the unprotected regions were digested with ribonuclease T1. A single fragment of approximately 45 nucleotides was obtained from both the 10S and 14S mRNAs. The fragments retained the ability to reform initiation complexes under standard conditions. Two-dimensional fractionation of ribonuclease T1 digests indicated considerable similarity between the 10S and 14S fragments. However, marked differences in the (U)G region were observed. The addition of the methylating agent S-adenosyl-L-methionine to the mRNA initiation system increases complex formation form two to five times, suggesting that methylation may be required for initiation.

Animals↗
PubMed1977

The bicistronic nature of lens alpha-crystallin 14S mRNA.

The A2 and B2 polypeptide chains of calf lens alpha-crystallin are synthesized on a 14S, 1500-nucleotide mRNA and a 10S, 735-nucleotide mRNA, respectively. The 10S mRNA is theoretically compatible with the size of the B2 chain, but the 14S mRNA contains approximately twice the required number of nucleotides necessary for A2 chain synthesis. This fact raises the question of the function of the additional nucleotide sequence in the 14S mRNA. The following observations on 14S mRNA suggest that it may contain an additional cistron. (i) Under a number of denaturing conditions, 14S mRNA continues to retain its initial size characteristics. (ii) In addition to synthesis of the A2 chain, 14S mRNA directs the synthesis of another polypeptide with the same electrophoretic mobility as that of the B2 chain. (iii) Molecular hybridization of the 14S mRNA with the cDNA produced from the 10S mRNA suggests that 2 mol of the cDNA bind to 1 mol of the 14S mRNA. (iv) Examination of the nucleotide sequences of the 10S and 14S mRNAs by two-dimensional maps of RNase A and T1 digests indicates marked similarity. The overall data suggest that the additional cistronic component may carry coding information for an alpha-crystallin polypeptide or a closely related polypeptide species.

Animals↗
PubMed1976

Human alpha-crystallin: characterization of the protein isolated from the periphery of cataractous lenses.

alpha-Crystallin has been isolated from the peripheral region of old cataractous lenses. It was found to be closely related to bovine alpha-crystallin and to human newly synthesized alpha-crystallin in terms of its amino acid composition, the size of its polypeptide chains and the lack of free NH2-terminal groups. However, in contrast to the simple urea gel electrophoretic polypeptide patterns obtained with the reference proteins, 11 polypeptides were detected in the preparation. Ten of the polypeptides were isolated and shown to be either A or B chains on the basis of their amino acid compositions and comparison of the peptide maps of their tryptic hydrolysates. The four B chains as well as the six A chains were closely related, with most of the tryptic peptides being common to all members of their respective group. A nomenclature based upon the urea gel electrophoretic mobilites of the polypeptides has been proposed to define each chain. It was found that this alpha-crystallin preparation is composed of at least two populations of macromolecules, one of which contains macromolecules greater than 5 X 10(6) daltons on the basis of gel filtration with Bio-Gel A-5m. The compositions of the two fractions were found to be essentially identical.

Aged↗
PubMed1976

Calf lens messenger ribonucleoprotein complexes. Characterization and comparison of template activity with corresponding mRNAs.

Lens messenger ribonucleoprotein complexes have been isolated from calf lens polysomes by sucrose gradient centrifugation after puromycin-induced dissociation. A 10 S mRNA was released from a 13 S messenger ribonucleoprotein complex and a 14 S mRNA from a 19 S messenger ribonucleoprotein complex. Two major protein components with molecular weights of approx. 64 000 and 40 000 were isolated from each of the messenger ribonucleoprotein complexes after RNAase digestion. Buoyant density determinations suggest that the messenger ribonucleoprotein complexes contain approximately one mol of each major protein species per mol mRNA. In contrast to lens mRNA, lens messenger ribonucleoproteins are poor templates for transcription with avian myeloblastosis virus reverse transcriptase. Similar results were also obtained with globin messenger ribonucleoprotein containing either two major protein species (or deficient in the lower molecular weight protein species). Polynucleotide phosphorylase eliminates the reverse transcription template activity of the lens mRNA. This effect is blocked in the messenger ribonucleoprotein. Such observations suggest that at least one of the protein components associated with lens messenger ribonucleoprotein may be located in the 3'-terminal region. Only a small variation in translation activity was observed between the messenger ribonucleoproteins and their respective mRNAs.

Animals↗
PubMed1976

Absence of low-molecular-weight alpha crystallin in nuclear region of old human lenses.

Examination of old human lenses indicates that low-molecular-weight alpha crystallin is not present in the inner 30-40%, the nucleus, of the lens. The remainder of such lenses, the periphery, contains normal levels of this protein. This finding is in marked contrast to observations in young lenses, where a large quantity of this protein is found throughout the tissue.

Aging↗
PubMed1976

Human alpha-crystallin. I. The isolation and characterization of newly synthesized alpha-crystallin.

Studies of the incorporation of 14C amino acids into human lens proteins demonstrate that an alpha-crystallin fraction takes up more than six times as much radioactivity as any other lens protein. Based on analyses with a calibrated Bio-Gel A-1.5 m column, a molecular weight of 4.9 x 10(5) +/- 5 per cent was obtained for this protein while sedimentation equilibrium analyses indicated a weight average molecular weight, Mw, of 7.5 x 10(5) +/- 4 per cent at 10,000 r.p.m. Gel electrophoresis in sodium dodecyl sulfate revealed two components with molecular weights of 22,000 and 20,000, values similar to those found with calf alpha-crystallin. Alkaline urea gel electrophoresis indicated one major polypeptide with a mobility similar to the B2 chain of calf alpha-crystallin and two major bands with mobilities between those of the calf alpha-crystallin A2 and A1 chains. Amino acid analyses of this newly synthesized alpha-crystallin gave a composition which with a few exceptions is very similar to that of calf alpha-crystallin. All three major polypeptides contained 14C amino acids. However, from the present data, it cannot be determined whether the three polypeptides were independently synthesized or a rapid transformation produced one of the labeled polypeptides in the A region. There appears to be between three and four times as many presumptive A as B polypeptides.

Amino Acids↗
PubMed1976

Human alpha-crystallin-III isolation and characterization of protein from normal infant lenses and old lens peripheries.

Alpha-crystallin isolated from the peripheries of old normal or cataractous lenses appears to be identical, consisting of eleven polypeptides, five B, and six A chains. In contrast, alpha-crystallin isolated from normal six-week-old human lenses has only three major polypeptides, corresponding to B1, A1, and A2 of the old human lens protein as well as small amounts of some of the other components. Comparisons with bovine alpha-crystallin are also reported. Based on gel filtration experiments with Bio-Gel A-1.5m, two distinct populations of alpha-crystallin were found in old lens periphery, one containing species greater than 1.5 X 10(6) daltons and another of approximately 9 X 10(5) daltons. In the cataract preparations, the higher molecular weight fraction is predominant. This fraction is not present in young lenses.

Aged↗