The phrase "activity has been speculated" is correct and usable in written English.
It can be used when discussing theories or assumptions regarding a particular activity or event that is not confirmed.
Example: "The activity has been speculated to have significant impacts on the local ecosystem, though further research is needed."
Alternatives: "activity has been conjectured" or "activity has been hypothesized".
Tubal abnormalities and dysfunction, such as altered contractility or abnormal ciliary activity, have been speculated to lead to tubal ectopic pregnancy.
It would be interesting to investigate whether JNK signalling is altered in loss-of-function mouse models where alterations in synaptic activity have been speculated to be a possible root cause of Batten's disease.
This suggested that the crude system contained deubiquitination activity, which has been speculated to influence the timing of degradation from the ER (Blount et al., 2012; Lederkremer and Glickman, 2005; Feldman and van der Goot, 2009).
Catalytic activity of oxidoreductase (redox reactions) has been speculated to be crucial for the survival of host plants, since it is required for energy transduction, operation of many anabolic and catabolic pathways, nutrient assimilation, and for defence against disease organisms [ 25].
Since LIPH encodes PA-PLA1α with a pla1 activity expressed in the skin, it has been speculated that loss-of-function of LIPH would reduce the production of LPA in hair follicles that could affect the migration, differentiation, or proliferation of keratinocytes, culminating in the arrest of hair growth [13].
It has been speculated that QPRT activity increases in response to neurodegenerative events [ 20].
It has been speculated that the antimicrobial activity associated with TasA may help provide protection to the cells within the biofilm (Romero et al. 2010).
It has been speculated that the increase of beta activity in schizophrenia is caused by chronic hyperarousal maintained by the brain stem reticulate activation system [ 16].
Increased TI in cancer has been speculated to originate from a defective proofreading activity of RNA polymerases.
In addition to phosphorylation, it has been speculated that acetyltransferases might also regulate the activity of RNA pol I transcription factors.
