278
GEORGE G. LATIES
gendered by a sudden spate of protein breakdown and resynthesis. The
implication of the foregoing interpretation is that the rate of protein
synthesis in the developing apple is controlled by the availability of
amino acids. This presumption is not readily reconciled with the observation that a considerable and constant pool of soluble nitrogen persists in
the presence of a constant quantity of protein for almost 100 days previous to the climacteric. More inconsistent still is the absence of net protein synthesis in response to a pronounced influx of soluble nitrogen into
the fruit just after the beginning of the climacteric. Protein synthesis is
not observed until some 20 days thereafter.
The correlation between the climacteric respiratory rise and the onset
of net protein synthesis in the apple fruit is much more pronounced in
Hulme's experiments than in those of Pearson and Robertson. In
Hulme's view the climacteric is engendered by the sudden recrudescence
of the synthetic process, which is in no way dependent upon concomitant proteolysis. The fact remains that the respiratory rise usually
somewhat precedes overt protein synthesis, and is always more precipitous than the increase in protein. Consequently, Hulme has suggested
that the protein increment during the climacteric is comprised of one or
more respiratory enzymes which cause an increase in respiration apart
from that brought about by the process of protein synthesis. In view
of the difficulties involved in rigorously attributing the climacteric to
the onset of protein synthesis, it may prove more tenable to assume that
some underlying factor controls both the climacteric and the synthesis
of protein. This underlying factor, whatever it might prove to be, must
in most instances be closely related to the production of ethylene, to its
function, or to both, since ethylene has consistently been implicated as
the metabolic product intimately associated with the development of
the climacteric (Biale, 1950; Biale et al, 1954; Kidd and West, 1945).
The activity of mitochondria from the flesh of apples of different stages
of maturity has been tested with respect to their ability to oxidize succinate, malate, and citrate (Pearson and Robertson, 1954). The Qo 2 (N)
was quite low for each of the substrates. A rise in total activity for each
substrate occurred concomitantly with the onset of the climacteric, the
activity being doubled. However, the control rate, in the absence of
added substrate, also increased sharply at the same time, and there was
no significant net increase in malic or citric oxidase activity, although the
increase in succinoxidase activity may be real. Since the particles were
apparently not resuspended and washed, the endogenous activity may
simply reflect the level of some contaminating substrate of unspecified
nature. If that were the case, and the contaminants should prove to be
organic acids, it might be unjustified to subtract the endogenous activity
GEORGE G. LATIES
gendered by a sudden spate of protein breakdown and resynthesis. The
implication of the foregoing interpretation is that the rate of protein
synthesis in the developing apple is controlled by the availability of
amino acids. This presumption is not readily reconciled with the observation that a considerable and constant pool of soluble nitrogen persists in
the presence of a constant quantity of protein for almost 100 days previous to the climacteric. More inconsistent still is the absence of net protein synthesis in response to a pronounced influx of soluble nitrogen into
the fruit just after the beginning of the climacteric. Protein synthesis is
not observed until some 20 days thereafter.
The correlation between the climacteric respiratory rise and the onset
of net protein synthesis in the apple fruit is much more pronounced in
Hulme's experiments than in those of Pearson and Robertson. In
Hulme's view the climacteric is engendered by the sudden recrudescence
of the synthetic process, which is in no way dependent upon concomitant proteolysis. The fact remains that the respiratory rise usually
somewhat precedes overt protein synthesis, and is always more precipitous than the increase in protein. Consequently, Hulme has suggested
that the protein increment during the climacteric is comprised of one or
more respiratory enzymes which cause an increase in respiration apart
from that brought about by the process of protein synthesis. In view
of the difficulties involved in rigorously attributing the climacteric to
the onset of protein synthesis, it may prove more tenable to assume that
some underlying factor controls both the climacteric and the synthesis
of protein. This underlying factor, whatever it might prove to be, must
in most instances be closely related to the production of ethylene, to its
function, or to both, since ethylene has consistently been implicated as
the metabolic product intimately associated with the development of
the climacteric (Biale, 1950; Biale et al, 1954; Kidd and West, 1945).
The activity of mitochondria from the flesh of apples of different stages
of maturity has been tested with respect to their ability to oxidize succinate, malate, and citrate (Pearson and Robertson, 1954). The Qo 2 (N)
was quite low for each of the substrates. A rise in total activity for each
substrate occurred concomitantly with the onset of the climacteric, the
activity being doubled. However, the control rate, in the absence of
added substrate, also increased sharply at the same time, and there was
no significant net increase in malic or citric oxidase activity, although the
increase in succinoxidase activity may be real. Since the particles were
apparently not resuspended and washed, the endogenous activity may
simply reflect the level of some contaminating substrate of unspecified
nature. If that were the case, and the contaminants should prove to be
organic acids, it might be unjustified to subtract the endogenous activity