Aging of Spider Silks.

4 Pages·1994·0.27 MB·Danish

by  Shigeyoshi Osaki

Ada arachnol., 43 (1);
1-4, June 30, 1994
Aging of Spider Silks
Shigeyoshi OsAKII'
大嫡茂芳1):ク モの糸の老化現象
Abstract Effect of ultraviolet rays on drag lines, which were secreted at different
life stages of spider Nephila dar ata, was studied from the aging point of view . The
radicals due to the degradation of protein molecules were measured as a function of
the irradiation time of ultraviolet rays and the spider age by the electron spin reso-
nance ESR method. It was found that the radical intensity for drag lines from the
mature spiders was larger than that from the juvenile spiders. This finding suggests
that the aging should be considered for the silks secreted from the old spiders .
Introduction
It is one of the scientific problems to study the aging not only of the biological
tissue (YAMAMOTO et a!.,1988; OsAKI,1990) but also of the biomaterials secreted from
living animals.
Spider silks such as drag lines secreted from the spider body have been studied
from mechanical, physico-chemical, thermal, and optical points of view (e.g. WORK,
1976; WORK & MOROSOFF, 1992; GOSLINE, 1984; OSAKI, 1989 a, b). The drag lines
are very important for the spider to move, descend from trees, prey insects and
make orb-webs. The orb-web is irradiated outdoors by ultraviolet rays. It is
interesting to ask from the aging point of view how this irradiation affects spider
silks at different life stages. Nephila clavata spiders in Japan are born in May of
spring and die in November of autumn. We have reported that the seasonal
change in color of drag lines (OsAKI, 1989 b) and the change in their amino acid
composition (OsAKI, 1989 a) with age. However, the aging of the spider silk has
not as yet been studied.
The present study concerns the aging of spider silks based on the effect of
ultraviolet rays on the drag lines secreted at different stages of life.
Materials and Methods
The samples used were drag line silks forcibly pulled out of the bodies of many
spiders of Nephila clavata L. KOCH, 1878 collected from May (just after birth) to
October (just before death) 1991. The drag lines were automatically wound
around a rectangular frame at a rate of about 20 cm/sec. The body weight of
female N. clavata increased linearly from juvenile in spring to mature in autumn
l) Mycal Institute Inc., 2-2-9, Awajimachi, Chuo-ku, Osaka, 541 Japan
( ) -7' w , Q f T541 R ~ ix 2-2-9
Accepted April 13, 1994
2 S. OSAKI
(OSAKI, 1987). The electron spin resonance ESR spectra were measured by JES-
FEIX (JEOL, Japan), with irradiation of ultraviolet rays from the high
pressure
mercury lamp of 500 watts. The sample weight for ESR measurements was ca.
1.5 mg.
Results and Discussion
Figure 1 shows ESR spectra measured just after the ultraviolet rays were
irradiated for different minutes to the drag lines pulled from female N. clavata
collected on September 7. The magnetic field applied to the sample was 3,284
Fig. 1. Spectra of ESR for drag lines forcibly pulled from mature spider Nephila clavata
collected in September at different times of ultraviolet ray irradiation. The g value
was 2.007.
Aging of Spider Silks 3
gauss ±2,500 gauss and the g value was determined to be 2.007 for the observed
radical. It is well known that the ultraviolet rays induce the degradation of
polymer molecules due to the breaking of chemical bonds. Since the radical
intensity in the ESR spectrum expresses the degree of chemical decomposition of
silk protein, the increase in the intensity may be related to the aging of the drag
lines.
The relative radical intensity, which is defined as a ratio of the radical intensity
at a given time to the intensity at an initial time, for drag lines of N. clavata
collected at different seasons appears in Fig. 2 plotted against irradiation time of
ultraviolet rays. The radical intensity for drag lines secreted from the mature
spider initially increases with the time of irradiation and then approaches an
asymptotic value. On the other hand, the radical intensity I of drag lines secreted
from the juvenile spider increases very slowly with time and is much smaller than
that for the mature spider.
The empirical formula
I=1-+-C{1-exp (-Bt)} (1)
fits the data shown in Fig. 2, where C and B are constants associated with the
stage of spider's life. The values of C and B for the drag lines from the young
spider are much smaller than those from the old spider. Thus, the drag lines of
the mature spiders have many radicals in the protein molecules, which suggests that
Fig. 2. Time dependence of relative radical intensity under ultraviolet ray irradiation
measured by ESR for drag lines forcibly pulled from Nephila clavataa
4 S. OsAKI
the drag lines of the mature spiders in autumn are easier to degradate than the
juvenile spider in spring. This finding suggests that the aging should be considered
for the biomaterials such as the silks secreted from the old spider as living animals.
摘 要
ジョPウ グモの成長過程における異なる時期に分泌採取された牽引糸に対する紫外線の
影響を,老 化の観点から調べた.紫 外線照射によって生じるタンパク質分解ラジカルが,
ESR法 によって測定され,照 射時間および糸の採取時期の関数として調べられた.成 熟
したクモから採取した糸は,未 成熟のクモよりも分解しやすいことが判明した.こ の事実
から,老 化現象は加齢したクモから分泌した糸に対して考慮すべぎであることが示唆され
スL
References
GOSLINE, J. M., M. W. DENNY & M. E. DEMONT, 1984. Spider silk as rubber. Nature, 309: 551-
552.
OSAKI, S., 1987. The ecology and silks of spiders (I). Kagaku-to-seibutsu (Chemistry & Biology),
Tokyo, 25: 688-692. (In Japanese.)
1989 a. Thermal properties of spider's thread. Acta arachnol., 37: 69-75.
1989 b. Seasonal change in color of spider's silk. Ibid., 38: 21-28.
1990. Orientation test. Nature, 347: 132.
WORK, R. W., 1976. The force-elongation behavior of orb-web fibers and silks forcibly obtained
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& N. MoROSOFF, 1982. A physico-chemical study of the super contraction of spider major
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