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Year : 1979  |  Volume : 27  |  Issue : 2  |  Page : 32-34

The reactivity of sulf hydryl groups in the normal lenses of albino rat (Rattus norvegicus Berkenhaut) and guinea pig (Cavia porcellus Linnaeus)

Department of Zoology, University School of Sciences, Gujarat University, Ahmedabad, India

Correspondence Address:
U M Rawal
Department of Zoology, University School of Sciences, Gujarat University, Ahmedabad
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Source of Support: None, Conflict of Interest: None

PMID: 541028

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How to cite this article:
Rawal U M, Rao G N. The reactivity of sulf hydryl groups in the normal lenses of albino rat (Rattus norvegicus Berkenhaut) and guinea pig (Cavia porcellus Linnaeus). Indian J Ophthalmol 1979;27:32-4

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Rawal U M, Rao G N. The reactivity of sulf hydryl groups in the normal lenses of albino rat (Rattus norvegicus Berkenhaut) and guinea pig (Cavia porcellus Linnaeus). Indian J Ophthalmol [serial online] 1979 [cited 2021 Feb 25];27:32-4. Available from: https://www.ijo.in/text.asp?1979/27/2/32/31235

The enzymatic activities of SH enzymes depend mainly on free SH groups. Since last few decades attention was paid to the impor­tance of the SH groups in the formation of cataract. Sellows[2] and Dische et al[6] observed a considerable change in the SH content during the cataract process. According to Price et al[14] the change in the protein SH is observed in the later stage of irradiated cataract. Dische and Zil[5] suggested that the disappearance of the SH groups during the cataract process is due to the oxidation of the SH to-S-S-groups. They also suggested that the oxidation of SH groups occurs not only in the cataract process, but also in the transformation of soluble protein to insoluble protein of the lens. The earlier investigations[8],[4],[2] sub on experimental and senile cataracts have shown an increase in the content of water insoluble protein and a decrease in the content of total protein. Francis et al[8] also observed a decrease in the amount of soluble protein. Due to the disappearance of SH groups in the cataract formation and their importance in the maintenance or lens trans­parency, we have studied the reactivity of the lens thiols to the mild oxidizing conditions.

Such study may give an understanding of the reactivity of different types of lenticular SH groups during the cataract formation. In the present investigation, we have reported the reactivity of glutathione thiols (GSH) and protein thiols (PSH) to the mild oxidizing conditions in the lenses of laboratory animals­rat and guinea pig.

  Material and methods Top

The adult animals, maintained with standard feeds (Hindustan Lever Limited) were used for the experiments. The animals were anaesthetized and the eye balls were excised immediately. The complete lens was dissected out carefully without damaging the lenticular membrane. The lenses were washed with double distilled water and the excess of water was removed by blotting the lenses with filter paper. The wet weight of the lens was taken without delay. The method of Kinoshita and Merola[11], with slight modifications was used for the incubation of the homogenates. The lenses were homogenized in 0.18 M Tris buffer (pH 8.0) at 4°C. The amount of buffer used for homogenization was to give a final dilution of one lens in 1 ml. of buffer. The copper ions were used in the concentration of cupric ion 2 x 10-10 -5 M in the buffer. The homogenates were incubated under oxygen at 35+1°C. One set was made without cupric ions and another one with cupric ions. The aliquots were taken at various time intervals for the estimation of total thiols (TSH) and GSH.

The content of TSH was determined using Eliman's reagent[7] 3,3-dithiobis 6-nitrobenzoic acid as described by Asghar et. Al[1]. The amount of GSH was determined according to the method of Grunert and Philips[9]. The PSH was taken as the difference between the TSH and GSH. The values expressed are the mean of six determinations.

  Results Top

The contents of PSH and GSH in the lenses of rat and guinea pig are shown in [Figure - 1]. It was observed that the content of PSH is nearly six times higher that that of GSH in both the rat and guinea pig. It was also found that the levels of PSH and GSH vary from animal to animal. In the homogenates of rat lens incuba­ted with 100 per cent oxygen and without copper (H) ions, the change in the PSH was minimal. Homogenates flushed with oxygen and copper (11) ions shown a substantial change in the PSH content [Figure - 2]. About 35 per cent of the PSH disappeared in the samples collected after five hours incubation. A gradual decrease was observed in the GSH level in the homogenates having no copper (11) ions. However, the oxidation of GSH was rapid in presence of cupric ion. The complete oxidation was brought within one hour incubation.

The same pattern of results were observed in the guineapig lens homogenates [Figure - 2], But it was found that the rate of oxidation of PSH and GSH were more, as compared to the oxidation of PSH and GSH in the rat lens homogenates. After five hours incubation, the PSH level was found to be 42 per cent. The content of GSH was found almost negligible in the homogenates incubated with cupric ions and collected after one hour incubation.

  Discussion Top

The earlier studies[13],[11] on the normal bovine and human lenses and the present study on the normal rat and guinea pig lenses have drawn a relevent pattern of observations for the oxidation of SH groups to the mild oxidizing conditions. These studies were of importance to know how rapidly the different types of lenticular SH groups undergo oxidation. The reactivity of PSH to oxidation was found to be sluggish in the absence of cupric ion. However, the substantial reduction in the content of PSH in the presence of cupric ion suggested that in certain pathologic conditions, the PSH groups in the lens may readily undergo oxidation to form disulphide bonds. This may result in the intermolecular cross-linking which ultimately ends in the increasing of molecular weights of proteins. It is important that the extensive disulphide formation might result in insolubiliza­tion of protein as already stated by Dische and Zih, Pirie et all', Dische et al[14] and Harding.[10]

The disappearance of GSH even before one hour incubation in the presence of cupric ion makes relevant to its earlier diminution in the cataract process. The more resistancy of PSH to oxidation when compared to GSH may be the reason of its later diminution in the cataract formation. Harding 10 has already shown a four to seven fold increase in the amount of disulphide in cataracts. This type of disulphide formation during the progress of cataract may affect the activities of SH enzymes, which in turn affect the metabolic processes of the lens. However, the studies by Kinsey and Merriam[12] and Dailsley[4] on glutathione synthesis do not exclude the above hypothesis.

  Summary Top

A comparative study is made on the susceptibility of the thiol group in the albino rat and guinea pig lenses to oxidation by exposing the lens homogenates to an atmosphere of oxygen both in the presence and absence of traces of copper (11) ions. The susceptibility of protein thiols to oxidation was found con­siderably less compared to the susceptibility of glutathione thiols. The reactivity of different thiols was varied from animal to animal. The reactivity of these thiol groups to oxidation was discussed in relevance to their diminution in the cataract formation.

  Aknowledgements Top

Thanks are due to Professor V.C. Shah, Head of the Zoology, for providing the labora­tory facilities. The-financial help from Gujarat State to one of us (GNR) is greatly acknow­ledged.

  References Top

Asghar, K., Reddy, B.G. and Krishna, G., 1975, J. Histochem. cytochem,, 23, 774.  Back to cited text no. 1
Bellows, O.G., 1944, Cataracts and anomalies of the lens, (St. Louis, Mosby)  Back to cited text no. 2
Clark, R., Zigman, S. and Lerman, S., 1968, Exp. Eye. Res., 8, 172.  Back to cited text no. 3
Daisley, K.W., 1955, Biochem., J. 60, XI.  Back to cited text no. 4
Dische, Z. and Zil, H., 1951, Am. J. Ophtal., 34, 104.  Back to cited text no. 5
Dische, Z., Borenfreund, E. and Zelmenis, G., 1956, AMA. Arch. Ophthal., 55, 633  Back to cited text no. 6
Eliman, G.L., 1959, Arch. Biocphem. Biophys., 82, 70.  Back to cited text no. 7
Francois, J., Rabaey, M. and Stockmans, L., 1965, Exp. Eye. Res., 4, 312.  Back to cited text no. 8
Grunert, R. and Philips, P.H., 1951, Arch. Biochem., 30, 217.  Back to cited text no. 9
Harding, J.J., 1972, Exp. Eye. Res., 13, 33.  Back to cited text no. 10
Kinoshita, J.H. and Merola, L.D., 1973, The human lens in relation to cataract (North-Hol­land, N.Y.) 173.  Back to cited text no. 11
Kinesy, V.E. and Merriam, F.C., 1950, AMA. Arch. Ophthal., 44, 370.  Back to cited text no. 12
Merola, L.D. and Kinoshita, J.H,, 1957, Ain. J. Ophthal., 44, 326.  Back to cited text no. 13
Pirie, A., Van Heyningen, R. and Boag, J. W., 1953, Biochem. J., 54, 682.  Back to cited text no. 14


  [Figure - 1], [Figure - 2]


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